Question:
I've tried to apply a sharp blade (the one that came witht he printer) to scrape the model off like I usually do but this model seems overly robust. What method can I do to take this off safely?

See image

Answer:
Unfortunately, you may have to destroy this part, or the build surface, just to get it off the plate. It looks really on there, and if you can't get under it even with a razor that further supports my gut instinct. It's happened to me before, just part of learning how to print with a particular material on a particular printer and build surface.
One thing to try before just hacking away at the part or replacing the build surface (which you may have to do anyway) would be to heat the plate back up to maybe 60-70*C, then hit the part with some freeze spray (or the poor man's version, turning a can of air duster upside-down). The rapid expansion-contraction may pop the part free. How effective this is depends on the plastic you used. PLA doesn't stretch and shrink much, but by the same token it's also very inflexible, so the stretching and shrinking it does do can stil pop the part off. This method's
really
effective for plastics like ABS that stretch/shrink a lot with heat. Remember to ventilate well; the principal component of these sprays is difluoroethane, which isn't great stuff to breathe in any significant concentration, and when spraying the liquid the resulting "steam" state of boiling liquid is much more flammable (so after the bed comes up to proper heat, I'd turn off the printer just in case).
EDIT: Per the comment to this answer, an alternate method would be to heat the plate even further, to about 80-90*C, which would heat the PLA beyond its glass transition temperature, softening it and reducing its adhesion. You would destroy the part, but parts can be reprinted, that's the beauty of owning a general-purpose computer-controlled additive plastic forming machine.
Your first layer including the brim looks a little close to the plate, which is part of the problem; you
really
squished that first layer down onto the bed. I would relevel the bed a bit further away, or (if you're happy with how actually level the bed is) set a Z-offset to increase first layer width. There's a very fine balance to be struck here; once you find it, printing (and removing said prints) becomes a lot easier.
In future, a build adhesive like Elmer's glue stick or hairspray (or a dedicated adhesive like 3DLAC or Bed Weld) also doubles as a release agent; the adhesive grabs the extruded plastic to keep it on the plate, but also prevents direct contact between two plastics and thus avoids any chemical bonding between the part and plate. Also consider upgrading to a flexible removable surface, like a magnetic BuildTak surface. Being able to take the bed off the printer and then flex the surface to help  pull a corner free (at which point you can slip a scraper in to lift the rest of it off) is a real boon to these types of situations.


Question:
Are there any statistics regarding how many units each manufacturer has sold, e.g. in 2019?

An article from 2016 claims Monoprice to have led the market back then - but all of the printers in that article have become obsolete since then.
Some manufacturers also claim theirs to be "one of the most popular" - but that likely doesn't translate to sales, at least for the more overpriced ones.

Answer:
Getting this data is not easy.  Many companies that make 3D printers are either private companies that do not report results or are larger companies where 3D printers are one of many products they manufacture.  Some companies study this information through mining public sources and surveying users for their opinions and experience.  The result of some of these studies are available for a fee.
Occasionally, a trade publication will survey data sources and produce an article.  In other cases, a trade pub will publish an article generously offered by a commercial contributor.
It is always difficult to know what is true when abstracting information from obscured, noisy, and biased information sources.
Your question itself includes a bias.  You use a words that include a value judgement: "but that likely doesn't translate to sales, at least for the more overpriced ones."
The article you reference is not a deeply researched investigative piece.  It is simply some product details for the five printers in 2016 which sold the most on Amazon.com.  It doesn't include printers which were not sold on Amazon, so it leaves out any printers which use a different distribution channel.  Also, the article include an link, probably which generate revenue back to the magazine, to each of the five printers sold through Amazon.
To summarize, it is very difficult to aggregate this kind of information.  Those who try to do so like to be compensated.  A list of the top five devices on Amazon is a biased list.


Question:
Say I wanted to print a plastic credit card like shape (like these), but with a QR code engraved. How could I do that for cheap? You can buy an "ID card printer" for $1,000-1,500 on Amazon, but that's way too much for printing one or two cards. Maybe down the road this would be a good option, but I kind of like the option of 3D printing the card from scratch, so the QR code bleeds halfway or all the way through the card, rather than just being printed on the surface. Is this possible for cheap? Maybe like this but not as fancy. Mainly (I'm new to all this) I am wondering what machine would accomplish this for low price yet good quality, and what other equipment I would need.

Basically, what printer is best for this type of task?

Answer:
FDM printer?
If you want to print one, maybe you should outsource it (let it print the tag on both sides), even the most affordable printers are in the \$100 - \$150 price range. If you want a printer and use it also to create ID tags, you could go for an FDM printer. Considering your request of having the tag inside (and through) the ID-card you need a dual filament option (one or two nozzle arrangement). If the tag can sit on top you can print it with a filament change with a single filament single nozzle printer. But, don't expect to get crystal clear prints (see experience printing signs below)!
Alternatives
As an alternative, you could print a blank PLA ID-card and laser mark the tag onto both sides, see e.g.
this video
.
If it is a small batch you can also consider printing/lasering stickers and stick these onto blank ID cards.
From experience
I've done some signs with black letters on a white background for "on-lay", inlay and through arrangements using a more expensive (for home use) dual extruder 3D printer (Ultimaker 3 Extended about \$5000,-) with PETG, but the results were not very satisfying. Usually the black smears out on or in the white no matter tweaking the options. Considering the size of an ID-card, the amount of tag squares, this is even more likely to happen when you print at that small size (the signs I printed were sized similar to the "A5" paper standard).
From my experience I would say that a 3D printer may not be the best solution for your task.


Question:
Which type of filament material(s) is safe to use as an in-wall box for regular, 120v wiring? For instance, an electrical outlet box.

In case it matters, location is the state of Washington, USA.

Answer:
I haven't tested the commercial "blue boxes" used to hold 120/240 V electrical outlets, switches, and splices to see how they behave when heated.  As such, this argument is based on intuition, which is intrinsically flawed as a logic device.  Never-the-less, I think the no extruded molten plastic (FFF) 3D printing filament will work.
The purpose of the junction box is to contain an overheating connection or switch and prevent it from causing a fire in the wall.  Any FFF filament will have a melting point below the ignition point of wood, and would therefore flow away from the overheating point.  It seems that any thermoplastic with a "normal" melting point would have this problem.
You might look at UV polymerized printing resins, such as are used in the Stratasys Objet, Form Labs, and Prusa SL1.  These printing processes aren't constrained to use plastics that can be melted or heat softened.  Because the polymerization can involve more aggressive crosslinking (polymerization) that FFF materials, they have the potential to be good for a higher temperature.
As an example of a high-temperature, non-melting plastic which could perhaps have an analogue in SLS resin, polyester "casting compound" is cross linked by a methyl-ethyl-ketone-peroxide catalyst to form clear solid.  24 hours after the polymerization starts, the solid does not melt under the influence of a hot air gun.  I tried to melt it and it would not melt.  It slightly softened, but the plastic cup I had cast it in was dripping away -- but the polyester was not melting.
I looked through the Stratasys materials and Form Labs materials and did not see a much higher temperature material.


Question: I got a new CR-10S 3D printer (I received it at Christmas). It has been printing just fine until yesterday, I was doing a print and it randomly paused, it did not restart on its own, I had to restart the print, then the item finished just fine.  I am printing today, a very small item, the printer now stopped 3 times.  How can I fix this, or do I need to return it?

Answer:
It would be great if you can write what the printer says when it stops.
I suggest you try printing other small objects. If that also stops then the printer itself has a problem. But if the printer prints other objects without stopping, then the one you want to print has bad gcode files. You also need to make sure to keep it up-to-date Cura. It would also be great if you can update your printer firmware. But other than that, problems could be heat problem, power problem, and other stuff; it would be great again if you can write the problem that says on the printer as it stops...


Question:
I could have sworn I read somewhere that when printing with TPU to make sure the part cooling fan is blowing. But I just did a quick Googling and couldn't find anything stating such on Matter Hackers or All3dp.

I currently don't have a part cooling fan attached (waiting for square nuts to come in). I've been able to get by printing PLA without the fan. I'm curious if this is going to be a major obstacle with TPU.

Answer:
You'll probably be fine printing TPU with no fan. I just started printing with TPU, and did a lot of test prints to find out what settings work. Fan made little difference. With hotend at 230 °C, which I started out with, 0-20% fan was fine. I eventually increased temperature to 250 °C, which made extrusion more consistent and allowed me to reduce linear advance K-factor somewhat, and at that temperature having a bit more fan (I'm using 40% now) seems to help the material hold its shape, but it mainly made a difference at higher print speeds (over 35 mm/s) where the motion of the nozzle was "pulling on" the still-very-soft material just extruded. At 30 mm/s and below, fan still doesn't seem very important.
All of this is likely to vary somewhat with the properties of your machine. However I think it's safe to say you should be able to find a combination of print speed and temperature that make it possible to get by with no fan.
Follow-up:
Upon further experimentation with TPU, I would say you really
don't want any fan at all
, except possibly for bridges. I've found significant distortion to shape just from air pressure from the fan, and at higher speeds the fan makes the print brittle just like what happens with PETG. Layers of TPU really seem to want time to melt together to bond, and without a fan blowing on them they don't seem to lose their shape during that time.


Question: Looking for something to smooth out a PLA print. Would Mod Podge be a good solution? Will it stick?

Answer:
From what I've read about Mod Podge, it is an adhesive with a vinyl acetate base. As such it is similar to both PVA (used for wash-away support) and ordinary white glue. One of the more common references to the product refers to it not being water proof, although the outdoor version of the product presents as being water-resistant.
As part of the research for this answer, I found references to overly-thick coats becoming milky. This follows a reference to applying thin multiple coats and allowing proper cure time between coats. That proper cure time is listed as 28 days.
Another set of posts suggest to cure the MP more rapidly than 28 days, one can heat the item in an oven to 175°F (80°C) which should not cause the PLA to melt, but may allow for sagging of unsupported parts. Testing is recommended.
MP is an adhesive, is known to stick to non-porous surfaces and would be no more harmful than glue stick for a PLA (or ABS) model.
Durability is uncertain. If you intend to paint the item after sealing/smoothing, you'll gain durability and water resistance.


