Update - 4 Feb 2019: This was originally modeled in SketchUp, which isn't parametric, and based on some of the comments, I redid the design in Fusion 360.The STL file "MPSMv2 threaded insert v2" is the new design, and I've printed it out and it seems to work pretty well. I've also included a GCODE file of this design sliced at a 0.219mm layer height in Cura - it only takes four minutes, so if your collet is broken already, you could conceivably stand there holding the PTFE tube in place during that short 4 minute print. I've also included the F3D file if anyone wants to see my work or modify it.
Note: I'm pretty happy with my design, and it does work, but it's not a long term solution. For a better solution, check out MPSM V2 Improved Extruder. My piece is something that you could print to get yourself back up and running if the stock top collet breaks, and then use mine to print out that better design.
Older Monoprice Mini printers had a brass locking collet for the PTFE tube at both ends. The newer ones have a very minimal one at the top that locks in place and seems to be cheaply made. Mine broke, so I return/exchanged the printer, and then I saw Bigben2 had the same problem with his and decided to see if I could replace that small, fragile, hard-to-find piece for one of the more standard brass collets.
What I have here is two options to accomplish the same purpose:
This piece replaces the original top collect with a printable piece that has an M6 thread so you can thread in the appropriate brass collet. You remove the two screws that hold the black plastic cap on the top of the extruder motor, remove the original collet and replace it with the printed piece threaded onto a brass collet. Because the piece is small, you might need to hold it with pliers as you thread in the brass piece. The threads fit a bit tight.
- Replacement top cap
This piece replaces the original collet as well as the top cap. Currently I have not added threads to this piece, but it is sized to allow an M6 brass collet to be threaded in directly without the need for
Either one of these works, I've printed and tested both.
- Thingiverse does strange things with Amazon links, so here's the URL for the brass collets that I purchased:
https://amazon.com/gp/product/B019RQ5EYE/ - copy and paste that.
- Barring the Amazon link, just make sure that you search for "quick connect 4mm PTFE fitting M6" to get the right item. You need something to fit a 4mm PTFE tube and an M6x1 metric thread. There are other threads available, but I sized for the M6.
- The bowden tube on my printer was a bit too long to begin with, and adding about 18mm with the brass collet makes it even moreso. You may with to shorten your bowden tube after installing this to address the extra length.
If you'd rather just have a spare of the original part, here's a link for a store that carries it:
Apologies if the orange hand spinner in the photos offends you... but if you want to print your own, it's right here.
Thanks to McMaster-Carr for the 3D STEP model of the M6 nut that I used for the threads, as I had trouble getting one from Nut Job
- MPSM V2 Improved Extruder
This design replaces the entire extruder base plate, block, and arm with new parts. I had considered something along this line as the next step but honestly this one looks way better than what I would have come up with. The use of the M6 steel nut should also make it more durable in the long term. If your original part broke, you could use my design to print out this one.
- 2018-02-15: I realized I was missing a piece from the extruder top cap which resulted in there being air space which made feeding the filament a little tricky. Removed the original piece and uploaded the modified piece. Have printed the updated piece and am currently using it.
I printed these at three shells and 20% infill.
With the smaller part, 3 shells means it's effectively 100% infill anyway.
With the larger part, 20% infill seems sufficient.
No rafts or brims are necessary, I had good results printing with just a skirt to prime the extruder.
I also didn't bother with any supports. The small piece is angled to address overhangs, and the small overhang in the larger part isn't big enough to cause a problem.