mk7 ball bearing extruder drive

by jag, published

mk7 ball bearing extruder drive by jag Nov 19, 2011

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mk7 ball bearing extruder drive by jag is licensed under the Public Domain license.

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The mk7 is a marvel of simplicity but I'm still partial to ball bearing idler extruders.
I just don't love having that delrin plunger dragging on the filament and I like to be able to quickly release the tension so that you can pull the filament out and replace it easily without having to run the stepper.


6/26/12 - I just uploaded a new experimental version with a recess for a nut for the tensioner. I haven't printed it as I'm out of town at the moment but feel free to give it a try. It's called mk7-lever-drive-tension-nut.stl (It should be the last file). The lever is unchanged.

Either print out the parts separately or print out one of the plates (with or without the quick release).

Remove the support from the lever (where the bearing goes, it's just two thin walled cylinders)
Remove the support from the underside of the body.
Remove the support from the quick release (two cylinders again)

If you have a 3mm tap, you might as well run it through the holes for the tensioner and the bearing.

Install a 623 (or R2) bearing (3mmx10mmx4mm) in the arm with an 3mm x 10mm countersunk screw
Put the pin for the quick release in the quick release and install the screw (3mm x 20mm)
Snap the lever onto the drive and install the tensioner screw or quick release.

Install the drive the same way you would the normal mk7 block. Tighten the tensioner screw until the stepper misses steps when you hold onto the filament (as opposed to just slipping).

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is there any way to make this work with a 608 bearing, the kind that skateboards use?

Not really,  a 608 bearing is half the width of the stepper so, it would need to be a much bigger assembly.  The mark 5/6 filament feeders could be tweaked for a 608 but they use a different hot end.

Just made this and I love it! Got the bearing from amazon and here's the link if anybody would like.


Its prime eligible so that means 2 day free shipping for whoever has prime!

I would suggest an improvement -- I have already stripped the threads in the plastic because it is plastic (duh). A better solution would be to put a recess for a nut on the inside of the drive plate for the tensioner. Then we could add a 3mm nut (glue it in) and not have to worry about the plastic stripping out. By the way, I tried just putting a nut on the inside, but there is not really room.

Second, I attemptyed to put a spring in between the release lever and the tensioner. I found some 3mm "fender washeers" but even they were too small -- they slipped inside the slot in the arm and then when I took it apart again, the arm was split in two. I may try a larger washer after I print it

So I am back to the stock configuration right now. I do not have the program to modify the plate for a nut, so I may not try again.

I finally got around to doing this modification. I haven't tested it yet though. I'm not in the same state as my printer so I can't print it out.

Here's a video of it in action using sdp-si spur gear S10T05M020S0505 in place of the MBI special part. There's some flex on the tensioner (it's using a spring so the spring is overpowering the ABS). I am going to modify this design to have no overhang on that side (for dual extrusion) so I'm not too worried about that part:


Also works with a 77R2 bearing (available at Ace Hardware) which is 1/8" bore, 3/8" OD and 5/32" wide, or 3.175mm x 3.97mm x 9.525mm compared to a 623 3x4x10.

The bearing screw is M3x10 (remember flathead screws count the head).

This is a very clever print! I think it may need some more room behind the tension bolt in my application but other than that it's almost perfect.

I've since learned that the size is just "R2", not sure what the 77 prefix means. I ordered a second one from McMaster (for about $6.25) and I'll post the McMaster p/n if it works out.

Thanks! I never got around to measuring that screw, I just put one in and then cut it off to length with a abrasive disc. I'll update the instructions.

What size are the other countersunk screws? Source for them?

Do you mean the little one for the bearing? I would guess that one was 12 or 14 mm. I thought they were 8mm and ordered some from mcmaster carr but the I didn't realize that for the countersunk screws, you measure the length from the top of the countersink, not just the length of the screw. I ended up using one that I had left over form my aluminum build platform since I only used 3 of them to hold the platform. I just shortened it with my dremel tool. I'll try to remember to post the actual length of that screw when I get a chance (or I could look in the cad files). You could probably also use a 6-32 or 5-40 screw from your local hardware store.


I'm just waiting on my bearing to show up in the mail... My MK7 isnt working very well with various filaments - just doesn't want to get a good grip and feed. Hoping this is just what the doctor ordered.

My copy is installed and in use right now. Not bad. I'm fighting some issues with filament that's a bit shall we say 'loosely toleranced' and from time to time, it's too small and stops feeding. It would be really cool if there was a mod to allow for a spring to be placed somwhere to act as a tensioner, to keep the ball bearing pushing against the filament.... just in case anybody is bored (It's beyond my skill level)...

You could easily put a spring between the quick release and the arm though if you are using a spring, you may not need a quick release since you may be able to release it by squeezing the spring. In that case, you could just use a spring, a screw and a washer.

This is great stuff and I will be attempting to print my copy. I was wondering what others have used for Object infill (%), Number of shells and Feedrate? My Base Profile is set to SF35-Thingomatic-HBP-MK7 with the extruder temp at 230C and HBP at 110C.

Any info/recommendations are appreciated!

I think I printed mine at around 50% infill. I'm not sure what the extra shells setting was. If it's anything other than 0 you will probably have a little open space in the arm where the hole for the bearing is. It doesn't really matter though.

