Minimalistic Mk7 replacement

by whosawhatsis, published

Minimalistic Mk7 replacement by whosawhatsis Jan 10, 2012
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Minimalistic Mk7 replacement by whosawhatsis is licensed under the GNU - GPL license.

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This Mk7 replacement features a spring-tensioned, quick-release 623 bearing idler, and won't interfere with dualstrusion. The back is also open to make it easy to clean the teeth of the drive gear.

This works with MBI's Mk7 and QU-BD's MBE extruders. It will fit the Mk8 as well, but the Replicators have plates above the extruders that will interfere with the spring arm. There are several derivatives that solve this problem, most at the expense of the rear clean-out opening.

The best shaft for the bearing seems to be an M3x10mm flat-head screw, inserted from the motor side of the idler piece. A piece of 3mm filament should also work in a pinch.

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how am i supposed to get the bearing in the longer piece?


I've been using this design since the beginning of my story with 3d printing, although I chose it from many I couldn't really appreciate it until I had recently opportunity to try original Wade's solution.

Minimalistic Mk7 replacement saves you A LOT of time and nerves on inserting a filament! This is the fastest and cleanest solution! Only one thing I discovered is to have one spare arm because it cracks easily.

Thank you for shearing!

any hope for a wallace mK7 adapter mount?

The Wallace's X carriage requires a pretty long hot end. A Mk7 won't reach the platform unless the carriage is redesigned to mount the extruder much lower. You might be able to make that work by mounting the extruder sideways, but the Wallace is a pretty outdated design, and that effort is probably better used elsewhere.

Harbor Freight sells a spring assortment for $4.99. Harbor Freight item #67562. It contains some compression springs that are 9/32" x 3/4". Dimensionally, it seems ideal but I am not yet sure the wire gauge is heavy enough. I'm building a printer so I'll report back on how well this performs.

Maybe someone else has already tried this particular spring?

My first tests with this were with a similar assortment. The 23/64 X 1 3/8" spring should provide enough force, though you'll probably have to change the spring diameter value in the scad file and re-generate the STLs in order to accommodate it.

..thought I had 623 but they are 605..know of any that fit a 605z? I was looking at this one perhaps: http://www.thingiverse.com/thing:32315

Right and Left Minimalistic Mk8 replacement - Modded
Comments deleted.

There is a small support post that you should be able to pluck out with needle-nose pliers. Just crush it and it will come loose. If you need to do more than that, either you have serious print issues or you're trying to use the wrong bearing. A 623 should be 4mm wide with a 10mm outer diameter.

Comments deleted.

what size spring do i need

I'm still trying to find a spring online. Got some from Mscdirect and they're not working. Too long (so I cut one down) and not stiff enough. The filament slips at accelerated speeds, unless I apply a little pressure on the lever. So close! :) The shipping from Home Depot for the assorted pack is crazy and it's a 30 minute drive to go and get them. Has anyone found an online source with reasonable shipping? Or at least somewhere that will sell be spring plus other things I might need to make the shipping worthwhile?

How are you using it to put pressure on the gear without slipping? Is it some sort of bearing?

Yes, there's a 623 bearing in there.

I don't know if this was covered, But would the bearing and screws from the makerbot supplied filament feed thing be compatible with this?

Where can I find the bearing?

Yup, that's the one. I normally say don't pay more that $1 each before shipping, but since you can get free shipping on that one and you only need one, it's probably an ok price.

really nice design! curious what you are using for the filament driver and where to find it.

Could you please post the specs for the spring? (OD, compressed length, etc.)

Springs are a PITA to spec, which is why I designed this not to be picky about what spring is used. You want ~1/4" OD (up to about 10mm if you modify a variable in the scad file). I don't have a number for the compression strength, but it should be difficult to compress between your thumb and finger. Of course, a longer spring will be more compressed during normal operation, and thus does not need to be as stiff to begin with.

I use a spring from the $7 Harbor freight assortment. Works great. There are several springs of that size in that set. Bearings you can get from amazon cheap too.

This may be a dumb question, but how do you get the bearing in here?

