MPSM V2 Improved Extruder (WK9)

by wileykyoto Jan 14, 2018
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Why limit this to the model 2? The model 1 OEM version was exactly the same. Only, the latest Pro versions look like they incorporate some of the features here and may even be better suited than the original OEM for flexible filament. This is my 3rd Pro printer. The first one the Z axis would not move. The second one I really liked until it started crashing the nozzle into the print bed. My hats off to Monoprice, they replaced each within 2 weeks. The latest one has the improved extruder on it, but the paper on the bed does not have the Monoprice logo. Doing its first print right now, the dang cat again. My model ones have had problems, but with consumables like hot end throats and nozzles.

Thank you so much for this! I printed this for my Select Mini Pro (v3) today as the tube connector broke on me last night (I secured the tube using Mr. Grip Stripped Screw Hole Repair Kit to be able to print). I'm just waiting for Amazon to deliver the PC4-M6.

I was able to get the bearing in with the listed screw. However, I just bought an m6 nut from my local hardware store and it doesn't fit. Anyone know what the exact dimensions of the nut are?

I don't have the exact part number, but I found out the hard way that there are three thicknesses of small nuts like these.
Standard, which you get if not otherwise specified, thin, and thick.
I had to buy a bunch of thin nuts for my 3d printing parts needs, since everyone seems to design with their size in mind.

Can anyone help me I tried replacing my v2 extruder with this and the stepper motor fell in. it seems the extruder is what holds it in place and I cant put it back together( the screws arnt in the right place when i pull it up to reconnect it).can I remove the face plate to the tower ? cant find any vids on taking it apart.

nvm found a solution by holding printer on its side i could use my hand to hold the motor from the z axis clearance long enough to get a screw in.

I bought a metal extruder mk8 to replace the plastic one after the fitting for the bowden tube got pushed out (the new cheapo version one), but it was 2mm to low and I wanted to keep the stock extruder bearing, so I printed your spacer (using a printed adapter for holding things together) and it works like a charm, thanks a lot!

If you have a Mini Delta, the bad news is the extruder gear has only 1 screw so Monoprice drilled the motor's shaft to be sure it won't move. I needed to move it up but I can't. So I will sand the WK9_Extruder_Base to align the "exit" with the gear.

More important, thank you for that improved extruder. I use it on my Select Mini V2. I added a small PTFE tube after the gear to reduce more the gaps and I can print TPU (95A) and TPE (90A) without issues.

How did you get the bearing out of the old arm? I'm having trouble with that. I also just made an inset version so you don't need the spacer and the gear aligns.

Can you post a link to the filament guide to the left of the extruder? Thanks!

Ooops - sorry I misread and thought this was a comment on one of my things - but anyhow, here's my make of something at least similar. Looks like the one in the photo is slightly different but pretty close.

Monoprice MP Select Mini Filament Guide
Monoprice MP Select Mini Filament Guide
by cmh

Hey, printed the cap, arm and base for my Mini V2, and noticed that I lacked the long screws necessary for mounting the base. My Mini has an aluminium frame holding the PC4-M6 connector with a nut, and the bearing seems to be unable to fit an M4 (can fit an M3), while the bushing goes right through the hole on the arm. I read below that there are multiple versions of the extruder for a Mini V2, and this might not be compatible. Any idea how I should proceed?

Attached pic of extruder for reference.

Yeah, you have the original extruder (that one that originally came on the V1). So if you do want to replace it, try this one. It should be compatible with your hardware.
Baseplate: https://www.thingiverse.com/thing:2029972
Arm: https://www.thingiverse.com/thing:2030554

MPSM Extruder Baseplate v1
MPSM Extruder Arm v1

Any advice for getting this to work with the smaller diameter MK8 gear? I believe it should give a little better torque, but of course the holes don't line up exactly and the bearing doesn't press down in the right location. I'm debating whether a bigger bearing would be enough to get this to work.

As you've found, this was designed for the geometry of the stock extruder gear. It's a complete redesign to make an MK8 version, it's not just the arm, the alignment of the feed path changes through the baseplate too. I would suggest looking for a printable MK8 extruder instead.

