Minimalistic Mk8 replacement

by emmett, published

Minimalistic Mk8 replacement by emmett Aug 9, 2012

Featured Thing!


The Minimalistic Mk7 replacement works so nicely, I wanted to put them on my Replicator as well. It required a slight redesign in order to fit under the piece that holds the guide tubes. I use 693 bearings on this, but you should also be able to use 623 bearings like on whosawhatsis' original.

I get much better prints with these than the stock Mk8s because they grip much better on a variety of filaments due to the compliance and there is much less friction thanks to the bearing. I was using Protoparadigm's PLA and having all kinds of problems with missing filament after reversals, but not anymore. No more lost steps or stripping on the extruders, and an added bonus is you can now clean the drive gear without disassembling the unit. Also, switching colors is quicker since you can just squeeze and pull instead of going through all that unload/reload filament business.

Recent Comments

view all

Anyone tried ninjaflex with this mod?

I did and I couldn't get the filament loaded, it kept squirming out the side.

Allegedly it should work. I guess I will try again when I've recharged my patience.

yessss i want them.

Hi Guido!
I'm very interested in your rep2 mod! I'd like to use it in mine if you don't mind of course =)

More from 3D Printer Parts

view more

Liked By

view all

Give a Shout Out

If you print this Thing and display it in public proudly give attribution by printing and displaying this tag. Print Thing Tag


You'll need a 693 or 623 bearing and a 3x10mm bolt for each extruder. Print these at 100% infill with zero extra shells. Rip the support out of the notch in the arm. Put the bearing in there and keep in place by screwing in the bolt (from the back, as in the head will face the motor).

Disassemble the fan/heatsink and remove the old extruder. Use the same mounting bolts to attach the two pieces of the minimal Mk8 extruder. Make it nice and tight and reassemble the fan and heatsink the same way. Cram a spring into the notches between the two arms. I used the same spring I used on the original minimal Mk7, which in my case was Utility Comp Spring C-614 (5/16 x 1-1/4 x 0.041 inches) I found at my local hardware store.


You must be logged in to post a comment.

s_p_e_x on Feb 16, 2014 said:

Anyone tried ninjaflex with this mod?

I did and I couldn't get the filament loaded, it kept squirming out the side.

Allegedly it should work. I guess I will try again when I've recharged my patience.

robokid on Mar 12, 2013 said:

I could only get the "#9657K331 Steel Compression Springs" in packs of a dozen, so if anyone wants a couple of them i'd be willing to sell em' off.

p.s. AMAZING mod, makes the replicator 1000 times better (especially when I need to change out the filament in a hurry.)

Printed_Solid on Feb 26, 2013 said:

Great upgrade! I ordered an extra pair of bearings and springs with mine, which I'm guessing I won't be needing. So if anyone needs one of these made, let me know.

Ubermeisters on Jan 23, 2014 said:

yessss i want them.

kalan on Jan 30, 2013 said:

Can someone make one of these for me. I Can't even get mine to work well enough to print them... I'll pay $50 obo and I'll pay for shipping if someone will help me out!

Claydiz on Jan 27, 2013 said:

What do you use to keep the bearing in?

rjschave on Jan 15, 2013 said:

Just in case anyone else has trouble with the springs from McMaster...

If you order the springs from McMaster (part # 9657K311), they will likely send you springs from WB Jones Spring Company. The part number from WB Jones is C-10-032-040. The specs for both part numbers specify an outside diameter of .300". The bag I received from McMaster had the correct WB Jones part number, but was full of springs with a .360" outside diameter (WB Jones Part # C-12-032-40). I called McMaster and they said they would send out a new bag of springs. They said they would measure the springs beforehand since the bags had the wrong part with the correct part number.

stnt on Dec 19, 2012 said:

I unclogged/unjammed my Rep2, no dissasembly required.