I printed this thing, and there is a post running right through where the bearing should be, which looks like its for a screw, but there is no way for me to push the bearing in with the screw post there

That's a support that's meant to be removed after printing. I usually grab it with needle-nose pliers and pull it out.

I love this thing! The stock MK7 extruder constantly gave me problems. This one always works perfectly. My only complaint is when it's time to change the filament it's hard to feed in the new piece. This is the way I do it, but it's still a little tricky: First if there is already filament in the machine I cut it off close to the extruder inlet with a pair of diagonal cutters. Then I run the stepper until all of the filament has been drawn past the motor. Then I stop the stepper, push the lever and insert a small allen wrench (the same size as the filament) into the hole. I feel around until I find the top of the filament and push. I feel the resistance as I push it into the extruder and then the slight bump as it hits the entrance to the tube. I continue to push until it has bottomed-out inside the tube (this is important). Then I remove the allen wrench. I take the new filament and try to remove the curl and make it as straight as possible. I press the lever again and while holding it down (here comes the hard part) I try to find the entrance to the tube and push it in. I release the lever and run the stepper and hopefully stuff comes out!

It's easier if you pull the old filament out rather than trying to push the last piece through. As for difficulty lining up the new piece, I'm working on a new version that will fix this: https://plus.google.com/105535247347788377245/posts/8FCXgHdxrJwhttps://plus.google.com/105535...

Thanks Rich! Much appreciated!

Would anyone be willing to sell one of these? I really only need the plastic parts.

Hi, I'm trying to build an extruder and I am deciding if I choose this design or wade gear extruder design. What you recommend me? Why did you not recommend this design with a 3mm filament?

The Makerbot store doesn't seem to be listing its "High Torque NEMA 17" stepper any more.  From comments in http://www.thingiverse.com/thing:6300http://www.thingiverse.com/thi... I think it is the 17Y402S-LW4-01 from http://www.anaheimautomation.com/products/stepper/stepper-motor-item.php?sID=12&pt=i&tID=75&cID=19http://www.anaheimautomation.c... with 111 oz-in.

What motor specs do you need to drive 3mm or 1.75mm filament through this extruder?

MakerBot Stepstruder MK6

I do not recommend this design for 3mm filament. The increased back-pressure requires a lot more tension on the idler to prevent the filament from slipping, and I couldn't get it to work reliably.

I also don't recommend running 3mm filament with a direct-drive extruder, at least not with a drive gear as big as the one MBI uses. Even if the torque is sufficient, the resolution is marginal at best. Using the smaller-diameter Mini Hyena 8x5 drive gear has the same effect as increasing the gear ratio, and should provide sufficient resolution.

 Cool.  So, 1.75mm filament with a 10.56 dia MBI drive gear (per http://store.makerbot.com/mk7-drive-gear.html)http://store.makerbot.com/mk7-... works adequately with MBI's 111 oz-in Nema 17.  But a  Mini-Hyena- 8x5 with its ~ 6mm effective diameter may require proportionally less torque: 111 * (6/10.56) ~ 63 oz-in.

One could move a step down the Anaheim nema17 table to the 17Y302S-LW4 and probably be OK.  Or, with some adaptation for the gearbox, one could use any of the http://www.phidgets.com/products.php?category=23http://www.phidgets.com/produc... nema17 gearmotors and get a big torque and resolution upgrade.

Works great! I've mentioned it in my recent video: https://www.youtube.com/watch?v=Kcnh28rpS30&feature=plcphttps://www.youtube.com/watch?...

I also have another video on my channel showing it printing at 120mm/s

Great job! Works great. The suggestion about the spring from the home depot assortment pack works wonderful. Thank you.

Since the ABS is springy, and your lever is long, could you replace the spring with a bolt?

I tried, it doesn't work too well because the bearing doesn't allow kinks or bumps to pass easily and you end up with a jam half way through the print. Just get a pack of assorted springs off ebay.

At least one person is using it that way. You lose the quick-release functionality using it that way, because you can't compress a bolt by hand.