Question: What is the thread pitch of the Ender 3's bed leveling screws? The diameter measures about 4mm. Are they M4 0.7 (coarse) pitch or 0.5 (fine) pitch? I'd like to develop rigorous formulas for the amount to turn the knobs by after measuring (or visually inspecting, since I can see an accurate 0.2 mm first layer decently well) leveling-test patterns in the corners rather than using a closed-loop tune-and-retry approach.

Answer:
I don't know what the value is, but there are a few ways to find out. It is very hard to measure this with a caliper, but it can be done, mark the upper and bottom of e.g. 10 windings and measure this with a caliper. Alternatively measure how much the screw drops after 10 full turns.
There are special tools that give you the answer directly, they cost a few Euros/bucks but can be very handy; a thread gauge, just place the 0.5 mm and the 0.7 mm beside the screw and you will instantly see which is the correct one.
I bought mine at a typical Chinese vendor site.


Question: I have an Ender 3 with a removeable build surface. The build surface backing has become warped - the center is at least 0.3 mm higher than the corners. I'm not sure what the material of this plate is - it's the part behind the BuildTak-clone surface that sits on the aluminum heat bed and is clipped to it. This makes it impossible to level the entire bed, and annoyingly tedious to level it enough just to use the center, since the paper method doesn't work at the corners. Can this be fixed, or do I need to source a replacement for it?

Answer:
I don't know what the value is, but there are a few ways to find out. It is very hard to measure this with a caliper, but it can be done, mark the upper and bottom of e.g. 10 windings and measure this with a caliper. Alternatively measure how much the screw drops after 10 full turns.
There are special tools that give you the answer directly, they cost a few Euros/bucks but can be very handy; a thread gauge, just place the 0.5 mm and the 0.7 mm beside the screw and you will instantly see which is the correct one.
I bought mine at a typical Chinese vendor site.


Question:
Marlin has a Linear Advance calibration pattern generator, but I find it's hard to use because:

It only prints the initial layer on the bed, where bed irregularities interfere with accurate reading of it.

It doesn't do proper retraction and priming, so a mess of strings and underextruded initial segments/non-adhesion mess up the results.

It's hard to visually evaluate.

Getting a very wide range of K values involves multiple runs.

It's hard to clean up.

Is there a better procedure for calibration of K value for linear advance?

Answer:
I don't know what the value is, but there are a few ways to find out. It is very hard to measure this with a caliper, but it can be done, mark the upper and bottom of e.g. 10 windings and measure this with a caliper. Alternatively measure how much the screw drops after 10 full turns.
There are special tools that give you the answer directly, they cost a few Euros/bucks but can be very handy; a thread gauge, just place the 0.5 mm and the 0.7 mm beside the screw and you will instantly see which is the correct one.
I bought mine at a typical Chinese vendor site.


Question:
I faced some problem with my 3D printer device. It seems the bed warms up without any problem, however, the hotend does not warm up!

Could you please help me identify what the problem is?

Answer:
I really hope the extruder doesn't warm up as this would be a problem with your stepper motor :)
I'm sure you mean the hotend doesn't heat up. This could be a number of things but i would start to double check the pinout in your code vs the pins on your mainboard and measure if it gives 12v/24v (depending on your PSU) output.
There's a lot more info required to properly help you.
What board are you using?
What OS are you using? Marlin or something else?
Share the relevant code of the OS for the hotend config/pinout
potentially share pictures of your wiring


Question:
Lately I noticed that there is a new type of nozzles (called airbrush nozzles?!?) available; typically found on those online overseas vendor sites. The nozzles are advertised for usage in E3D hardware, but are not found amongst the E3D genuine nozzles.

These nozzles look like this:

What are the basic physics principles or what is the engineering relevance for application of airbrush nozzles? (Gimmick or actual product improvement?)

Answer:
They are used for nonplaner 3d printing.
https://all3dp.com/4/nonplanar-3d-printing-gives-the-smoothest-top-layers/
The gist of it is, that You can achieve smoother, curvy top layers that are more true to form, buy using a nozzle like the one you mentioned. Also, they can be used to print multiple objects at the same time, where is faster to print 10 to 20 layers of one object then switch to the next object on the build plate, rather than having to print each layer of each object sequentially. This reduces build time, stringing, voids and the potential knocking off the part by the nozzle (as it moves to print the next object, since that object may have shrunk/expanded since the nozzle last visited it).


Question:
In analogy to: What glues for bonding printed PLA to injection-molded plastic?, what are the best glues to use for PETG?

I mostly print in PETG and have occasional failed prints which I usually reprint. But what if I'd like to repair a print e.g. a split between layers or a part broken off?

Knowing that PETG is more "greasy" than PLA, what typical glues can you use to create a good bond; this question excludes using heat to (re-)bond.

Answer:
From
forum
Bison plastic - works great for me, only it's not "quick dry" but it's very strong, not brittle, holds PETG and PLA very strongly.
  Buy paint stripper that is/contains methylene chloride (dichloromethane). It will solvent weld both PLA and PETG.
Or see
other forum
which recommends Eastman-910 (original brand of cyanoacrylate) or any equivalent, polyurethane glue, or even epoxy.


Question:
All of a sudden I seem to be having a lot of issues with under extruding on my Ender 3. The bottom layer (of height 0.1 mm) prints perfectly fine. This is done at 15 mm/s speed. However, The moment the print moves to layer 2 and above (at the default speed of 60 mm/s), I start hearing a lot of clicking noise on the extruder.

So far I have tried the following

Replace nozzle to eliminate clogs

Cleaned the inside of the hot end assembly

Calibrated extruder steps/mm

Reduced the layer height from 0.3 mm to 0.2 mm

Reduced feed rate to as low at 50 %

Cleaned the filament feeder assembly and verified that it is able to push the filament properly (Extruding when the print is not happening works just fine with no clicking)

Even with all the above, the issue is still persisting. I am not what else could be causing this.

I am printing with PLA at 200 C

Answer:
Not allowed to comment, so have to answer:
The temperature sensor is a thermally sensitive resistor. Unfortunately, the temperature is near the high limit of that sensor, and the manufacturing tolerances are very significant. That is why a temperature tower is important for each printer, as well as each filament. (I have 4 printers and each requires a different temperature for the same filament. My worst-case is out by 25 degrees! - it's the one I bought second-hand because the original purchaser couldn't get it to work. I could replace the NTC, but it is easier just to have settings to suit that printer.)
Filament does change over time. Lots of theories about why, but the practical response is to tune settings to suit the filament. The alternative is to modify the filament (eg drying, adding oil to surface, etc.), but even with really old filament, I've found adjusting settings (in the slicer, like Cura) to be the most generally workable solution.
Bottom line is to test, adjust settings and repeat until the system achieves the result you need. Treat most recommendations as serving suggestions, so use them as clues (but not rules) for the puzzles presented as 3D printing.


Question:
The e3D volcano features an extended heater block of length 20 mm with the cartridge heater running parallel to the filament.

The purpose of this is to increase the speeds at which filament can be printed (of course the extruder and other factors may still be limiting factors).

My question is how capable would this heat block be of printing at slow speeds with a 0.4 mm nozzle?

Is printing still possible at lower speeds or is the filament heated too much that jams occur? Is the retraction performance okay?

Answer:
Speaking from first hand experience running a Volcano hotend, mostly using a 0.6 mm nozzle, but I have used 0.4 mm as well. I can't really complain about any lower printing speed limit (low speeds are usually a solution to high speeds problems for me).
Just for completeness: I am using a DaVinci 1.1 Plus with custom firmware (modified Marlin) and an E3D Volcano hotend. No problems with the nozzle, clean prints! Note: I am using the Titan Aero as extruder but not using the included pancake motor! Went with the original motor of the DaVinci.
And as always: the parameters are key! Given a bit of tuning you can get amazing results! For PLA and ABS I can work without stringing. Although ABS seems to be prone to pitting (slight underextrusion at start of path). TPU and other flex are sometimes a bit of a challenge, but that's mainly due to my own lack of experience there.
The one important caveat here would be to also reduce the nozzle temperature. A possible theory here might be that the filament has more time and surface to heat up.
(Sometimes I go as much as 15 °C lower as compared to normal/high speeds! Usually lower speeds means small pieces for me and in term means a limit to the layer cooling time.)


Question:
I'm new to 3D printing and have bought a resin printer.

Cleaning with Isopropol Alcohol seems to be the rage, however I think this is unaware of cost savings.  It appears methylated spirits is ok and is 25% the cost of Isopropol Alcohol.

I'm now down to wondering if I should buy methylated spirits or turpentine (I ruled out kerosene as too flammable)?
I'm leaning towards methylated spirits, however would like input.

Factors I'm curious about:

Cost: same for methylated spirits and turpentine.

Evaporation/solvency: ?

Flammability: ?

Poisonous levels: ?

Resin object cleaning effect: ?

Skin effects: ?

Smell: ?

I checked a few sources.

Answer: I would personally stick to isopropanol. Be aware that 3D printing is a very expensive hobby, but health wise this is a better option. Methylated spirits can quickly become dangerous, and often can burn with a close to invisible flame, meaning that you may not even see if it is burning. Also, the fumes can quickly become dangerous, whereas after years of dealing with isopropanol I have noticed no ill effects. Cost should not be your primary concern, health of you and your printer should be.


Question:
I'd like to prefix this question with the fact that I know virtually nothing about 3D printers, aside from the general principles of how they work.

I've recently seen that SLS printers have become more affordable, to the point where in a few years they might be a compelling investment. I'm mainly interested in 3D printing miniatures for painting, and as such this one:

For scale, the miniature is about 150 mm long. I'm mainly worried about smaller details, such as the faces of the Gunner or Driver. Will a consumer-grade SLS printer be able to print to such level of detail?

Answer:
It's difficult to tell from your photo the level of detail required. A scale reference in the form of a metric ruler would be valuable. If, for example, the metallic eye on the gunner is 2 mm diameter, that would be 40 layers of 50 micron grains, allowing for substantial detail.
Consumer level SLS printers, such as the Sinterit Kit, use fifty micron nylon powder and is subject to some shrinking. This implies one can expect slightly smaller than fifty micron detail to appear.
One of our makerspace members purchased an SLS model from Shapeways. The surface is layer-free and one can see the individual granules under magnification. If you required a level of certainty of this detail, consider that you can create a model containing various levels of detail, then commission Shapeways to create it.
It's certain that they use a production level system, but one can inquire of Shapeways of the size of the powder that is used.


