<p>I'm quite new to 3D CAD and printing.
I own a Dremel 3D45 and I use FreeCad / Ultimaker Cura as softwares.</p>
<p>My question is pretty simple.
Say you have to make one object with a pin and another with a hole. They should be coupled together. Of course if you set the diameters of the pin and the hole equal the won't fit!</p>
<p>Right now I'm setting the hole larger of 0.2 mm and the pin smaller of 0.2 mm. This allow a quite good coupling (not so hard but with some resistance).</p>
<p>I guess this tolerance (0.4 mm in my example) depends on a lot of variables: 3D printer settings, material, etc... so it may change using different setup.</p>
<p>How to correctly handle this?</p>
<p>Should I add a variable in my CAD spreadsheet and use it to change the nominal diameter of the coupling items?</p>
<p>I don't think so, but anyway: is there a settings in Ultimaker Cura that allow to compensate an hole or a pin by a specified amount?</p>
<p>Any other suggestion is gladly accepted.</p>

I guess this tolerance (0.4 mm in my example) depends on a lot of variables: 3D printer settings, material, etc... so it may change using different setup.
Tolerances required
depend on the geometry you're printing
. A hole that is horizontal, vertical, or diagonal will need different tolerance (as I found out in a project that used the same steel dowel pins in three different orientations). And, vertical holes and pins are different from flat-sided shapes: the plastic will be pulled toward the center of a curve, so diameters come out small (and more so for holes since there's no material further inward to resist the movement).
That said, I think you can expect that the distortions of printing are fairly consistent, if your printer is functioning well. I have a Prusa i3 MK3S, and I have printed many parts other people have designed, and
when
those parts have been designed carefully, I almost always get very good fits between parts. So, my experience suggests that models do not necessarily need tuning for specific printers.
Should I add a variable in my CAD spreadsheet and use it to change the nominal diameter of the coupling items?
Yes. If nothing else, this allows you to define how the two parts
should
fit together separately for the printing error. Use separate numbers for different shapes/fits, so that you can adjust one without messing up another.