I made a replacement top for the replicator that makes it possible to use this minimalistic extruder replacement on a replicator with dual extrusion.

Here: http://www.thingiverse.com/thing:26679http://www.thingiverse.com/thi...

Replicator extruder top
by toreg

I'm at maker faire this weekend with springs for this to give away. Keep an eye out for me and say hi, or tweet @whosawhatsis and I'll let you know where to find me.

This makes me want a MK7 :)

I ended up putting a piece of 3mm filament (a little longer than the thickness of the arm) in to hold the bearing and used my soldering iron to melt it in place. :)

Very, very nice :)

(Shaved off a bit to make it fit 693 bearings.)

Very cool.

One unintended advantage of this is you can put tick marks on the bearing and watch the tick marks go by to make sure it's extruding correctly!

I've been drooling over this upgrade, however, I only had a 3x8x4mm Bearing on hand so I made some modifications Pictured below. I shaved the front part where the bearing is mounted. I purchased the "assorted spring kit" from the hardware store. Unfortunately for me there wasn't a compatible spring in my pack. I had to cut down one of the more powerful springs to make this thing work.

After getting it mounted on my bot I ran the most horrible filament I had on hand, a piece of filament I purchased from http://3DPrinterStuff.com3DPrinterStuff.com. This wonderful length of plastic ranged from 1.48mm to 1.85mm in the span of less than 1 meter. I'm happy to report I was able to print most of a calibratio
n cube with mostly no issues! Also you'll note from the pic that I changed colors midprint! That's a first for this guy.

this is awesome, now that I found a spring that works :)

US makers .. Homely Depot carries a $4 spring assortment, the magic spring is in there!

With the spring I used out of that pack, I printed the original STLs and then drilled the hexagon spring holes out to 12mm. Works great! :-D

I upgraded my MK7 motor with a higher-torque motor to be able to print PLA faster (which it now does), but I had to drill the hole in the feeder gear to 6mm and I didn't quite get it on center. The Makerbot plunger system didn't have enough range of motion to pick up the slight difference, especially on thinner (1.6ish mm) filament so it would feed for a bit when the gear was slightly closer to the plunger, and slip when it was slightly away from the plunger. I printed this replacement out, and even with it not feeding properly all the time, it was good enough to install and it worked lilke a champ. I printed another copy, now that it was feeding continuously, and it came out great. Thanks!

The only thing I have trouble printing now is the blue I got from http://3dprinterstuff.com3dprinterstuff.com. Most of their stuff is less than 1.75mm (as small as 1.5mm in spots!) and varies in diameter quite a bit from foot to foot. The standard MK7 can't print more than a few feet of it. This replacement design doesn't seem to mind the fliament not being completely uniform in diameter and I'm now able to print all of the other colors I bought from them, but their blue filament seems really soft (more flexible than it should be) and strips extrememly easily even with a stiff spring. I bought some Makerbot blue and that works great.

Glad it worked for you! Everyone and their third cousin twice removed has had trouble with the quality of 3dprinterstuff plastic. The white that I bought was too soft too. I got thought the roll with a lot of failed prints, but I won't be buying from them again.

That off-center bore in your drive gear is going to cause a bit of unevenness in your flow rate. If you start pushing for really high quality, you'll want to get a Mk5 drive gear, which has the right 6mm bore for that motor.

I've been thinking about mounting the Mk6 motor to one of these, but he
shaft is so long! How did it fit your extruder? Would you post some pics in the "I made one" section?

I posted a side view. If you look closely, you can see the shaft sticks about halfway into the fin section of the heatsink, but is nowhere near the fan. This upgrade has been great for printing some of my substandard (small) filament.

Thanks for the note on the Mk5 drive gear - I'll check that out. The 3dprinterstuff filament varies in diameter so much that the slightly offset drive gear is the lesser problem. It prints Makerbot filament just fine. I might also try making my own as I have access to a machine shop and it looks reasonably challanging for my skill level.