Question:
For practicality sake, I need to print a design such that there will be weight hanging parellel to the layer lines. Is there an infill pattern that would be better than others at handling this?

I realize that all kinds of infill will still have the same layer boundaries. Just wondering if choosing any given infill might provide better results.

Answer:
Yes, some infill patterns are better than others for preventing separation of layers. Basically (modulo some assumptions about uniformity of distribution of force), the shearing strength of the part in the Z direction at a particular layer is going to be proportional to the
surface area
of bonding between successive layers. So infill patterns that stack identical infill extrusions on top of each other at each layer should be expected to be much stronger than patterns where successive layers make only partial contact. In other words, "2D infill patterns" - grid, lines, triangles, tri-hexagon - should be a lot stronger than "3D infill patterns" - cubic, octet, gyroid, ... This matches my experience printing bolts oriented along the Z-axis - ones printed with gyroid snap easily unless other measures are taken to strengthen them, while ones printed with triangles are fairly strong (though nowhere near as strong as ones printed oriented in the XY plane.
If you have other reason to prefer a "3D infill pattern", its weakness can be mitigated mostly by increasing the infill line width, so that the lines of successive layers which don't entirely overlap still touch on more surface area. (Just increasing the infill line width also works to make "2D infill patterns" even stronger.) However, be aware that with high print speed typically used for infill, increasing infill line width can easily exceed the capability of your hotend, resulting in underextrusion, extruder skipping, and stringing all over the place.


Question:
Is it possible to convert an image image to STL file format?

E.g. I don't need the coloring, I need the lines.

Answer:
PNGs are 2-dimensional picture data files. STL however is a 3-dimensinal surface data files. The two are not inherently transformable into one another, as there simply is no 3rd dimension encoded in the PNG.
However, there are ways to generate a 3rd dimension from a color picture:
Lithophanes
take color information and use that as a degree of deviation from a base plane.
Using 3D design software that supports importing image data, one can trace the areas in 2D and
extrude
them to different heights or
emboss
the patterns into a block, even with different depths for each color.


Question:
I am Attempting to print this, from Blender

But Cura decides to fill in the middle part of the model.

I exported and imported the model from an STL file.

If anyone can answer this, that would be greatly appreciated.

Answer:
I would recommend using an actual CAD/CAM program, such as Autodesk Fusion 360, instead of using a 3d model program. Not only will this be able to directly export you finished model to Cura, and the models are made in a way that works with a 3d printing slicer, there will be more help around 3D printing for it.
Although it is slightly difficult to use to start with, as you become more proficient, it is a very powerful tool to have. . Fusion 360 is free for hobbyists or students. See this link for help activating:
https://www.autodesk.com/campaigns/fusion-360-for-hobbyists
.
Another option would be SolidWorks, although you do have to pay for this option, but it is much simpler to work with in my opinion.


Question:
My problem is that I have used a 3D printing machine from the University and found out that the cover for the car was not smooth even after using sanding paper and painting it.

What material would work best to print  the cover of the Cyber truck. I want it to be light and smooth.

I have to print it from any online companies that have this service here in Germany.

Answer:
I have 3D printed models which were then sanded using progressively finer grades of sandpaper, terminating with wet sanding using micromesh to 12000 grit. The result was smooth and shining without any coating applied.
If your original results were not acceptable, the process may have been flawed and should be re-considered for technique.
For your purposes, as a body for a radio controlled vehicle, you'll want to consider something that can manage an impact reasonably well. ABS is going to be less expensive and provide some energy absorption but will have layer lines that require sanding and finishing. Layer thickness plays a substantial part in providing for good results and a smooth finish. I used 0.100 mm layers to get optimum smoothness.
You could request your model to be created in nylon using the SLS method, but the surface will be granular and would also require sanding to accomplish a smooth finish.
SLA or MSLA resin printed models will provide a very smooth surface, but the material is brittle and may crack during "on-road" use. You may find a printing service which offers to create using a more flexible resin, but you'd have to request that or confirm the selection when placing the order.


Question:
I am thinking to use closed-loop stepper motors to prevent step loss and make the machine more accurate. What options (preferably low cost) are there for:

stepper motor + driver + encoder + microcontoller

Is building it from scratch worth it? E.g. Arduino Mega 2560 + RAMPS 1.4/1.5/1.6 + stepper motors (e.g. NEMA17) + drivers (e.g. A4988, DRV8825) + encoders (e.g. AS5047P, AS5047D, AS5048A, TLE5012B) + microcontrollers (e.g. STM32).

Answer:
A number of options exist, but keep in mind that cost will be a limiting factor.
(Small sidenote: cost depends on persective, financial cost does not equal mental cost. The tradeoff between buy or make depends also on your willingness to persist when things don't work right away.)
Before you start:
make sure that your printer has enough space to accomodate bigger motors.
So, what options are there?
Change your current configuration. If you are losing steps, it could very well be that it can be fixed in firmware.
Pro: No budget and nothing to lose.
Con: No shiny closed loop system. (Is that bad though?) Possibly need to configure and compile your own firmware.
MacGyver / DIY solution based on low lever components
Pro: Probably as cheap as you'll get depending on how you choose your components. Might be an interesting learning experience, not to mention the satisfaction afterwards. This could be the smallest build size you'll see in all the options.
Con: You'll need a decent amount of engineering and debugging. Might be tricky to mount the encoders.
Same as 1, but now consider using of the shelf stepper motors
with integrated encoders
.
Pro: Most robust option on a budget in my opinion due to the single mechanical piece (motor + encoder).
Con: Integrated encoders have a considerable cost and are large compared to their vanila versions.
Go for
off the shelf motor+encoder and drivers
.
Pro: No need to worry about driver configurations too much. Just plug in the numbers or set the dip switches. Very conveinient solution. Pretty much plug and play.
Con: This will already be challenging on a budget. Making a wrong mix and match might lead to unpredictable results such as drives going in overcurrent. (Which, believe me, is very frustrating for your application!)
If we are allowed to consider servo motors:
ClearPath-SD series
(Or any alternative for that matter!)
I'm just including this for completeness.
Pro: Performance wise a clear winner on pretty much any relevant level.
Con: You'll need a big budget!
Bottomline
: You'll probably want to give the first option a go before spending money. Next stop, you might want to take the second option (you already did research on different specific low level components), and if you have time to spare I'd go with that as well. If you are also on a budget timewise, I'd definively suggest to take the third option with existing driver boards.
The other options are more cost heavy and become real options in produciton environments, where downtime is also costsing money.
As to the microcontroller, take whatever you have available. Just know that more computational power will allow you to output steps faster and will allow for smoother movements. Lot's to talk about there as well!


Question: If I set my prints on the window sill (indoors) will the sunlight still be able to cure the resin? The problem with setting them outside is the wind knocking them over.

Answer:
The glass will block most of the uv light; but not all. It will depend on the type of light that the resin is sensitive to; in order to determine if it will continue to cure behind a glass window in direct sunlight. Some resins also sensitive to blue light. You will need to look at the material data sheet for the resin to be able to know for sure. Be advised though, that the resin does not stop curing, and will continue to cure slowly over time, just sitting on the desk.
https://www.thoughtco.com/does-glass-block-uv-light-608316
From the link:
Glass that is transparent to visible light absorbs nearly all UVB. This is the wavelength range that can cause a sunburn, so it's true you can't get a sunburn through glass. However, UVA is much closer to the visible spectrum than UVB. About 75% of UVA passes through ordinary glass. UVA leads to skin damage and genetic mutations that can lead to cancer. Glass does not protect you from skin damage from the sun. It affects indoor plants too. Have you ever taken an indoor plant outside and burned its leaves? This happens because the plant was unaccustomed to the higher levels of UVA found outside, compared with inside a sunny window.


Question:
I began build LCD printer and I want make some modifications.

What if I will place LCD below VAT? Will the display break when printing? what are the risks?
I seen a lot of printers and all of them use PP material for VAT bottom and attach with a lot of screws. I want make more simple VAT-LCD constructions and I think this construction transmis UV light better

Answer:
Short answer
Usually
no.
Long answer
There are several big factors that limit how small things you can print. The bigger ones are pretty much:
Positional accuracy and settings (limited by steps/mm in X, Y, Z)
Nozzle diameter
Now, why don't you need to care about steps/mm on the extruder that muchin the grand scale compared to the positional accuracy? Well, we have 1.8° per step, from which, with the diameter of the gear, 11mm, we get 0,1778 mm of filament extrusion or 0.428 mm³ of extruded plastic per full 1.8° step - which clearly is unsuitable to printing at all. But with the 16 micro-steps the shorter movements are possible and a single micro-step extrusion is in the area you calculated - I got to 0,0267 mm³, possibly the result of different rounding between us. With an assumed effective gear diameter of 11mm (usually the effective gear diameter is a little smaller, thus the 93 steps) we come to about 89.9 steps per mm of filament, which corresponds to about 2.4 mm³ of extruded plastic, or about 30 mm of line (with your given parameters), bringing us to about 3 microsteps per millimeter of line on the tray. So far, your math checks out. But that usually shouldn't be too much a limiting factor. We know from your given settings, that the
Configuration.h
will look like this, putting the microsteps into the steps/mm:
```
```
/**
* Default Axis Steps Per Unit (steps/mm)
* Override with M92
*                                      X, Y, Z, E0 [, E1[, E2[, E3[, E4]]]]
*/
#define DEFAULT_AXIS_STEPS_PER_UNIT   { 80, 80, 400, 93 }
```
```
As you don't have a micro-stepping driver, this part in
Configuration_adv.h
is non-functional:
```
```
// Microstep setting (Only functional when stepper driver microstep pins are connected to MCU.
#define MICROSTEP_MODES {16,16,16,16,16} // [1,2,4,8,16]
```
```
With the proposed 0.4 mm/0.2 mm line, we are still somewhat on the good side, allowing us about 1/3rd of a millimeter as the shortest line printable as a single step extrusion. That's a consistent with printing a simple, circular dot being printable with these settings - 0.4 > 1/3.
But once you get to smaller nozzle diameters, the limitation gets more noticeable: at a 0.2 mm nozzle and 0.22 mm line at 0.1 mm height, that's a 0.022 mm² crosssection, so the 1-step extrusion is equivalent to a full millimeter of line! That's much more bothersome in theory.
However, I haven't been able to witness the inability of showing that limit of lacking extrusion yet on my TronXY-X1 with a 0.2 mm nozzle - the steps/mm in it are also about 90-100 last I set them. The TronXY uses a very similar (virtually identical) extruder setup as the Ender 3, and it achieved printed lines of about 0.3 mm length at 0.1 mm layer height somewhat reliable, but the retraction made huge issues, which might also mask the problem.
I believe that it needs these smaller nozzles to amplify the problems to make them noticeable. It also should become more noticeable if you'd use 2.85 mm or 3 mm filament.
Ways to improve resolution
However, if printing with smaller nozzles, it might be a good idea to think about how one could improve the accuracy of the extruder system.
The most-easy way would be to alter the extruder and swap the gear to one of a
smaller
effective diameter - That way a single step accounts to
less
extrusion, which means, in turn, a higher number of steps/mm, and thus allowing for shorter extrusions that can be still achieved.
Next one might think about getting a different motor/driver setup that might have either more microsteps or generally a smaller step size.
Quadrupling the effective (micros)steps/mm would allow us to print about a 0.25 mm line on the 0.22 mm nozzle I proposed, being pretty much a spot - if it wouldn't be partially masked in other issues as I experience.


