<h2>Backstory</h2>

<p>I've had issues in the past with my drive gear "eating" my filament. It seemed that the filament quit extruding for one reason or another and the drive gear would slowly eat away at the side of the filament.</p>

<p>I eventually assumed it was the plastic filament guides causing unnecessary tension that the drive gear couldn't compete with, ultimately keeping the filament from moving forward. Thusly, allowing the drive gear to continue "trying".</p>

<p>My solution was to hang my spools above the machine to avoid using the filament guides feeding from the back of the machine up through the top.</p>

<h2>Question</h2>

<p>Can the plastic filament guides really cause that much drag? What other variables can I expect to look out for?</p>

<p><em>Machine:</em> <strong>MakerBot Replicator Dual (1st Generation)</strong></p>

I have a few hundred printing hours on a Monoprice Dual Extrusion, which is essentially the same thing.  I've had a couple random issues that lead to filament stripping by the extruder motor:
Clogs (either a buildup of material over time, or from over-retraction)
Filament kinks around the spool holder
Some other restriction of the spool's rotation
I suspected the guides early on, but the grips on the rotor are actually fairly strong and the guide tubes are smooth enough to not cause a problem by themselves; I'd recommend looking at the other ends of the assembly first, as they're more likely to cause a problem.  If you preheat the nozzle, open the tensioner on the extruder stepper, and can't push the filament into the nozzle with your fingers, the motor won't be able to do it either.