The motor I used is the high torque stepper from Makerbot. The web site says 5mm shaft, but the one I got was 6mm. I took a dremel to the hole in the center of the heatsink on my MK7 to allow the 6mm shaft through into the heatsink fin area. The fins in the center have already been removed so o
nly the hole needed work. The shaft doesn't extend far enough to interfere with the fan, so it's fine that the shaft is a bit longer. It just sticks out a little further into the heatsink fin area.

I did have to file a flat on the 6mm shaft to make the setscrew grip well. There was a flat on the
shaft, but it didn't go close enough to the motor body to pick up the Mk7 drive gear set screw. My trick there is to put silly putty around where the shaft meets the body of the motor to protect the bearings/bushings of the motor. Then I filed the flat I needed. When done, I removed the metal fi
lings as best I could and then pulled the silly putty off. You could see where the silly putty had trapped some of the metal filings, so it definitely helped. You could probably use a similar trick if you wanted to cut the shaft shorter with a hacksaw - just cut slowly so as not to heat the silly
putty up too much. I would grip the part I wanted to cut off in a vise to keep the shaft from turning while I was cutting.

I printed a copy of this extruder with my original "sometimes feeds and sometimes doesn't" extruder. By a series of rather fortunate mistakes, I accidentally had the shells s
et to 11 instead of the 1 I wanted, so I got 100% fill, which ended up being more like 50% fill because my extruder only printed half the time :). That version was installed to print the nicer version shown in the pictures (not intalled) as the brown one on the bearing bag. The ugly one still work
s so well, I haven't gotten around to dismantling/replacing it with the pretty one yet. When I get it all replaced (probably happning in the next few days), I'll definitely post a picture of it with the larger motor.

I found a spring for my extruder that I'm very pleased with, and I've ordered 250 of them. What I'm thinking of doing is selling a "kit" on ebay (buy it now) with one spring and one bearing for a few bucks. This should be all the additional hardware you need for the upgrade to the Mk7, and these parts will also be needed for my upcoming multi-configuration extruder design.

Do you have any updates on this? I'd love to buy a kit since I can't seem to find a suitable spring anywhere. Also having the spring and bearing in one kit would be great.

Yeah, I've developed the concept into a more universal extruder that's nearly ready to release, but it turns out that 3mm filament needs more tension, so I'm making some adjustments to increase it. Once that's tested and ready to release, I'll start selling the kits for use with both versions, and probably update this with the improved geometry I've come up with for the other version.

Any update on the kits ?

I'm ready to buy one... ;-)

Sorry, I've run into some snags. I want to make sure these things are rock-solid before I start selling them. I'm now finally dogfooding a version of this extruder, and I'm iterating the design of the idler to make sure that it is just right for this spring.

I'm interested in the kit parts, to make it easier to print and play with the design.

In particular, I want to tweak the design to fit under the 'beefier' bracket, http://www.thingiverse.com/thing:26880http://www.thingiverse.com/thi... that would be awesome. That bracket holds the feeder tubes very nicely, and I'd think that putting a 'twist' into the arm would let it fit under the bracket. Since it's an OpenSCAD
edsign, that makes it easy to tweak and test.

Beefed Up Replicator Extruder Bracket

I'll buy a kit as well.

nice man, I will be waiting for this !!

What parameter in the extruder.scad file can I change to increase the bearing opening from the 623 (10mm I think) to a 12.7mm diameter bearing? I found a 1/2" router bearing at ace hardware that looks like a good fit. It is a 12.7mm x 5mm size. I haven't quite figured out the scad program source yet.

There's no parameter for that. It's designed to be used with a 623 bearing, and I do not recommend trying to use other sizes, but if you search the text for "circle(6);", you can find the spot and try to modify it.

Any approx idea on the spring rating in pounds?

If no one has the spring rating than wire width would help.

Sorry, my notification for this post must have gotten lost.

Anywho, I've got a 5/16" diameter spring that's 1.125" long with a .032" wire width from an assortment that seems to work well. I'm currently sourcing springs for testing so that I can recommend (and possibly sell, along with the bearing) a spring that is known to work well.

It's too bad springs
don't have standard sizes the way bearings do.

This works great.

