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Minimalist MK8 Rework

by wjsteele, published

Minimalist MK8 Rework by wjsteele Dec 31, 2012
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I modified InfinityPlusPlus' MK8 drive to use a simple to acquire "Delta Faucet" spring and optimized the placement of the vias to allow the extruder to drive either 3mm or 1.75mm filament. It also includes recessed heads for the 3mm attachment screws.


1) Print both peices (optionally mirror the drive.)
2) Mount back to stepper with one screw in left hole (or right hole for left side extruders)
Note: Step #2 is optional... it works fine without this screw on most steppers due to the design being braced by the raised center portion of the stepper motor.
3) Remove spindle tower from inner portion of the bearing pressure arm.
4) Insert 623 bearing into slot and use 3mmx10mm screw from back to affix bearing. Make sure it turns freely. Trim if necessary.
5) Place arm on stepper with 3mm screw and insert spring.
a) For 3mm filament drive... use spring with small portion facing down.
b) For 1.75mm filament drive... use spring with rubber cap on small end facing up.
6) Tighten hinge screw to chassis.

Install as normal MK7 and start printing!

(BTW... the Delta Spring I purchased from Home Depot... here is a quick link to it: http://www.homedepot.com/h_d1/N-5yc1v/R-100169417/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=delta+faucet+spring&storeId=10051)

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Would you be wiling to try and modify this so that it would work with a Nema14 stepper. I would really be interested in testing this concept out, since I just got some new really hight torque Nema14s.

I don't personally have any NEMA 14s that would work for this.

Awesome, thanks. I was looking around Thingiverse and was very surprised when I didn't find any reprap mounts for direct drive extruders like this. Does everyone have a Makerbot?

Could you upload a mirrored version for those who don't use SketchUp.

Sure, I will tomorrow when I get back to the office. But you don't need Sketchup to do it... I just used ReplicatorG's mirror function to flip it.

I added both a "LEFT" and "RIGHT" version.

Has anyone tested this with 3mm filament and a .35 mm nozzle? Im interested in the results and the torque of your stepper.

I haven't tried it yet... I've only used .5 and .4 with mine... But they worked perfectly, so I wouldn't think old have much trouble as long as your NEMA 17 is torquey enough. I've used the MakerBot "Monster" extruder that they shipped with their MK6 as well as a 42 oz/in unit I got from QU-BD with no issues.

I liked this version because it uses the Delta faucet spring, of which I have way too many, it also uses a 623 radial bearing, which I do not currently have but will soon... in the meantime I printed some disks with the same dimensions and I was surprised by how well it's working.

I was also shocked by how quickly Sailfish wore down my stock plunger, and then slow to learn that all my trouble printing was due to the worn-plungers and not Sailfish! Those high filament feed rates really do scream for a bearing on the other side of the feed gear.

To all those who work the minimal MK8s- thank you!

Forgot to mention that I also used those leftover metal spacer / washers from the stock MK8 between the PLA hinge points on the arm... unquestionably frees up their motion.

Great idea... I'll add them to mine as well. The only thing to be careful of is the alignment of the bearing to the filament... A washer will force it a little further out. With 1.75 it might not be as much of an issue, but with 3mm, that alignment is critical.