Question:
A question to those who have a 3D printer. Have you ever needed a spare throat or a heater block? Do they ever break?

I just bought some spare parts: heaters, thermistors, nozzles... However, I am not sure if buying throats and heater blocks make any sense.

Answer:
Short answer
Yes
Long answer
Heater bocks
A heater block is destroyed if one of the following happens
Threads stripped
Bent or otherwise deformed
stripped grub screw
All of these can happen by handling the block with too much force when securing nozzles, thermosensors or heater cartridges.
Throats
Throats can be destroyed, especially e3D v6 throats with their neck down on the center can be simply turned and broken in two. Lined throats can be heated too much and the liner destroyed, which not always can be replaced, mandating a spare part. And you can strip the threads.
Another chance to damage the throat is by using very hard material nozzles - stainless steel comes to mind. Such a nozzle would not deform itself like brass when tightened against the throat and might lead to damage to the end of the throat if exchanged several times.
Conclusion
If you run several printers or change nozzles regularly for whatever reason, it is a very good idea to have at least a complete set of spare parts on hand to fix problems that might occur during work on the printer. I have a fully assembled spare hotend waiting for its day to shine in case my current one breaks...


Question:
In my custom printer I have probe and nozzle at same height and configured Marlin this way:

#define NOZZLE_TO_PROBE_OFFSET { 43, -20, 0 }

On the bed I've a 2 mm glass. How I need to change the configuration? Do I need to act adding a positive Z offset? like this?

#define NOZZLE_TO_PROBE_OFFSET { 43, -20, 2 }

Answer:
No.
You define the Z-Value of the Nozzle to Probe offset mainly to get avoidance of collisions, but it is checked nowhere in the firmware code at all. Usually, the probe is mounted a millimeter or so above the nozzle anyway: you mount it in such a fashion that it triggers when the nozzle has the correct distance to the bed.
If you alter the bed by altering the distance between the nozzle and the metal part of the bed, you might need to alter the physical position of the probe to get the printer to trigger at the correct height, but you don't necessarily need to add a Z-offset.
You might, however, want to include it in the slicer for the case you want to print items in a sequence, which forces most slicers to try to do an error-avoidance pattern.


Question:
I'm using a 200x200 mm PCB Mk2B which connects to the MOSFET of the D8 pin on a RAMPS 1.4 shield. I used 12 V power source for heat bed so I connected positive to pin 1 and negative to both pin 2 & 3 of the bed. Heat bed worked properly. But the wires that connects power source to power supply pin on RAMPS were being heated badly. I think the problem is come from heat bed because when I unplugged heat bed, wires were cool down instantly.

Can someone helps me with this problem. I'm just a newbie in this area.

Answer:
I have an
open bug report/feature request
for this. Apparently Cura doesn't do it because some of Ultimaker's printers have underpowered power supplies that will shut off if you try to do both at the same time. I've been carrying a patch (note this is against CuraEngine not the Cura GUI) that fixes this:
```
```
diff --git a/src/FffGcodeWriter.cpp b/src/FffGcodeWriter.cpp
index de3c771c..ced22017 100644
--- a/src/FffGcodeWriter.cpp
+++ b/src/FffGcodeWriter.cpp
@@ -500,7 +500,7 @@ void FffGcodeWriter::processInitialLayerTemperature(const SliceDataStorage& stor
                 const Temperature bed_temp = scene.current_mesh_group->settings.get<Temperature>("material_bed_temperature_layer_0");
                 if (bed_temp != 0)
                 {
-                    gcode.writeBedTemperatureCommand(bed_temp, scene.current_mesh_group->settings.get<bool>("material_bed_temp_wait"));
+                    gcode.writeBedTemperatureCommand(bed_temp, false);
                 }
             }
         }
@@ -547,6 +547,18 @@ void FffGcodeWriter::processInitialLayerTemperature(const SliceDataStorage& stor
                 }
             }
         }
+
+        if (scene.current_mesh_group->settings.get<bool>("material_bed_temp_prepend"))
+        {
+            if (scene.current_mesh_group->settings.get<bool>("machine_heated_bed"))
+            {
+                const Temperature bed_temp = scene.current_mesh_group->settings.get<Temperature>("material_bed_temperature_layer_0");
+                if (bed_temp != 0)
+                {
+                    gcode.writeBedTemperatureCommand(bed_temp, scene.current_mesh_group->settings.get<bool>("material_bed_temp_wait"));
+                }
+            }
+        }
     }
 }
```
```


Question: Have people been using 3D printing to genuinely create a number of needed objects in their homes, and if so, what? Or is 3D printing better for special niche interests like art projects, home engineering projects, etc?

Answer:
Both.
3D printing is especially useful for creating replacement parts for things for which it would otherwise be difficult, expensive, or impossible to obtain a conventionally manufactured one. You may have seen in the news recently the
story about 3D printing being used to replace hospital ventilator valves
that were not available in time to save patients who needed them, and that normally cost \$11000 from the manufacturer. But the same kind of thing applies to regular household items too. For example, I've replaced broken wheels on my child's toy cars, a broken windshield washer fluid coupling in my car, and various similar things. I'm also planning to replace broken plastic wheel bearings in my vacuum cleaner (the manufacturer's design was atrociously bad and I'll probably adapt it to use real bearings with a 3D printed adapter), a window switch in my car, and lots of other things I can't remember at the moment.
Of course you can do craft and hobby things too. I don't think this really calls for examples/evidence.


Question:
I want to make an order with this configuration

Arduino MEGA 2650 R3

Ramps 1.6 Plus

2 TMC2130

2 Stepper motors 17hs3401

1 Fan

But I am not sure what voltage and current would be enough to make it work. The Ramps 1.6+ board has an input of 12V as you can see in the picture, but I have read that other people had to increase the voltage with a DC-DC converter.

So, would be 12V and 15A enough to make work that configuration?

Answer:
The easiest way to know how powerful the PSU should be is to download from
https://github.com/rcarlyle/StepperSim
the Excel workbook which simulates the power absorbed by the stepper motor. Input the motor specifications, check in the graph the max speed at which you plan to run it, check the absorbed power, add 20% for the various losses. Once you know the absorbed power, you can multiply by the number of stepper motors and obtain the current required, add 20% not to stress the PSU too much.
In you case, this is the result
Your motor will never absorb more than 7 W, 14 W for the two motors, around 20 W considering losses in the motors and overcapacity of the PSU. This means that around 2 A PSU will be perfect for your setup.
Previous answer, which may not be completely correct but still provides a useful background knowledge:
The TMC drivers limit the current to the value you set, which is most of the time lower than the datasheet. In no case you will need more than 1.3 A * sqrt(2) * 2 motors = 3.6 A. In fact, you won't need this much either.
When there is no field in a coil, the driver applies full voltage, but the current is low (initially zero) so you don't hit the 1.3 A per coil.
The current increases (the higher the maximum voltage available to the driver, the faster it increases) and the driver (probably) keeps the full voltage until the preset current is reached. Just a moment before that, the current is almost there, but you still have full voltage from the power supply. This is the theoretical worst case, but it applies only for a very short amount of time.
As soon as the current reaches the preset, the driver "cuts the voltage" to keep  2.4 ohm * 1.3 A = 3.2 V (because V = R * I). This means that the power supply sees 3.2 A/12 V*1.3 A = 0.35 A.
When running, the motors almost never start from zero to max current: both coils are powered and when one increases, the other one decreases.
In fact, the microstepping makes the steppers act more or less like AC motors with two phases. This means that overall the current is the max current per phase multipled by sqrt(2). Also, when using microstepping one phase (coil) is not completely shut off, but two of them work at the same time (with different current levels). This means that in total one compensates the other, and the power supply only provides, more or less, 0.35 * 1.4 = 0.5 A per stepper. You have two, so it's 1 A total, therefore 2 A PSU considering the inefficiencies.
A very easy and complete explanation is provided
here
:
By controlling the duty cycle of the chopper, an average voltage and
  an average current equal to the nominal motor voltage and current are
  created.
...
As the current increases, a voltage develops across the
  sensing resistor, which is fed back to the comparator. At the
  predetermined level, defined by the voltage at the reference input,
  the comparator resets the flipflop, which turns off the output
  transistor. The current decreases until the clock oscillator triggers
  the flip-flops, which turns on the output transistor again, and the
  cycle is repeated
So you never have coming out of the PSU more than the preset current.
Supply current is not the same as the motor current in a copper drive
. It is the motor current multiplied by the dutycycle, at
  standstill typically Isupply = IM · ( VM ⁄ Vsupply )
...
Depending on
  how the H-bridge is switched during the turn-off period, the current
  will either recirculate through one transistor and one diode (path 2),
  giving the slow current decay, or recirculate back through the power
  supply (path 3). The advantage of
feeding the power back to the
  power supply
is the fast current decay and the ability to quickly
  reduce to a lower current level.