What is the point of the bowden fitting with the extruder arm? It seems more complicated to install and I don't understand the advantages it may provide.

It was an alternate requested by another commenter. The reason for it is if you're using a dry-box to keep your filament dry even when it's connected to the printer, you would run it through a bowden tube from the dry-box to the extruder arm. I don't bother, because I change the filament frequently, so it's never out of the dry-box for more than a day. But PETG can be particularly susceptible to moisture, so even a day, left out in a humid climate, can affect the quality of your prints.

I feel silly for printing the bowden extruder arm now... I assumed it would help feed the filament in straighter. Can I use it regardless of whether or not I am using a dry box? I'm hoping it works fine with the stock filament holder.

Yeah it should be fine, I would recommend just using a short piece of bowden tube ~10cm this will help guide it in with minimal friction and shouldn't affect your spool holder.

I'm confused, where does the bearing cap go? Is it visible in any of the real-world pictures (printed in yellow)?

Yes it's picture, it fits into the mating cuttout in the arm where the bearing goes, and helps hold the bearing in place, hence bearing cap. In the pictures you can barely make out the seam between the arm and the cap because it's a tight fit. But the screw that holds the bearing in place, first goes through the cap, then the bearing, then the arm.

ahh I hadn't seen that there was a bearing in the stock arm. I re-read your instructions and got it together.

I'm on the MP Delta, so ostensibly I need the spacer to make up for the notch in the stepper motor, but .. I was unable to loosen the nut on the extruder gear, so I modified the main base to put an inset on it so I could keep the existing extruder distance. I'll share when I finish.

Great, glad you got it to work.

M5-4 air connection also works. Currently using it.

Cool, good to know! Thanks.

Printed and installed extruder and my first print came in with a lot of under extrusion. I'm not sure if I installed the bearing correct or do I need to make adjustments to Cura?

From the pic it looks about right. But it's possible your model came with a different size bearing than mine. Can you check the inner and outer diameter of your bearing? This design is based on a 4mm ID and 11mm OD, if your bearing is a different size it may not be engaging properly. Alternatively it could be that your bearing is not free spinning. Check that with the bearing installed it's able to move freely, if it's not you may need washers on either side of the bearing.

That'll work. For future reference the bearing dimension is listed in the description. "Bearing (4x11x4)"

Did you ever come up with a solution? I'm dealing with constant underextrusion/jams since building this, and I believe the source of the problem is that the bearing is not able to move freely. I may try putting the old arm back on. Maybe we need to try one of the alternate cap sizes?

If the bearing isn't able to move freely try putting washers on either side of the bearing. Alternatively as mentioned in reply to the top comment, check that your bearing is the right size. This is based on a 4mm ID and 11mm OD bearing.

Same issue here - with under-extruding on an Aug 2018 V2.

It seems like the arm just won't stay horizontal, there's always a little bit of a "pop-up" visible on the far end from the spring tension. It seems like this is causing the bearing to be at an odd angle, which works for a bit then wears down the filament so it can't get a grip on it. If I keep pushing down on the end so it stays horizontal it works more reliably - but I'm not doing that for 4 hours :)

I verified the bearing is the same size as you mentioned and that it moves freely. I tried tighter / looser, washer / no washer, and tighter fitting caps, all the same issue. I ended up going back to the stock arm and that seems to work fine. It was the bowden clip that I needed to replace anyway so that works, but I hoper there's a way around it because I like your arm design better. Overall thanks for a nice replacement though!

Oh okay, that gives us a hint. Does your stock arm have the metal bushing that the screw goes through and are you using it in the 3d printed arm? If not, that's the problem. The bushing sizes the hole in the arm to match the m3 screw.

My MPSM V2 came with a much smaller bushing. It is 4.10mm in diameter and the hole in the WK9 arm is 5.22mm.

After writing this I found the solution, or at least almost the solution. The bushing still doesn't fit but it's much closer, I may just have to chamfer the hole. https://www.thingiverse.com/thing:2848474

Monoprice Mini Extruder Arm

Glad you found a solution. Unfortunately they like to change the parts that come on their printers without making it a new version. Also I don't have one of these so I can't properly model the different version. I do have some questions that might help me make a version:

1) Does the smaller bushing go all the way through the arm, if not how deep does it go?

