Mk8 upgrade without cutting for REP 2

by infinityplusplus, published

Mk8 upgrade without cutting for REP 2 by infinityplusplus Nov 26, 2012
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I really did not want to cut the plastic on the top of the replicator2 extruder. So I made this derivative of the mk8 minimalistic.


I have added 2 front version 3 files. The back piece is still on version 2. The first version 3 front piece has had the bearing slot opened up to allow up to a 10mm diameter bearing inside, and I have tested a 10mm bearing, works great. I have also put 2 cutouts in, the one on the back side to help with friction interference, and the one on the top to eliminate hitting the cover when no filament was in the printer, depending on your bearing size.

The second file I have also remove a bit of material from the front where the bearing contacts the drive, to accommodate an 8mm bearing, untested. Anyone who tries the different bearing sizes let me know if this helps or not.

Download the version 2 or 3 files. Print at 100 percent infill. I printed at .25 layer height.

Seems to be working great now and it has made my prints so much better than the stock plunger.

I have gotten all the holes to line up correctly now in version 2 and there is very little after print work. Cut out the bearing slot support, Install your bearing(I used a longer set screw). Bolt on as shown in the picture. Install your spring and put your printer all back together. Be careful not to over tighten the screw in the top left corner, it needs to take out the slack but too tight can cause it to bind and not allow the spring to do its job. Very similar to what you see in previous extruder mods, except you don't need to cut the plastic on a REP2 with this one.

I am still looking into an easier way to make the bearing support post, it is a bit hard to remove but nothing a small utility knife couldn't handle.

I used:
3x9x4 or 3x10x4 bearing . the 3x8x4 bearing front piece has not been tested by me.
one flat head m3 x 10 .5 bolt for the back right side
Re purposed the original bolt for the left side
m3 x 10 .5 set screw for bearing
1-3/8 by 23/64 spring from a cheap spring assortment I bought. Here is the link to the assortment I got my spring from. The spring tension is touchy because of the compact nature reducing leverage. This spring from this kit has worked great for me as long as your pieces are not binding and moving freely.

I have heard concern over the back piece having issues with heat at the base because of the PLA. I have not seen any warping or failure and I put it through the ringer.

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I am going to see if this can be made to fit the replicator 1. I am having problems with printing on a rep1 and I believe this is the solution.
Thanks for all your hard work on this.

Let me know if you end up working on the Rep1 version, we're looking to do something simliar. We might modify the latest from @whpthomas (http://www.thingiverse.com/thing:42250)http://www.thingiverse.com/thi... in order to fit the Rep1 and have the added benefits of this thing.

Replicator 2 Extruder Upgrade

This fix has been a tremendous blessing. If you're wondering whether or not this is necessary, don't. Immediately print one of these, or some variation, because you won't get more than 5 or so hours of prints without the filament slipping. My experience was one of great frustration with both filament slipping and having the PLA stick to the baseplate, painters tape, or Kapton. This fix solves the root cause. Now, as a result of the material properly and consistently extruding, the PLA sticking issue is also resolved. I get good bonding to the painters tape, decent bonding to Kapton. I used a roller bearing (McMaster Carr 7804K128), an M3x10 flat head screw for the top right location, and an Ace Hardware steel spring (wish I had the specs, it was .032" wire, about 10 winds, inner diameter was just a touch too small to fit on the hexagon cone, so a little dremeling was necessary). At any rate, I have had about 20 hours of printing with gray and white without a single PLA feed issue. Thanks infinityplusplus

I am going to try and make this from Delrin at work. I just hope I can import the solidworks files to autocad. My plunger is bad that I cannot print it, and Makerbot is always out.

This is FANTATSTIC! I think my spring is a bit beefier than yours, since it was harder to fit into the backPiece... but nonetheless, it has stopped my feed issues!!

This modification made a huge difference on my machine's performance, before I couldn't print at less than 0.25mm layer heights, now I'm printing at 0.1 with no problem! (I had to modify it slightly to accept a different machine screw)

Works great for me! I couldn't find a set screw or bearings, so I used 4 washers and a cap screw from the other direction, and it seems to be working well while I wait for the screw and bearing I ordered to show up.

Hi Infinityplusplus, just to check, should I use back_piece_ver2.STL with front_piece_ver3.STL? Which bearing should I use with ver3? Thanks!

Yes, you should use the version 2 back piece with whatever front piece you need for your application. If you have a 9mm or 10mm(623) bearing, use the file labeled front piece ver3. If you want to try a 8mm (693) bearing use the front piece labeled with 8mm. I would personally try for a 9mm or 10mm bearing, it will give you better compression on the spring and help clear the cover on top when no filament is in. Good luck!

I want to add this mod to my Rep2 - no luck finding the parts locally (hardware, hobby, RC shops). Can anyone shed some light (or share some links) to the parts needed online. (I'm in the US) Thank you for a great mod.

See my post above- links to all the parts and hints for the screws. Cheers!

this is the bearing I used, Ebay was the only place besides hobby shops that didn't sell them in packs of ten


I have not tested the version 3 arm with different bearings but I opened up the tolerance so an eight or ten mm bearing should work. They seem to be easier to find.