Question:
I have the original Prusa i3m3 printer.  Prusa recommends cleaning the bed before each print with isopropanol (isopropyl alcohol), with only occasional cleaning with acetone.  The textured bed prohibits using acetone.

Given the SARS-COV-2 situation and COVID-19, isopropanol is impossible to find, and will not be in stock on shelves in the US for months.

What would you suggest as an alternative that might still be found on store shelves?

Answer:
Ethanol
(Ethyl Alcohol) should work just fine as long as it's around 80% or more. It's very similar to isopropanol as a cleaning solvent. What you're basically doing is removing any stray grease from the bed with a solvent that evaporates quickly.
Methanol
would also probably work. It's very poisonous though, and shouldn't come into contact with your skin, so it requires a bit more careful handling. Methanol also has the benefit that it can't be used for hand sanitizer (since it's absorbed through the skin), so supplies shouldn't run out.
Look for alternative sources, for example, methanol is often sold as de-icing agent for pneumatic brakes on trucks. Just make sure it's pure alcohol without anything funky added.


Question:
I work with Fusion360 for designing lots of things. Recently I learned how to work with parameters that I can easily modify all at once, allowing to pretty much make easily customizable pieces.

Now, Thingiverse wants customizer pieces in the shape of .SCAD files, and some people just can't work with Fusion360 (.F3D) or proper .STEP files that can be imported by most CAD programs.

I have no experience with OpenSCAD. Can I import my .STEP into openSCAD, retain my parameters and export it as a .SCAD, and if yes, how?

Answer:
No, you cannot import STEP nor Fusion360 files in OpenSCAD.
OpenSCAD
currently supports
:
3D formats
STL (both ASCII and Binary)
OFF
AMF [Note: Requires version 2019.05]
3MF [Note: Requires version 2019.05]
2D formats
DXF
SVG [Note: Requires version 2019.05]
Other
CSG can be imported using
```
include<>
```
or loaded like an SCAD file, PNG can be imported using
```
surface()
```


Question: I'm new to 3D Printing and recently purchased an Ender 3D PRO I'm having an issue with the filament guide tube getting pushed out of the nozzle on the feeding mechanism.  The assembly instructions don't include a whole lot of detail about installing this guide tube but there are blue clips that were included along with the spare nozzle.  There are no instructions on where to use these blue clips and I have a hunch this might be the problem.

Answer:
The blue clips stick in the connector on the extruder end of the feed tube. They are to keep it from opening as the printer extrudes and retracts filament.
To install them, push them in between the white part of the fitting on the feed tube (not the hot end). You should only need one or two, and they are all of varying thicknesses. If you're not familiar with these fittings, I found a
YouTube video
on how to use them.


Question: Recently my RAMPS power connector caught fire while heating the heated bed. I suspect this was a defect caused by the connector, and de-soldered/removed it as best I could. I'm  not an electrical engineer, so I'm looking for advice on whether It is possible to re-solder the power connectors directly onto the board, or I'm just risking another fire. Here are pictures of the top and bottom.

Answer:
The blue clips stick in the connector on the extruder end of the feed tube. They are to keep it from opening as the printer extrudes and retracts filament.
To install them, push them in between the white part of the fitting on the feed tube (not the hot end). You should only need one or two, and they are all of varying thicknesses. If you're not familiar with these fittings, I found a
YouTube video
on how to use them.


Question: Would it be posible to design something that is as flexible and that can be printed with PLA that would work as a cloth? I did some research and found that there was a company named Electroloom but that didn't make it. I'm not looking for anything fine, just something that would work for wiping

Answer:
Maybe you would be better off with TPU or some other type of flexible material...
I have been able to print PLA and have it flex quite a bit, but that was an ~0.2mm single layer print, I guess maybe up to 0.3-0.4mm should still be a little bit flexible, but not much. Also since you want it to wipe things, maybe you should look if TPU even has all the properties required for that as Carl mentioned in the comments.


Question:
My printer is calibrated for a certain clearance from the heated bed, which is chosen based on PLA.

I would like to try to increase it for the first layer for PETG, so that adhesion is reduced. The printer has M5 screws with 4000 steps/mm, so the resolution clearly allows that.

I don't want to modify the printer, I would like a G-Code or another option that I can apply in Prusa slicer in association with the specific filament when desired. I don't want to change the flow rate of the first layer, only the "zero" distance.

How can I do that?

Answer:
Maybe you would be better off with TPU or some other type of flexible material...
I have been able to print PLA and have it flex quite a bit, but that was an ~0.2mm single layer print, I guess maybe up to 0.3-0.4mm should still be a little bit flexible, but not much. Also since you want it to wipe things, maybe you should look if TPU even has all the properties required for that as Carl mentioned in the comments.


Question: Specifically using stainless steel nozzles, but I guess it's worth knowing about brass too. Is there any reason to be concerned about dimensional accuracy of the nozzle or anything like that as a result of repeated heating with a butane torch?

Answer:
If you carbonize the filament or other particles that are clogging the nozzle, then you will never get them clean. In my experience, it's not worth cleaning the nozzle with anything other than cleaning filament. If that doesn't work then change the nozzle. Heating the metal nozzle with a torch will change the temper of the material. I used to try cleaning with a soldering iron; which was to no avail.
Purchase a dozen brass nozzles and save your self the headache. Either that or a good quality set of stainless steel ones. They are easier to clean with the cleaning filament and aren't ablated by the filament as quickly, allowing for better dimensional accuracy over multiple prints.
https://www.amazon.com/eSUN-CLEANING-Filament-Printers-Cleaning/dp/B00MVIYNFW/


Question:
I'm having some issues with my Prusa i3 prints. I'm trying to print the default beer opener print that came with the Prusa's memory card but the infill will break causing clogging and now allowing the print to finish. I've attached a picture of one of the failed prints.

I've checked Prusa's website and tried tightening the extruder gears and made sure the gears are clean. I'm using the PLA sent with the printer (1.75 mm) and with a default G-code file so I'm fairly sure it is a hardware issue, but I'm not sure what the issue could be.

Here is the link that I've used to help me troubleshoot.

Answer:
If you carbonize the filament or other particles that are clogging the nozzle, then you will never get them clean. In my experience, it's not worth cleaning the nozzle with anything other than cleaning filament. If that doesn't work then change the nozzle. Heating the metal nozzle with a torch will change the temper of the material. I used to try cleaning with a soldering iron; which was to no avail.
Purchase a dozen brass nozzles and save your self the headache. Either that or a good quality set of stainless steel ones. They are easier to clean with the cleaning filament and aren't ablated by the filament as quickly, allowing for better dimensional accuracy over multiple prints.
https://www.amazon.com/eSUN-CLEANING-Filament-Printers-Cleaning/dp/B00MVIYNFW/


Question:
PLA has a heat capacity of 1.8-2.1 J/g-K, while PETG 1.1-1.3 J/g-K. This means that each gram of PLA needs more energy to heat up. I assume no "melting latent energy", since we talk about plastics.

The density is about the same.

Still, printing speed for PETG is said to be kept at max at 60 mm/s, while PLA can easily go up to 100 mm/s.

Why is PETG supposed to be printed slower than PLA?

Edit: a link to a more recent question may be of interest: Power consumption of filament extrusion

Answer:
The density of PLA is around 1.25 g/cm³ and the density of PETG is around 1.38 g/cm³. When you're talking about the amount of energy needed to melt a particular
volume
(which is what your extrusion units are) rather than mass, you need to scale the heat capacities (with units of
$\frac{\mathrm J}{\mathrm g\cdot \mathrm K}$
) by the density to get
$\frac{\mathrm J}{\mathrm{cm}^3\cdot \mathrm K}$
. This brings their volumetric heat capacities somewhat closer: 2.25-2.63 vs 1.52-1.79 (about 47 % higher for PLA rather than your figure of about 62 %), but with PLA still higher.
You also have to account for heat loss to the environment. PLA is typically printed around 200 °C or 210 °C at most; PETG in my experience requires 250 °C to reach low enough viscosity to be printable at any speed. Assuming an ambient 20 °C, the rate of heat loss should be something like 25 % higher for PETG. So the hotend has that much additional energy needed to begin with.
Beside that, PLA is printed at temperatures where it's still extrudable and able to bond even if the temperature drops significantly below the nominal nozzle temperature (down to 180 °C, maybe even slightly lower), whereas PETG has trouble with increased viscosity and poor bonding right away if temperature drops.
Going broader still, PETG seems to need to keep its heat longer after being extruded in order for layers to bond well. (As evidenced by the need to lower fan or turn it off completely.) A slow-moving nozzle both provides heat (from the proximity of the nozzle itself) to slow the cooling, and reduces air flow across the part (by not causing as much air flow itself just by moving).


Question:
I have two options - to buy either the Ender 3 or the Mega Zero. I'm heading towards Ender 3 because the Mega Zero doesn't have a heated bed.

My question is, how is a printer without a heated bed (the Mega Zero) a better option than one with a heated bed (the Ender 3)?

Why would I even consider buying a printer without a heated bed when the Ender 3 can do the same things and has a heated bed? I want be able to print not only PLA but other materials as well. Doesn't the Mega Zero limit you to using only PLA?

Answer:
Lack of a heated bed does not necessarily limit you to using PLA. I would say (among those I've used) the material that's least sensitive to whether you have a heated bed is probably TPU. Depending on your model, it can even be hard to print PLA without a heated bed, unless perhaps you're willing to use a brim or raft. Printing ABS or ASA without a heated bed is almost certainly out of the question, and PETG
might
be possible, but I'd expect it to be difficult.
Mechanically, the Anycubic Mega Zero looks very similar to the Ender 3. The claimed bed size on the Mega Zero is slightly smaller (220 mm vs 235 mm) but they might just be counting the usable part.
The only possible objective advantage to the Mega Zero I could find is the double gear extruder, which may help with printing faster or flexible filaments.
Presumably you could add a heating element to the bed if you want.


Question:
The heater cartridge on my CR10 V2 broke so I ordered a new one(12V). After replacing it the new one heats of very quickly past the target temperature and the slowly decreases to the target. Once it hits the target temp it goes up and down by 10 °C or so during prints. During the prints there is under extrusion. I read that if the filament gets hot too high up the hotted it could cause clogs. I replaced the nozzle as well and cleaned out everything.