2) Is the screw long enough that the head is above the bushing or shorter and down inside of?

3) Is 4.1mm the OD of the bushing, ps did you measure with calipers?

4) Did your stock extruder come with the same size bearing? (width 4mm, OD 11mm, ID 4mm)


I'll have to see if I have anything small enough lying around. For now, the stock arm seems to be working. I had tried the stock bearing and also bought some to try.

I printed this for my PrimaCreator P120 v3 as a replacement. The original "new type"extruder/feeder had a Bowden connector in which the metal ring broke so the Bowden cable came loose. Luckily I already had this replacement printed and it works perfectly. I used the M3 bolts, spring and bearing from the old part and added a standard PC4-M6 Bowden connector.

Awesome! Glad it worked for you!

I made this about as soon as I got my mini V2 because I heard the stock one was prone to breaking, only to find that mine seems to be a bit different (it already uses the PC4-M6 fitting attached to a metal flange). I do prefer this design though, as the metal flange that holds the PC4-M6 fitting bends quite a bit, causing some issues with over/under-extruding. My problem, however, is that I don't have long enough bolts to attach this as is and was wondering if you could upload a version of the base with countersunk holes? I could probably drill them a bit but I'm worried about structural integrity.

There's two different versions of the Extruder that come on V2's, sounds like you have the one that was originally on the V1. Which I suspect they've reverted to after how much trouble they had with the newer one. This replacement is not for the one you have, that's why the screews aren't long enough. But there are other differences, for instance I don't think the one you have uses a metal bushing in the arm, without which the hole in the arm will be too big. Also, I could be wrong, but I think the version you have uses a different size bearing. Which will effect the geometry and engagement of the drive gear.

The extruder you want is this one:
Baseplate: https://www.thingiverse.com/thing:2029972
Arm: https://www.thingiverse.com/thing:2030554

MPSM Extruder Baseplate v1
MPSM Extruder Arm v1

Unfortunately it appears that they've gone to a third kind as mine is different than both the V1s and V2s. Mine uses the shorter bolts of the v1, but the base on that model is too thick, and things don't line up right.
I'm not sure which arm is a better fit yet yet since I don't want to break the original until I have at least a working baseplate.
Would it be possible for you to post the cad file so that I can modify it to fit mine?

For the arm, you could try this one that another user modified already. https://www.thingiverse.com/thing:2848474

I could consider modifying the baseplate for the shorter screws. Can you do me a favour and measure the length of the screws, (not including the head) and the diameter of the head of the screw?

Monoprice Mini Extruder Arm

That arm looks good. I'll give it a try.

The stock bolts are 8mm. I had some 16mm bolts on hand but they're still not quite long enough to fit through your model.

Another thing I noticed while trying to fit your extruder is that the hole for the spring is about half a mm too small for my stock spring

Thanks for the details, I'll see if I can get together a variant for the baseplate. I'm looking into an arm variant too. Do you have a pair of calipers to accurately measure the diameter of the spring?

Thanks. That looks like it should fit better. I'll try that after work.
I will say I do like that your version has extended arms to make it easier to load.

I don't know why I didn't think to ask directly, but could you make a quick mod? On the Monoprice Mini Delta, it uses the same extruder, but the motor sticks out a little more through the frame. I got it to work by hacking some plastic out, but if you make a 23mm diameter by 2mm thick cutout around the gear hole on the bottom, it'll fit perfectly on the MPMD. Will probably need supports for that one section, but much easier to remove those than a chunk of solid plastic...

I really don't like supports. As an alternative, I made a motor spacer, that can go under the baseplate. A word of caution though, this will affect the alignment of the extruder gear. Though it's possible that because you motor stuck out farther, the extruder gear was also sticking out farther. Either way you should check out the allignment of the extruder gear with the filament path to make sure they're lined up. The extruder gear is press fit unto the motor shaft and can be slid in or out to allign it.

How did you get the old bearing out? Mine had moulded plastic in the center of it. Ended up breaking it out, and still can't remove the plastic from the center to get the screw threw.

