I got the rest of the hardware that I was waiting for in order to finish my bowden setup – a set of 608 bearings and some 100mm M5 threaded rods.  So last night, I went ahead and finished up the job.

For the gear reduction in the extruder motor, I used thing #338620 from Thingiverse, which worked out rather well. After putting the assembly together, I noticed the shaft for the M5 rod was a bit tight, so I used a 3/16” drill bit to widen it a tiny bit. Then I was able to slip it in freely, which is important so that the screw doesn’t bite into the shaft during rotation and drive itself out.

From there, I mounted the gear and used a couple of M5 nuts to space it properly so it would align with the smaller gear attached to the stepper when it’s assembled.  I also slipped in the hobbed gear onto the M5 rod.

I then mounted the 608 bearing with an M5 washer and a M3 10mm screw. You can’t really see it in this next picture, but I have a couple of M3 washers sandwiched between the bearing mount and the main assembly so that the bearing isn’t digging into the hobbed gear.  It turned out to be the perfect size for feeding the filament through – it grips very well with zero slippage.

I wrapped it all up by mounting it onto the extruder stepper motor… perfect fit!

I did end up making a quick and dirty bracket to mount the geared stepper assembly onto the body of the PrintrBot.  It was a quick job just to get the stepper off the floor.  I’m not really happy with it, but I have an idea for a better design, which I’ll work on this week. Here’s a shot of the complete bowden set up installed (ignore the possessed cat in the background)

I did end up running a print through and it turned out very well.  I actually did have a hot end jam while calibrating it, and something interesting happened. Rather than the extruder skipping or stripping the filament (like it normally does), it actually broke the filament in half and started extruding both broken pieces.  I’ve never seen this happen before – it’s a real testament to amount of torque that this 5:1 gear reduction is producing:

//Ken