Some things that I think may have an effect:

Could the new heater cartridge not be compatible?

does a poor solder job with heater cartridge wires have an effect

It's possible I messed up the thermistor when replacing heater cartridge, could that explain whats happening?

Is there anything else in the hot end assembly such as fans that would cause this?

Answer:
This sounds as if you have bought an incorrect heater element, e.g. one for 12 V instead of 24 V. The CR-10 uses 24 V. The 12 V cartridge has a lower resistance, so when powered by 24 V, the current is much higher and therefore also the heating power (
$ {(\frac{24}{12})}^2 = 4 $
times higher). For details on the calculation, the
this answer
on question:
"PID autotune fails 'Temp too high' with 12 V heater cartridge but works with 24 V?"
. This makes the hotend heat up very fast resulting in a large overshoot. You need to replace the cartridge for one for 24 V.
Note that I recently experienced exactly the same problem by mixing up the cartridges see
this answer
.


Question:
Does a filament exist that can resist ozone (like certain silicone tubing's can). Most glass bottles come with tin or plastic screw hard tops and I would like to replace the screw caps with something that is more resistant to ozone.

The reason for this is I make my own homemade ozonated oil in glass bottles and I would like to print out different hard screw top caps for some of the bottles.

Answer:
If making your own caps ends up being the best solution, TPU (thermoplastic polyurethane) is probably your best bet. I don't have specific information on printed TPU filament and ozone, but TPU is widely regarded as one of the most chemical-resistant materials you can easily print with, and
this page by Ozone Solutions
rates polyurethane (no mention of specific types) A/Excellent described as:
Ozone has
no effect
on these materials. They will last indefinitely.
Being at least slightly flexible, TPU will also yield a good seal without any additional gasket. You should probably choose an unpigmented "natural/clear" TPU filament in case the pigments do react.
It might (probably would) also work to coat an existing cap with polyurethane. I'm not sure how you'd best get it to adhere, but lightly sanding the plastic then using a spray in multiple coats is what I'd try first.


Question:
I've found many Youtube videos of makers upgrading to BLTouch sensor.

I have a Creality CR-10S Pro, so far bed leveling hasn't been an issue (after some days of trial and error).

My question is what are the problems/issues users need to face in order to need (or justify) an upgrade?

Answer:
I don't know your printer but I don't have BLtouch, and I have to set the height every time because the bed expands with heat.
If you print at variable bed temperature (PLA, ABS, PETg, nylon require different values) then that sensor helps a lot.
BL touch can also speed up bed calibration: you scan the bed, see the values to be corrected, adjust the bed without having to guess (given the thread pitch and required correction).
Also, if you print only in the center it's easy but if you print fully using the size of the bed, I doubt you can get very flat bed. The BLtouch helps for that too.
Also, there are clones like 3D touch which were tested and work equally well. Depending on your budget, they may be an interesting alternative.


Question:
I am curious, what is the purpose of printing a single-height outline around the objects to be printed?

Also, how would it affect the outline if the object to be printed extends to (very near) the very edge of the print area?

Update, I received a hint that an existing question has the answer; that link was not really to my satisfaction -- but it did link to another one that did: What are main differences between rafts, skirts and brims?

Answer:
My understand is that's is basically a purging extrusion, so that you get flow through the extruder before you start printing the object, as filament that's been inside the hotend during warm-up might have been "overcooked" by spending too much time in the hotend at temperature. It also helps stabilise the PID loop controlling the extruder temperature by allowing the PID loop to stabilise the temperature of the hotend as it's got filament flowing through it compared to it being idle.
It also shows the user where it intends to start printing, which is a useful check if something went wrong with Gcode generation.


Question:
Are there any defacto standards for interfacing between common 3D printers and custom extruders or other tooling? I was thinking how it would be good to have switchable nozzle widths mounted on the same heat block and switched between using a solenoid so you could have say a 0.25 mm for surface layer and details, then swap to 0.6 mm for the infill.

What would be the path of least resistance so it could be accessed in generic firmware?

The design I was thinking would be similar to a generic aluminium heat block with two nozzles screwed in side by side with there inputs meeting in an inverted Y junction with its center drilled out and replaced by a rod with appropriate channeling to divert the already molten plastic between nozzles. Turning the rod would be done from a solenoid mounted somewhere behind the heat-break.with a clamping mechanism.

Answer:
Generally: nozzles are not changed, the whole tool head is
While "tool change" is easy to implement in a G-code and could be easily adapted in the firmware, there are several practical issues to hot-swapping nozzles without swapping the whole hotend assembly:
The hotend is a fluid-dynamic system that needs to be sealed to operate under pressure and temperature.
The seal of the nozzle-heatbreak system is in most systems a metal-on-metal pressure seal
Rubber seals are not an option in a system that runs over 180°C
Moving metal seals are very hard to make and run smoothly.
Your idea: especially
No
There is literally no way to design a turning Y-switch that fits the following bills:
sealed
filament path ~2 mm
screw-in diameter for heatbreak and nozzles M6
creates enough free space between the lower outlets to mount 2 M6 nozzles with enough space to hold a wrench (=15mm diameter of centers)
fit into the form factor of a conventional heater block
Your idea would need to be considerably larger, need a stronger heater element and creates an impossibly to clean area around the turning junction peg. Atop that, you would trade 1 area of possible leak (between heatbreak and nozzle) for 3 areas of possible leaks (nozzle-block and heatbreak block) and one area of guaranteed leak (the turning peg).
How is it done then?!
Currently, there are the following ways to swap between different of nozzles mid-print that have been proven to work somewhat reliably:
fixed independent print heads with independent carriages.
fixed independent nozzles and heaters on one carriage.
swapping print heads on one carriage.
The first design is used for example in the Leapfrog Bolt, combined heads are for example the
e3D Chimera, Cyclops and Kraken
. e3D also designed on a reliable printhead - or rather tool  - swapping system starting about 2018 and did release it to the public in
late 2019
.
Type 1 needs you to level the printheads well and to the same height in the easy case, but with the right setup of firmware, a Z-offset of the two tools can be included and compensated for - possibly even automatically. Type 3 does usually demands you to include very accurate offsets of the used tools or includes a way to measure the offset during operation, though I lack insight into how e3D solves it. Both setups can mitigate oozing of the unused nozzles out of the printing volume.
Type 2 not only demands hyper exact leveling, but it
also
is very prone to create some sort of oozing of the unused nozzle.


Question:
I recently purchased a BIGTREETECH SKR mini E3 V1.2 and need to adjust some of the settings in configuration h to accommodate for my custom built 3d printer. In the past I've used the RAMPS 1.4 board and adjusted the firmware in the arduino IDE. What is the best way/recommended way to do this for the mini E3 V1.2.

Thanks.

Answer:
Basics
Firmware can be distributed in 2 ways:
As a compiled file (for example as .hex).
As an uncompiled repository (as in a preconfigured marlin distribution) that needs to be compiled at the users' side.
compiled file
Compiled files
can't
be altered easily. The only way to change settings after installation is to send the correct commands via a
console
to alter the settings in the SRAM then save the new settings into the EEPROM via
```
M500
```
from the
M50X family of commands
- and hoping that EEPROM was activated in the firmware to begin with.
uncompiled distribution
To alter an uncompiled Repository, you can follow the basic path in
Updating Marlin Firmware - Step by Step Guide


Question:
I'm new to printing resin miniatures for Dungeons & Dragons and most of my prints are successful, i.e. one or more miniatures print as expected.

However when I have multiple minis on the build plate the one in the middle works okay but the ones on the edges don't adhere to the build plate.

Should I limit myself to one or two minis in the center of the build plate? Or should it work and I just need to get my settings correct?

Note I'm using a Beam 3D Prism printer.

Answer:
You can definitely print full build plates of minis. You just need to find correct settings. If nothing sticks to the build plate - then you should increase bottom exposure time. Also check if the build plate is even. You can also sand your build plate a little bit to make adhesion better. Additionally, print with lower print speeds to increase success.
Finally, if your FEP is worn out and scratched or hazy, you should replace it.
I own a company producing 3D printing resins. We also write extensive printing guides from time to time. You can read more on finding correct settings in this
article
of mine.


Question:
I’m new to 3D printing and have the Creality Ender 3 Pro. I work a lot with clay for earrings and wanted to design my own cutters with a sharp edge to create clean shapes.

I use PLA and have been using the speed and nozzle (0.4 mm) that was already set when I bought it. It’s been creating fine edges but I’d like to make it a lot sharper. Using the instructions from videos I saw online, I created the following "U" shape (extrusion of .5 mm Is the “cutting edge”. I started getting some weird bubbles too and am not sure what has created that either (see pic).

I use Fusion 360 to make the cookie/clay cutter and then send it to Ultimaker Cura to slice.

Any help with how to make it sharper and more clean cuts would be great!

Answer:
An extrusion width of 0.5 mm is too wide for making a sharp outline, I do use this sometimes for extrusion width for the infill.
Note that you can sand plastic (e.g. PLA or ABS) to sharpen the edge.


Question:
I have an Ender 3, I got a new glass bed, the bed comes with glue on the back.

Should I stick the glass bed to the aluminium base? or just use it with the clips?
I saw other people just use the clips, but my glass seems to have a sticky back...

Answer:
Yes, the Volcano or the Super Volcano allow for larger flow rate (typically when using larger nozzles), that is where they were designed for. Just the nozzle will not help you, you need this larger nozzle shaft to be inside a Volcano heater block, else you cannot transfer the heat.
According to measurements from Metaform, the volumetric flow of a Volcano hotend is larger than the regular E3D V6 hotend.


Question: My printer is ignoring the "Z offset" setting in Cura and the "Bed Z" stored in the printer LCD settings? It has been working before but after a firmware update of my printer, it doesn't work. Even after flashing the previous firmware back "Bed Z" changes no longer affect anything. No matter if I change "Bed Z" during prints or if I use the "Z offset" option in Cura, the nozzle still prints at the same height.