I don't remember mine being difficult to get out, I think i just pushed it out with a small screw driver.

To print this I ended up with an emergency bowdenectomy. I used two spade terminals (ones with holes not lugs) not sure of the gauge but they were yellow. I opened one up slightly and slid it down the outside of the tube giving enough tube length to reinsert the end of the tube into the broken connector. I then gently crimped it, just enough to grab the tube. The second spade went under the extruder screw closest to the tube, One zip tie to connect the two spades and I was able to print the new extruder.

Thats would make MacGyver proud. Nice work, glad you got it sorted.

Thanks for this ! this save me a lot of job, and it's awsome. I made a video on my youtube channel (french speaking channel...). I made one in Polycarbonate, it works at the 1st shot !


Very nice design, well made, you rock !
Thank you !!

Thank you! And great video, I subscrubed.

First and foremost, thank you for this 1st class, professionally designed extruder!,,I realize this is probably an odd request, but is it possible to create a version with the arm that has another bowden tube connector? All of this rage about dry boxes, I thought a bowden connector on the arm would facilitate a more "environmentally controlled" path from dry box to the extruder. Also not sure if the extruder arm can be deigned to handle the connector and stresses.

Thanks for the praise!

And that's a great suggestion! I've added the new Arm version (WK9_Extruder_Arm_Bowden.stl). It's untested so can you let me know if it works? Should have plenty of strength to handle the load, but I am worried the M6 nut might stick out of the bottom of the Arm and drag on the Base. Depends on the exact radius in the nut edges, also may be low enough friction it won't matter compared to PLA on PLA.

Thanks for this. Got me up and running in no time.

Thank you for this mod. One question: When I installed it the extruder motor no longer has enough grip on the filament to feed it properly. When I put the old one back on it works fine. Is this a spring issue or did I possibly over tighten the mounting screws? My next idea is to use the improved extruder bottom plate with the stock arm. Thanks in advance for your help!

Stock arm on the improved bottom plate worked! Still wondering what I did wrong with the new arm though.

It's possible somethings different with your version, perhaps it's a different size bearing. Check that the bearing is 4mm inside diameter and 11mm outside diameter. If it's smaller, like a 3x10mm, there won't be enough tension with the arm I provided. That being said, if your arm is still working, you might as well keep using it. The main issue with the stock extruder is the bowden tube fitting, so replacing the base only fixes that issue.

Made sure to keep the new arm in my spare parts storage so I can figure it out later if necessary. Thanks again for the awesome mod! It's been working great since I got the arm figured out. Been printing all day :)

I love this thing! This is how the extruder SHOULD have been designed to begin with! But...does anyone else have problems getting filament in to begin with? I always find I have run the filament as far as it'll go, take the fitting off, finish snaking it through, then I can screw the fitting back on. Not a huge issue, just a bit aggravating.

Thanks! I think what you're missing is a small piece of bowden tube to guide the filament into the fitting right after the drive wheel. This small piece can be inserted into the hole where the filament goes.

That did it! Thanks!

You're welcome! The reason I designed it like that is that the small piece of bowden tube is needed for printing flexibles like TPU.

So is the installation just like the video in the V1 Improved Extruder were he cuts a piece off the original bowden tube and cuts that shape into a wedge?

Thanks again for this! I printed this a few weeks ago to have it on hand. Tonight my original cheap fitting broke and it only took about 15 minutes to swap out this replacement and get back in business. Your work is appreciated!

Welcome, glad it helped! And thanks!

Why is the hole for the arm bushing so over-sized? I'm surprised that nobody has mentioned this. Is this intentional? Can you provide a parametric solid file so that I can fix this for my own use? Thank you.

It was oversized so that standard shrinkage of PLA comes out at the right size. Unfortunately I can't provide a parametric file, this was designed in fusion 360. Is it possible you're using a different material or have a slightly different version of the printer with a different bushing?

It could be that mine is a newer version. This looks like it was designed to use a M4 screw for the bearing. I needed a M3. I reversed engineered it in Solid works. Now, it works great! I really like the design. Thank you for making it. I'm new to this website, but I can probably figure out how to post my remix of anybody needs it.