1.get a #6 nickel wound guitar string from the local guitar shop.
2. heat up the tip with a lighter for approx. 5 seconds.
3. plunge it in and out of the hole, when you do it correctly, you will feel the churningof the plastic that is obstructing your extruder.
4.insert the new pla reel and your done.

-note that this works better if you load your plastic in quickly after doing this without waiting much time for the warm up.

hope it helps.


andyways on Dec 11, 2012 said:

Finally installed these on my Replicator 1 after having the vitamins (metal parts) sitting on my nightstand for a few months.  
I used the same parts drandolph listed.Super easy to print, surprisingly easy to build+install!Thanks Emmett and whosawhatsits for creating the models.My only critique is that it is more challenging to load filament. It doesn't seem to guide the filament into the hotend as well as the stock MBI delrin plunger component.  Not a huge deal, and perhaps more usage with it will help me get a 'feel' for when the filament is properly aligned to the hotend nozzle.

emmett on Dec 11, 2012 said:

Yeah, I had the same problem at first. I've found it works much better to just squeeze the spring to get the filament caught between the drive gear and the bearing. Then I let go of the spring and push the filament down, letting the motor freewheel. It seems to go in much better that way. Of course it also helps to straighten the filament a bit first.

trobok on Nov 20, 2012 said:

I think this is what I have been waiting for! Anyone selling these as kits? My printer is not functioning well at all and  McMaster will not ship the parts to asia. Would love to try these out and not too sure where to look for parts here.

anewsome on Nov 12, 2012 said:

Ok, so here's a little more info. I was able to download the OpenSCAD file and make my own stl. That prints fine. The only problem is, the scad file is for Extruder left side. I need the right side for replicator 2. It doesn't seem like just flipping the parts on the platform will do the trick and I don't see any parameters in the scad file that I can change and get the right side instead.

If anyone has any idea how I can get this part either ready to print or get and stl or s3g file of the right side, I'd appreciate the help.

emmett on Nov 13, 2012 said:

 The only difference between left and right is one is the mirror image of the other. RepG can mirror things, and hopefully that's possible in MakerWare as well. If not, put a "mirror([1,0,0])" command in front of the top-level object in OpenSCAD, to get the other hand.

anewsome on Nov 12, 2012 said:

This looks like a really awesome mod. It appears to solve all the problems I'm having with extrusion on my Replicator 2. I am trying to print these parts to fix my Replicator 2 Extruder but after I downloaded the .stl file for ExtruderR.stl, I tried to slice it using the MakerWare app. When I try and print it, the print head moves to the center of the platform and then completes the build. Nothing gets printed at all. Is there something special I have to do in order to get this stl to print? As you can tell, I'm kind of new to this.

GuidoZelf on Nov 12, 2012 said:

I've just made one for the Rep 2, cutting away some plastic from the top cover of the exctruder to make room for the lever.
This works great: emmett Thanks!
If anyone is interested I have a few pictures of the (easy) mod I did to make this fit a Replicator 2 extruder.

Cadmy on May 23, 2013 said:

Hi Guido!
I'm very interested in your rep2 mod! I'd like to use it in mine if you don't mind of course =)

GuidoZelf on Nov 10, 2012 said:

Anyone experience with mounting a springloaded bearing solution to a Replicator 2?
The plastic cover seems to prevent mounting this fantastic Thing...

bottleworks on Oct 18, 2012 said:

This works great!  I bought the #7804K128 bearings from McMaster-Carr.  I feel the extra money spent is worth it. 

LiquidBeef on Oct 29, 2012 said:

I feel the same way.

kyle59 on Oct 14, 2012 said:

I used 2 precision bearings that came from an old 10th scale brushed RC car motor and my spring is 5/16 x 1-1/16 x 0.035? since that was the closest the hardware store had. and M3 x10mm button head allen screws. I recommend this upgrade to anyone with a replicator. 

Well done thank you Emmett! 