Answer:
I have the same problem. You need to check your G-code to detect where's the problem.
Try comparing the G-code file with different values of the Z offset.
In my case it looks like this:
No offset
```
```
;LAYER_COUNT:107
;LAYER:0
M106 S255
G1 F300 Z0.84
G0 F6000 X124.645 Y78.208 Z0.84
;TYPE:SKIRT
G1 F300 Z0.44
G1 F1500 E0
```
```
With offset (comments made by Cura)
```
```
;LAYER_COUNT:107
;LAYER:0
M106 S255
G1 F300 Z2.06 ;adjusted by z offset
G92 Z0.84 ;consider this the original z before offset
G0 F6000 X119.093 Y42.498 Z0.84
;TYPE:SKIRT
G1 F300 Z0.44
```
```
I hope this helps.


Question:
I have this CTC i3 printer; when I print square test prints, as it moves along the Y-axis back to zero (front). It extrudes lines but very thin or none at all.

But opposite direction along the Y axis is 100 %

Answer:
Clearly you're having an extrusion problem. Extrusion problems usually come either from a clogged nozzle (as @Adam S. said) or from the extruder it self. To determine where the problem is located I would first do a flow rate test using
this
. When doing this test you can determine if the extruder is grinding the filament or if it's not grabbing it too much. After the calibration of the flowrate you can be certain that the printer is (by .gcode) pushing the correct amount of filament. If the problem persist I would first do an unclogging (since it's cheaper than the following option) using something like
this
.
If both previous options do not solve the problem, I would highly recommend you to by a mk-8 like metal extruder. After a while, the plastic one that comes with the printer loses force and you'll lose steps. Personally, I had a similar problem where the first layer was printed in a droplet pattern and was solved by changing the extruder to a metal one.
Try these options and if the problem persist you could upload some pictures of the first layer or a video. Other possibilities I think of are that the filament is having trouble passing through the Bowden tube or maybe you'll have to reasemble the hotend.


Question:
When I have overhangs in my model, Cura colors them red. However, I noticed if I make layer thickness thinner, the red area is reduced or disappears.

This could mean that thinner layer thickness is better for overhang, but it could also mean that a larger ratio of line width to layer thickness is better. It makes sense that if line width is 4X the layer thickness (such as 0.15 layers with 0.6 line width), overhang performance should be better than if line width is only 2X (such as 0.3 layers with the same 0.6 line width.

Is there a model that explains the optimum ratio of line thickness to layer height? Is only the ratio important, or is layer height also important by itself?

Answer:
In terms of Cura's model for showing overhangs, I'm nearly sure it's just the ratio - rise over run, or rather run over rise. And indeed that's what makes sense mathematically:
At least some portion of the wall extrusion in layer N+1 needs to sit on top of the corresponding wall extrusion in layer N. For a given 3D surface slope, the "run" - the distance the cross-section moves from one layer to the next, which needs to be bounded by some fraction of the line width - varies proportionally to the "rise" - the layer height.


Question:
From what I understand, UV curing of resin prints works by starting a chemical reaction that hardens the resin permanently.

Also, a curing step after print is needed to speed up the print and also to reduce the curing during print, which would cure resin beyond the current layer.

However, what is the transmissivity of UV light in partially cured prints? If I print a more massive object, or if I use an opaque resin, how deep will the object harden properly? Absorption is always exponential, meaning that it decreases quickly with depth.

Depending on the resin, how thick prints can be effectively cured? This information is not provided with the resin, which I actually would expect from reputable manufacturers.

Answer:
In terms of Cura's model for showing overhangs, I'm nearly sure it's just the ratio - rise over run, or rather run over rise. And indeed that's what makes sense mathematically:
At least some portion of the wall extrusion in layer N+1 needs to sit on top of the corresponding wall extrusion in layer N. For a given 3D surface slope, the "run" - the distance the cross-section moves from one layer to the next, which needs to be bounded by some fraction of the line width - varies proportionally to the "rise" - the layer height.


Question:
Currently, I'm using a Creality printer to print PLA (that's what I have on hand) but I'm definitely interested in working with other materials that require higher temperatures (both much higher, and just enough higher that the stock hotend is very marginal) in the future.

I understand that all-metal hotends are less forgiving and that they particularly are not the best for printing PLA, and shouldn't be assumed to be an upgrade when only printing PLA.

What I don't understand is, how bad are they? Are they so bad that I should plan on changing back to a PTFE hotend whenever I print PLA or ABS? Or are they suitable for use on a printer that is sometimes used for printing PLA and ABS and sometimes printing high-temp filaments?

Answer:
Are they so bad I should plan on changing back to a PTFE hot end?
No, all metal hot end are not that bad, and may even be beneficial when printing at higher temperatures. You mentioned that you want to print ABS and other such materials. At temperatures this high, my understanding is that the PTFE tube in the hot end may melt, or at least become so damaged that the hot end is blocked, leading to needing to replace the tube. My first 3D printer used a PTFE ho tend, which due to the printing temperatures I was using, and lack of knowledge of the many types of hot end, the tube got damaged after about 2/5 hours, leading to me needing to replace the tube. I eventually sent the printer back, got my money back and got a printer with an all metal hot end. That has never failed me in hundreds of hours of printing.
Are not the best for printing PLA
I have never had a problem printing PLA with an all metal hot end, however if you are printing just PLA, a PTFE hot end would be just fine, although not as versatile if you wanted to try different materials in the future.
In Summary:
Provided you print fast enough (I regularly print at 60 mm/s) to ensure that no filament cools down in the hot end you should be fine.


Question:
Typically in Arduinos, most of the 5 V outputs that have a limited amount of current (40 mA).

Are there any 3D printer boards, or is there even a more usual spot, where you can get a 5 V output that isn't capped by the microcontroller?

I know that USB 2.0 is (typically) limited to 500 mA especally when connected to a laptop. Just wondering if there was a way to for e.g. get a 200 mA output from one of the 5 V pins, or more if there is a stronger power supply connected to the USB port.

Answer:
Any pin that is labeled as "5 V" can supply the full amount of current. Looking at, for example, the
Arduino MEGA pinout
, we can see several pins labeled in red with "5 V". These are the pins you can use. Most 3D printer boards will expose the 5 V pins at several points. For example, the endstop connectors often have a 5 V pin that can be used.
The pins that are limited to 40 mA that you are thinking of are the digital pins, i.e. the pins that can be switched on/off by the microcontroller. These are actually more limited than this, and while in some cases drawing 40 mA from them may be possible, it is not a good idea.


Question: I want to be able to control my FLSUN QQ over Wi-Fi and don't have OctoPrint or a Raspberry Pi to run it on.

Answer:
Assuming you use Ultimaker Cura to slice, there is a MKS plugin that allows connecting to the MKS WiFi module that comes with the QQ. Just follow these steps:
Install the MKS WiFi Plugin
Open Cura
Click "Marketplace" in top right
Select "Plugins"
Scroll down to find the "MKS WiFi Plugin"
Click on the plugin.
Click "Install"
Restart Cura (quit and reopen)
Configure WiFi
Turn on your QQ
Tap Settings
Tap WiFi
Enable WiFi
Note the IP address and network name
Connect your computer to the printers network
Open your browser
type the IP address of your printer into the address bar
hit enter
Scroll down to "WIFI Configuration"
Select STA
Enter your home network SSID into the field labeled "WIFI"
Enter the password into the field labeled "KEY"
Click configure and reboot
Setup your printer in Cura
Open Cura
Open settings > Printer > Manage Printers...
Click "MKS Wifi"
Click "Add"
Enter the new IP address of your printer (can be found by opening WiFi settings on the printer)
Click Ok
7, Click connect.
Now you should be connected to your printer. After slicing you should have the option to "Print over FLSUN..." In the Monitor interface you should have some other options such as sending commands to the printer, and printing any files already on the SD card, as well as uploading gcode files to the SD card.
Happy Printing


Question: Is there any DRM or license management solution for 3D printing? I'm looking for something, that would help me limit the number of prints someone can make from my projects. Basically, I would like to sell the "right to make no more than X copies" of my design. I don't expect it to be bullet-proof (like Widevine L1 for video), but it should at least help me with license management.

Answer:
Good luck with that.
Issues you will face:
using a G-code editor (or built-in printer software) to create multiple copies of the object in a single print session
user writing the printer file to an SD card, then block-copying the SD card
defining a "print". Specifically:
is #2 another functional copy of the object, or did #1 fail? Failed prints happen a lot.
is #3 another functional copy of the object, or was #2 damaged in post-processing? Like removing supports or left it in the acetone 5 seconds too long and it's now a blob.
is #4 another functional copy of the object, or was #3 tossed because the guy running the printer grabbed the wrong spool and made a perfectly good print in the perfectly wrong material/colour.
is #5 another functional copy of the object, or was #4 damaged in shipping?
The whole process is one-way. There just isn't a path for anything other than the end user to know what they pulled off the print bed. Unless you make the entire process from design software to printer you won't change that. And good luck selling it, 'cause the user base is rather strongly opposed to that kind of thing. For example, ANY kind of DRM in the product, from printer software to filament, is an immediate no-buy for me. I don't care if you are paying me to take it, I will find an alternative without that particular annoyance. And no, I don't use Microsoft or Adobe products either.


Question:
I recently heard that the 3D printing lab at my college can do fused-deposition with ABS and PLA, but I would like to use TPU, for greater flexibility.

Is it possible to feed a TPU filament into the same machine built for ABS/PLA? Or is there no difference? Assume the diameters of the filaments are the same.

Answer:
Most printers can print most filaments. However, some more exotic filaments are not suitable for all printers:
To print a flexible filament such as TPU, the filament path from the extruder needs to be well-constrained. A bowden extruder is generally less good at handling flexible filaments than a direct extruder. Some direct extruders without a well-constrained filament path may also be unsuitable.
A printer without a heated bed won't be able to print filaments that tend to warp such as ABS.
A printer without a (heated) enclosure won't be able to print filaments that tend to warp
a lot
such as polycarbonate
A printer with a PTFE-lined hotend won't be able to print filaments that require higher temperatures. PETG is at the upper end of what can be (safely) printed with a PTFE-lined hotend, while filaments such as polycarbonate require temperatures well outside the usable range.
A printer with a standard brass nozzle won't be able to print (not long, anyways) abrasive filaments such as glow-in-the-dark.
It is likely the printer at your lab will be able to handle TPU just fine. If it is a bowden printer then you might have some difficulty printing but it might still work depending on exactly how soft the filament is and how well-constrained the filament path.


Question: If I have an issue with my FLSUN printer how can I contact customer support?