Thanks !! :)

Just posted mine, but haven't tried it out yet. I modified it a little to take a wider spring and to use the same bearing set from this thing: http://www.thingiverse.com/thing:15289http://www.thingiverse.com/thi... Had to print with support on, but my mod seemed to print ok.

Couldn't get the other one to exert enough pressure to keep the extruding constant. Hoping this one will do the trick since it allowed me to use a really strong spring.

MK7 filament guide spring loaded with ball bearing
by DieselG

Any chance of you posting your mod files?

I modified the files to use a spring up to 8mm (just changed a default parameter).

That bearing-in-a-bearing thing is just weird and inefficient.

Weird, yes, inefficient, well it was more efficient than going out to buy another kind of bearing.

I finally got it installed and it's working well so far.

That seems like the problem-solver for me! As I have plenty of filament with unfortunately less then 1,75mm thickness, I need more strength on the plastic in order to get the filament pushed through.

But I don't have a spring like this here, so it would be great if the design could be changed in a way that I would be able to put force on the handle bei screwing a bolt against it. Maybe I find some time to change your design into that direction...

But so far, thanks for the design! I'll definitely try it out!

So, just to unform you out there: the designed worked for me in the way that it perfectly fitted on my MK7. But unfortunately, there arosed another problem: my filament (very thin one, around 1.6mm) slipped in the gap between the idler and the drive gear, which stucked again. So I switched back to the original MK7 but removed the cooler plate so that the cooling air from the fan could cool down the place where the drive-gear and the filament meet each other. It seemed that this place was too hot which made my filament (unfortunately not a filament from makerbot, theirs is working like a charm) get too soft und stuck in the extruder.

So, as a conclusion: the decision works and maybe you can resolve the "slipping in the gap"-problem, too. I even managed to use the design without a spring - I just made a hole in the idler arm and screwed in a bolt, that I could use to put force on the arm (see pictures).

Maybe this helps other
people. But once again: great design that just fits perfectly!


Just curious, did your implementation of the extruder work without the spring and a ap screw in its place?

Seems that the job does not call for much in actual movement of the idler bearing, only force, and that the flex of the printer arm should be enough for the amount of compliance needed to take up .2 mm or so of filament variance.

I was working on a similar idea: http://www.thingiverse.com/thing:15759http://www.thingiverse.com/thi... but I have not yet done extensive testing of it (I am waiting for the 4mm fan).

Direct Drive extruder
by misan

I would like to ask for the spring.. which size of the spring is the best to use.

It would be also nice if the spring used can be easily purchased somewhere like on ebay or such.

The spring I'm using is actually a bit short, so it doesn't currently have as much tension as I would like. I'm going to modify it so that the spring is compressed a bit more and/or try other springs. There's already a variable for the spring diameter, so you can modify it for any spring that has the right force when compressed to the proper length.

I was so excited to print the STL file that afterwards I had to modify the ends of the spring to fit the hole which turned out pretty good but now it will be even better because I'm aware of the spring diameter variable in the SCAD file. Thank you! :)

brutally simple. love it!!

Oh man this is great and an scad file too. Great stuff as usual whosawhatsis!!!

Oh, very nice. I wonder if it could benefit from a hole at the top, as a filament guide, to keep it from derailing. Cool thing is, this doesn't seem like it would care if you're using 3mm or 1.75mm filament. I wonder if a 608 skate bearing could be substituted, thanks for including the SCAD files.

The filament goes through a hole in the lever. Along with the groove in the drive gear, this keeps the filament aligned. The picture shows it with 3mm filament, though that is not compatible with the Mk7 hot end. I plan to make a mounting that will allow it to be used with other hot ends that do work with 3mm filament.

A 608 bearing would be way too big to fit between dual extruders, and it would also be harder to find an 8mm shaft that would not stick out far enough to collide with the motor body.

Ah, right, now I see the hole in the lever. Beautiful in its simplicity, I'll try this on my MBI Stepstruder and see how it goes. It certainly looks like it will make switching from 1.75 to 3mm filament a LOT faster.

I really like this

This just made my head cave in at the shear simplicity. Great work!

looks pretty sweet, nice idea