SparkySD on Oct 14, 2012 said:

I was having major problems with both extruders failing half way through prints. This mod has fixed the problem completely. Well done  emmett !

Thanks also to drandolph for specifying the McMaster parts. This saved a bunch of time figuring out what to buy :

1pk #9657K331 Steel Compression Spring Zinc-Plated Music Wire, 1.25" L,.300" OD,.032" Wire(12 pack)http://www.mcmaster.com/nav/en... 
2pcs #7804K128 Miniature HI-Precision SS Ball BearingABEC-5 Double Shielded, for 3 mm Shaft Diameter, 10 mm ODhttp://www.mcmaster.com/nav/... #92855A310 Metric 18-8 SS Low Head Socket Cap Screw M3 Size, 10 mm Length, .5 mm Pitch (25 pack)http://www.mcmaster.com/nav/en...

g33zer on Oct 10, 2012 said:

Printed beautifully and a little cleanup made it look great. The McMaster parts are a perfect fit. Starting some tests now and I expect good results.

LiquidBeef on Oct 29, 2012 said:

Happy with the upgrade?

latigerlilly on Oct 7, 2012 said:

OMG! I went back and forth with MBI for 2 weeks and could not get my Replicator to print. I hesitated printing this out because the guy at MBI said that he won't be responsible if this causes my bot to break. Finally, I said, "heck with it, I'm gonna try this," and... it works! Yay!

The problem is that the delrin plungers will fail sooner or later. This is great. Thanks!

latigerlilly on Oct 8, 2012 said:

 Ugh. Spoke too soon. This fixed one of my extruders, but the other one is still kaput.... What the heck could be wrong with it?!

CrazyJaw on Sep 27, 2012 said:

This mod is so awesome it's almost sexual.

heathzap on Sep 23, 2012 said:

This mod has saved me. After multiple posts on Makerbot Support about crappy extrusions, dropouts, prints that fail after 30% etc etc I decided to make this mk8 replacement part. Wow...it has made a huge difference to my prints and so far no problems.

BIG thanks to emmett!

shawngrant on Sep 19, 2012 said:

Best Replicator mod so far!  A piece that had failed printing several times using some inferior ABS worked as soon as I made the mod.  Makerbot needs to take a design cue from emmett and whosawhatsis on this one and incorporate it into the Replicator.

Austin on Sep 10, 2012 said:

Thank you for the shopping list! Looking for the parts was actually a considerable hurdle for me, but being able to trade money for time makes it well worth it for me to make the extruders less prone to jamming.

brucethehoon on Aug 27, 2012 said:

Brilliant work! The only change I think I'll make will be adding some structure down below to guide the filament into the heating chamber. That said, once I fed it in, it worked better than the stock extruder for sure.


drandolph on Aug 25, 2012 said:

I built mine and here is my parts list. All sourced from mcmaster.com

1 #9657K331 Steel Compression Springs(12pack)
2 #7804K128 Hi-precision Ss Ball Bearng
1 #92855A310 M3 Size, 10 Mm Length (25 pack)

I love the function and the look!

LiquidBeef on Oct 13, 2012 said:

Thanks for the links, drandolph! 

AdanA on Aug 11, 2012 said:

Seems to work great, thanks!

The spring I had was from a Home Depot variety pack, and differed from yours: 0.35"-ish diameter, 0.98"-ish length, 0.04"-ish wire diameter. I drilled open the recesses slightly and all was well.

laird on Aug 28, 2012 said:

These are amazing. I printed a set, and they work beautifully. It's very easy to take filament out and swap filament, as long as you do it while it's still hot. Last night I managed to print to (almost) the end of a spool and then paused and swapped in a new spool and resumed, something that I couldn't do previously.

That's the same one I ended up using. The spring didn't quite fit into the hole, but it appears to be staying in place anyway. :-)

One thing that struck me is that while the springs are staying, they feel precarious, like they might pop out

emmett on Aug 11, 2012 said:

Nice job, that was fast.