Answer:
I have had good luck contacting them via AliExpress
https://flsun.aliexpress.com/store/2383013
even though I bought my printer on Amazon.


Question:
I find that white filaments are quite translucent and printing 5 layers of white filament onto 2 layers of black filament (at 0.2 mm layers, the white layers being 100% infilled and the underlying black layer covering about 85% of the whole area) produces a slightly grey color on the top.

Is that a limitation of the white colour (or the actual material used)?

Are there materials, that address this issue to some extent?

Adjusting layer thickness while keeping the overall height won't change things, right?

Answer:
This could be caused by under extrusion, often caused by the bed being too close to the hot end / extruder nozzle. You could try to relevel the bed, or change the screws so that the bed moves down slightly. Often when levelling, you want to feel slight resistance when sliding a piece of paper between the bed an the nozzle. You should do this for all 4 corners. Be careful though, you dont want the bed too far away from the nozzle, or problems maybe arise with the print not sticking to the bed.
Hope this helps, Luke.


Question:
I installed a BLTouch bed leveling probe on my printer which uses Marlin 2.0.5.3.

Now the printer seems to be of two minds when it comes to finding the origin. Homing XY moves to the lower left as it always has, but homing Z moves not only to Z=0, but also to the center of the build plate. The printer knows this is (100,100,0) and is not mistakenly thinking it is (0,0,0).

This causes some issues such as now the nozzle wipe at the beginning of a print happens right in the center of where the print is supposed to be.

Is this expected behavior?

Answer:
This is a consequence of enabling
```
Z_SAFE_HOMING
```
:
Z Safe Homing prevents Z from homing when the probe (or nozzle) is outside bed area by moving to a defined XY point (by default, the middle of the bed) before Z Homing when homing all axes with
```
G28
```
. As a side-effect, X and Y homing are required before Z homing. If stepper drivers time out, X and Y homing will be required again.
Enable this option if a probe (not an endstop) is being used for Z homing. Z Safe Homing isn’t needed if a Z endstop is used for homing, but it may also be enabled just to have XY always move to some custom position after homing.
My default Cura start G-code contained this sequence:
```
```
G28 X0 Y0 ;move X/Y to min endstops
G28 Z0 ;move Z to min endstops
```
```
I changed this to
```
```
G28 ;safe homing
G90 ;absolute positioning
G0 X0 Y0 ; move to bottom-left corner for nozzle wipe
```
```
However any oozing will still happen at the center of the build plate, which is a problem.


Question:
My Ender 3 LCD display was working ok, I went to turn it on recently but is not showing any signal of life anymore...

I have tried unplugging and plugging again, is there a way to test if the screen still works?

What is the issue? Or should I just buy and install a new LCD?

Answer:
The fact that the bumps were in the same spots on multiple occasions points to z-axis problems. Turn your printer off and manually turn the z-axis all the way from bottom to top. If there are any tight spots, there is some
z-axis binding
. If there are no tight spots, skip to the last paragraph.
Try taking off the z-axis by removing the set screws (pictured below). Remember which side was pointing up for a later step.
Once you do that, clean the screw thoroughly with a brush, cloth, solution, or a combination of those. Put the screw back in the opposite way this time.
If you get no bumps, then it was indeed the z-axis
If the bumps are still there, try lowering your temperature some more(200 is still a little high compared to what I do for PLA), and
calibrate your e-steps
if you haven't already.


Question:
I have a few 3D printers and now want to start building a custom 3D printer.
I want to build a 3D printer with multiple nozzles, and I want to make the hotend thin so the nozzles can be closer together.
What is the thinnest nozzle avalible to buy?
Are there any guides or details on how I could make a custom nozzle or modify a nozzle if I can't buy a thin nozzle?

Answer:
The size of the nozzle usually isn't the main factor for how close you can put nozzles together.  To keep the filament drive gear system from being the limiting factor, you would need Bowden extruders. "Then, the heat sinks and fans would be your limiting factor.  Have you considered a single nozzle with three extruders?  Otherwise, you need custom angled heat sinks similar to the three heat sinks on a single nozzle, and still a way to orient the nozzles at the same Z-height.  That would be difficult if all the nozzles are on the same heater block.  It still seems that nozzle size is the least of the issues of putting nozzles close together.
If you search for smaller nozzle sizes, you will get nozzles with smaller openings, not smaller overall size.  The threads on the nozzles are a standard size.  Thus, the smaller opening size can't be put closer together than the larger opening size.  Otherwise, you have only small variations between different types of nozzles and need room to screw them in to the heater block if you put all of them into one block.  You can get a nozzle using a 6 mm hex wrench that is smaller than one using a 7 mm hex (E3D).


Question: I am building a medium-sized printer which needs to produce super-precise parts at a moderately fast print time. I frankly don't want to deal with belts or their tension issues but on the other hand, having ball screws on each axis will increase inertia...right?. I'm using Rexroth rails and will use (depending on what I decide) name brand belts or name brand ball screws.

Answer:
The size of the nozzle usually isn't the main factor for how close you can put nozzles together.  To keep the filament drive gear system from being the limiting factor, you would need Bowden extruders. "Then, the heat sinks and fans would be your limiting factor.  Have you considered a single nozzle with three extruders?  Otherwise, you need custom angled heat sinks similar to the three heat sinks on a single nozzle, and still a way to orient the nozzles at the same Z-height.  That would be difficult if all the nozzles are on the same heater block.  It still seems that nozzle size is the least of the issues of putting nozzles close together.
If you search for smaller nozzle sizes, you will get nozzles with smaller openings, not smaller overall size.  The threads on the nozzles are a standard size.  Thus, the smaller opening size can't be put closer together than the larger opening size.  Otherwise, you have only small variations between different types of nozzles and need room to screw them in to the heater block if you put all of them into one block.  You can get a nozzle using a 6 mm hex wrench that is smaller than one using a 7 mm hex (E3D).


Question:
I had filament on my 3D45 coming out of threads on the nozzle.

To fix this I removed the nozzle to find the PTFE Liner in really bad shape. It looked crushed and deformed. Now the tough part, how do I replace the PTFE Liner. You can't seem to buy the liner and getting a replacement nozzle assembly from Dremel takes weeks. Can anybody help me figure this out please, I really would like to get back to printing!!

Answer:
The initial problem you had with filament coming out of the threads at the nozzle is caused by improper seating of the heat break to the nozzle. In a "from the ground up" installation, you'd have an empty heat block, containing your heater core and your thermistor. Threaded into the "bottom" of the block is the nozzle, just a turn shy of being flush with the heat block. The heat break is the thin threaded segment extending from the heavily finned heat sink.
The heat sink/heat break combination is threaded into the heat block until it contacts the nozzle, at which time, the nozzle is snugged into place securely. This keeps continuous the filament path from the heat break to the nozzle. Somewhere in time, a gap opened between the two.
When you have assembled everything (including the PTFE liner), you'll want to heat the extruder assembly to about 250 °C and re-snug the nozzle to the heat block and heat break. Hold securely the heater block, as you do not want to apply force that will snap or otherwise damage the fragile heat break. Use a wrench that fits the heater block without contacting the wiring. Use a wrench that will keep your fingers safe, as the heat block will be hot.
Stepping back in time a bit, when you remove the assembly, you should be able to determine the necessary length for the PTFE tube. I checked the manual for your printer and it is lacking in detail for this information. The diameters you've specified are standard and you should be able to locate a suitable substitute from many online sources. Amazon, Matterhackers, eBay, etc.
Examine the heat break tubing. The diameter should not be so small as to allow you to push the PTFE tubing in from the heater block side, unless you have an unusually manufactured product. Dremel may have decided to create a new bit of engineering, but I'd expect not.
You'll purchase more PTFE than required and examination of the upper portion of the heat sink should give you a clue how much to use. When the cover of the extruder assembly is removed, is there a guide for the filament to make it easier to push through the PTFE tubing? If so, the length of the PTFE is from the bottom of the guide to the bottom of the bore of the heat sink/heat break assembly.
Photos of the upper entry to the heat sink/heat break, with the cover removed, would be useful, but you may have sufficient resources in hand to resolve your problem, once you replace the nozzle and purchase PTFE tubing of the correct size.


Question:
I'm printing 6 separate parts in one go, after 4 hours of printing one part failed, but the other 5 are printing nicely.

Is there a way to prevent the print from printing the failed part and continue printing the other 5 parts.

I'm using Cura and an Ender 3 printer.

Answer:
No, once you sliced the 6 parts on the build plate in your slicer, the G-code is fixed and the printer will print as the sliced instructions. During printing it cannot skip the code of a part that failed along the way; there is no way to interfere with the printing other than stopping the print. For that reason, many people don't pack the build plate too full, the more parts, the higher the chance it fails. You could print the part one after each other. Packing the plate with multiple parts is usually not faster than printing one at a time (if it fails you have nothing, otherwise a single failed print).
Depending on the size of the parts you can also tell the printer to print each part on the plate one after another in a single job; note that the printhead dimensions limit this. If one fails you stop the job, but the already printed parts are saved. You can then commence a new print of cut the G-code and reprint the shortened file.


Question:
Got my Ender 3 v2 and stack with the bed leveling.

Used default settings, Creality slicer 4.2, test PLA from the kit and print model https://www.thingiverse.com/thing:3013319 (4 squares in each corner and 1 in the middle), nozzle 200 °C, bed 60 °C.

After some adjustments, I have good solid pieces on the bed corners  but the center one has small gaps. Is it possible to fix this problem?

Corner pice:

Center piece:

Answer:
The gaps are, because the nozzle is to far from the bed at this point. It may sound like a big deal, but actually this is not leveling alone, but it looks like the bed is not a perfect plane/perfectly flat. This is normal, my ikea mirror and my stock bed show the same thing. Now here's one solution:
Print calibration stickers, like you already did on various places around the bed to get a feel, where it is too low. Let it cool and put painters tape (the very very thin tape, that should not burn) on areas, where the bed is too low. Print more calibration rectangles and check if you have enough. Repeat until you cannot see a difference.
It took me about 2h to level everything absolutely perfectly. This was 2 years ago and I didn't have to touch the tape below my bed ever since. It just works.
Alternative solutions involve mesh bed leveling and buying a new bed surface or even the surface below the bed. However, I found that to neither of them work reliably, whereas the simple tuning does what it's supposed to.