Mcmastercarr has the 8 and 10mm bearings along with some springs and the screw needed.

Thank you - this works really well for me too. I saw that Back Piece ver2. has a hex depression which takes a M3 nut. A short piece of M3 studding together with two M3 nuts and a washer is used to adjust the tension of my spring. It does need to be fairly stiff. I did not have a bearing to hand, (Christmas!), so used a spare cog wheel instead. Care taken to ensure parts were smooth and i greased the inner faces with lubricant.

I like the tension adjuster. That should be helpful to anyone with spring tension issues.

I ordered the parts and will be attempting shortly. Thanks!

I'm running this mod right now! I found that the suggested spring didnt provide enough force, and the filament wasnt coming out as fast as the roller demanded, so I added the long smaller diamater spring from the Harbor Freight spring pack inside the larger spring. My test object seems to be printing ok. I also used a 4x9x4 bearing since I didnt have one at my local hobby shop. I just drilled the hole out to 4mm and used a 4mm set screw. I'll report back once I test more!

Well, all 3 of my test prints failed due to too little material extruding. I'm going to put the stock plunger back on and print another one of these with thee 3mm hole, and get the correct bearing size. Maybe that'll help...

As long as your bearing is lining up and not being hindered I doubt it is the issue. You could try zenod's spring tension device, and make sure your top left bolt is not causing too much friction between the two pieces. I have heard some issues of people's drive gear slipping as well so you may want to check the set screw there.

I have not tried a smaller bearing, so i am not sure. It could always be changed a little to make it work, the hole for the bearing would just need moved forward a little, or you might run into clearance issues.

Hi there, it may be because all the springs I tried weren't stiff enough, but this didn't give me enough pressure against the extruder head and I ended up going back to the stock gizmo on the R2. After I watched this video (http://www.youtube.com/watch?v=QOJN_8AAC9U)http://www.youtube.com/watch?v..., I figured out I needed to crank on that thing WAAAAAY more than the R2 manual suggests, and now I'm back to normal.

Having said that, I really like this design and I am a little skeptical of the stock pressure plate, because it seems like it's just going to work itself over time.

I found and added a link to the spring assortment from where I got my spring from.It seems to be the biggest issue the mod has; finding a suitible spring. I am also going to work on a set that will not cause as much friction between the two pieces to help reduce after print work.

Thanks infinityplusplus, I appreciate that, and after posting about what I found in that video, I'm still having extruder jamming problems. I'm starting to wonder if it is my model or my filament, but I'm getting close to giving makerbot support a call.

I'm also ordering that set, thanks again!

Tried making this twice, I finally got it to work using parts from each of the two sets I've printed, but I still have some issues with it. I am trying to get the proper spring tension, prints great up to medium quality, but has some issues on high quality prints for me. An awesome mod, but needs a little tweaking to get it to work just right.

Just an update: I finally got around to touching up the pieces from this mod using a file and some sandpaper, and got the spring dialed in for proper tension. It now prints like a charm. I  performed my longest print to date with this thing, on high resolution at .2mm layer height no less, and it performed perfectly for a nearly 5-hour print! My Replicator 2 is now working better than it ever has.

If this mod gives you issues, don't get frustrated, just make sure clearances are good, and you have a stiff enough spring. Spend a little time tweaking it and cleaning it up and this puppy will work like a champ!

HI Infinity,  Any chance you could send me a copy of the solidworks files saved before 2010?  My gives me a "future version" error.  I was going to adjust the design slightly to suit my spring and bearing.  Cheers. 

Try the new parasolid files I have uploaded  Solidworks has terrible (as in none) backwards compatibility. Hopefully you can load the parasolid files and then feature recognition will pick up what you need. I don't have any experience with it though so let me know how it works, if it doesn't we will try something else.

Thanks mate, imported and featurised exactly as you predicted.  An amateur question I'm sure - what face do you align with the build plate for the 2 pieces for the best print?  I assume there are no auto generated supports required?  Cheers.   

Or could you tell me if the system ends up really tight because of the spring, or you can move the system easily.

It is firm feeling when I press down on the end. Perhaps someone who has a better resourced spring has a better idea. I just grabbed the one size bigger than what I was going to use for Emmets original, to make up for the small loss of leverage.

I am still having problems with my extrusion, but I suspect that the spring that I am using is too tight. Could you give me more detailed info of the spring? length, strength, compression value or else? 

Since the spring I used is a spring from a cheap assortment, I don't have detailed info on it. What I can tell you is that it is .032in  diameter spring steel, with the above measurements  being total length and diameter. 

This mod has fixed all my rep2 printing problems.

Couldn't get my Rep2 to print for more than a 1/2 hour before this mod, now I can print for hours without any problems.

Always nice to get good feedback. I am glad it is working well.

This might work on a Replicator (1) too. Do you have any trouble loading the filament? In mine I have to squeeze the springs when loading.

With the new version I was able to feed the filament in with the load procedure running. The first model did not have enough feed guide and the filament wanted to go all over the place. If i need to I can still get a hold of the side and squeeze. I can't comment for sureon the replicator (1) but as long as there is nothing that would interfere with the spring holder It should work.

Looks great!  Wish I had waited another week before modifying my R2!