You could probably just print it with the base profile and up the infill a bit. My extruder is at 220c and my HBP is at 110.

I love my new filament drive! It would get in the way of dual extrusion, but I'm not planning on that for the foreseeable future.

A great addition to it would be a filament dust remover. Just four thin walls surrounding the input hole, where one would put two pieces of sponge to keep dust away from the filament drive...

I made a untested mod for your extruder to make it compatible with the ultimakers bowden system...

Instead of using a skateboard bearing, I'm thinking of using one of these: http://www.thingiverse.com/thing:4640http://www.thingiverse.com/thi...

Bearing for filament spindle
by chylld

Good luck with that. I don't think there is anyway to print one small enough to work. :-P

It looks like its designed so you can do filament changes, unlike the stock mk7 (see http://www.thingiverse.com/thing:13727#jsid-1321936628-209http://www.thingiverse.com/thi... )

Can anyone confirm?

mk7 ball bearing extruder drive
by jag

It is. I've found that you can chase one color down after another and it works about 2/3 of the time. What works better is to pause the print, release the quick release and pull the filament out and shove a new filament in.

Pausing isn't a viable option. It has to work as well as my hack of placing the heater barrel very close to the pulley. If you provide a "chute" that's just as effective, then it might work.

I haven't looked into where it's hanging up. If it's hanging up after the drive and before the heater barrel, it could maybe be fixed by screwing the heater barrel up until it's touching the plastic (I actually had a version with a protrusion and a 6mm hole to screw the heater barrel into but there wasn't really enough room for it. I could put the 6mm hole back in but there isn't zoo much plastic there for that. I think what tends to happen is that if there is any curve in the plastic, it just follows the drive wheel and shoots out the side. There isn't a chamfer on the hole for the filament after the drive wheel but there also isn't much room for one and I'm not sure how much of a difference it would make.

The additional advantage of my hack is that you gain ~4
–5mm in Z as well. I think you could still design a bearing-based idler with this in mind.

I think I'm going to tweak this to use a standard skateboard wheel bearing.

Also, what is the difference between the mk7_drive_plate.stl and the mk7_drive_plate_qr.stl???

The bearing is ~22mm in diameter and ~7mm in depth. The center hole is the perfect size for a nylon spacer.

I was thinking about pulling the stl files into OpenSCAD, Blender, or Sketchup. I'll decide which one once I decide how things need to be tweaked. Anyway, see the photos below. It is a "Lucky Hardball (Reds)" bearing.

the qr one includes the quick release parts

what are the dimensions of a standard skateboard bearing?

If you mean 608 bearings, it's going to take a bit of work to fit them in there...

I like the drive and I like the fact that you provided the Alibre part files. I was able to download then and make an assemble to better understand the drive. Dave

I could have uploaded an assembly but I got tired of uploading files...

Great design again! In regard to uploading files I have found the easiest way to save a whole assembly in alibre is to "save all as", then point it to a folder you wish to upload. Zip the folder. Then upload the whole folder. The best part is that all the assembly constraints are also maintained. :)

I'll have to remember that trick.

I've found that sending assembly files is tricky. You have to make sure that you include all of the part files with correct paths or folks have trouble opening the assembly.

I've uploaded updated files along with the alibre files.

There are now STLs for plates either with or without a quick release.

This looks really good, I'll need to make one I think. Keep us posted on printing results and heat effects.

That's my main concern now that the heat is so much closer to the stepper than it was on the MK6.

Regarding the dual extrusion-mirror the drive concept. The mirrored one would place the bearing on the "other side" of the motor pully, but coulldn't a clever person make the extruder motor turn the "other way" ? The current motor goes clockwise for foward and ccw for reverse. Isn't the "sense" of the extruder motor a motherboard parameter? It could easily be done in the wireing, of course.

It just occurred to me that this design may not work for dualstrusion, would that be accurate?

you should be able to mirror the parts and print a left and a right for dual extruders.

The problem with using this with dual extrusion is that the idler needs to be on the inside side (the side that is right up against the other extruder) which means there's no room for a spring loaded bearing like this, which is a shame...

It could be redesigned so that the tensioning mechanism was above the stepper. It would take a little figuring so that it didn't interfere with the filament path but it's probably doable. I'd have to do away with the snap in pivot for the arm though.

Oops, good point.

Knew you wouldn't be able leave that alone!

Yeah, it was just a matter of time. It was almost ready when I saw you the other night. It just needed a little more tweaking.

I'd like to see a quick-release like the MK6 one.

Just printed it... Just what I needed because, nice as the Mk7 is, getting a replacement delrin plunger or stuff like that would be a rather difficult task here in the latin american backwoods.

I just can't quite figure out how the quick release parts fit in!

Did you cut the support out? Once you cut the two supporting cylinders out, you can shove the pin through and then put a screw in the pin and tighten the screw through the idler arm.

I'm working on it...

I have mk7 and thinking the same thing... I don't like the plunger.

I will give this a try when I get the bearing!

Let me know if you need some help testing it out...especially if you can solve the color-change problem.

Awesome! Awesome! Awesome! Cheering for you! If you do upgrades please link them to this page so I don't miss any :P. Whoohooo! this is great! Thanks!

Glad you like it. I'll be posting any revisions to this thing. I'd only create a new thing if there was a reason to have a separate one. I'll be sure to post comments when I update anything.