Yeah that's probably something, my version is definitely a 4mm inner diameter bearing. I only got mine in November and it was the newest one at that point. Is yours newer than that? Glad you got it modded to work for you.

I think I bought mine in December. Your extruder had already been designed. It was one if the first things I printed, but I only got around to installing it about two weeks ago.

Can you post the mod you made to the arm? Thanks

Thank you sir

Cool, thanks for posting it. Based on your screws it looks like your extruder is the original version, same as was on the V1. This arm will also work https://www.thingiverse.com/thing:2030554

MPSM Extruder Arm v1

I might be able to post a different version, can you meassure your bearing dimensions? Inner Diameter, Outer Diameter, and Width? I'll see about making a modified version.

I was able to use this part on my MP Mini Delta as they use they come with the same (poor) extruder from the factory. Thank you for the robust design

You're very welcome! Great to know it works for the Delta too!

Comments deleted.

Just back from the hardware store to snag a 6M nut, and it turns out it's too thick to fit in the slot.

Any Mcguyver ideas? Or perhaps where I might find a 6M nut to print?

I'd like to get this rig up and running again before making yet another trip.

The best solution is buying a steel M6 nut, but if you can't get out to the hardware store immediately, I'm attaching an M6 nut which is from a McMaster-Carr 3D model. I've printed it and it's a tight fit on the brass fitting, and wicked tight in the slot on this design, but it's a way to print threads for this design without having to deal with them being oriented the wrong way. Print the nut flat on your print bed with the smallest layer height that is practical (I used 0.04375mm with excellent results but I'm sure 0.0875 would work fine as well) and you'll have a nut that should work. It might require some sanding after the fact, or just sink it 0.1mm into the build plate in your slicer.

Is it just a little too big? It should be quite snug (if it's a standard 5ish mm thick nut it should snap right in). If it's close you could try carving a bit of a chamfer arround the openning. But if it's way too thick, something like a nylock nut, you would probably sacrafise the structural integrity of the extruder trying to gouge out enough space for it.

As for a nut to print, you won't be able to accurately print a 1.0mm thread. You might be able to find something that's just a friction fit, (self taping kinda thing)

I've found that with a small enough layer height, an M6x1 thread isn't bad IF the axis of the thread is perpendicular to your layers, which wouldn't be the case here.

I've included an M6x1 thread in my replacement for the new non-standard stock piece and it threads in quite nicely - almost acts as a locking thread. I've also found that a hole of about 5.7-5.8mm results in a good interface for threading in an M6 screw and works when the axis is parallel to the layers. Still, the steel nut as an insert will be far, far more durable.

I really like this design and think I'm going to print it out - my design is more of a band-aid for the crappy original part.

Monoprice Select Mini extruder cap to replace new OEM design
by cmh

I made this and notice a lot of clicking after installing it. I think the spring tension was too high so I drilled a hole in the arms and ran a bolt to reduce the tension on the motor. Premade holes would be a nice improvement

This was designed with the same dimensions as the stock extruder, so the the spring should be applying the same amount of tension. If you're experiencing something different it's possible you've got a stiffer/longer spring than the one I designed this for. That being said I'm not clear on where you're suggesting these premade holes should be.

Could be clogging too, I thought I had cleaned it out but I've been getting bad clogs the last few runs (before my stock bed wiring broke). I put the bolt through the narrow part of where the two arms are.

Oh yeah, clogging will do that. could be your printer runs a little cold, so the hotend is struggling to keep the filament melted as it's pushed through. I think if I were to add a tensioning bolt I would probably redesign the whole thing to better accommodate it. I'm also not a fan of how these extruder types twist the screw used as a pivot. Someday there'll be a better version.

Looks good, do you have any issues printing flexible filament? We have stock V2 feeder and it pushes filament up out of feeder. Have printed older parts for v1 to use but haven't replaced yet.

I haven't tried flexible filaments yet, but I designed this to work with them. As mentioned in the description, you'll need a short length of 4mm PTFE tubing, for the feeder gear to feed the flexible filament directly into the PTFE tube.

I am trying this to see if PETG works a little better by reducing slop in the system. Worst case it won't hurt.