Prusa i3 MK2 Clone Extruder for 8/12/18 mm sensors and MK8 Hobbed Pulley

by geoffsim, published

Prusa i3 MK2 Clone Extruder for 8/12/18 mm sensors and MK8 Hobbed Pulley by geoffsim Apr 20, 2017
4 Share
Download All Files

Thing Apps Enabled

Order This Printed View All Apps



A part of these Groups

View All

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

Thing Statistics

15697Views 2457Downloads Found in 3D Printer Extruders


Modified Prusa MK2 extruder parts to fit 8, 12 and 18mm sensors, and the MK8 hobbed pulley.

12 July 2017: 12 and 18mm sensor mountings have been modified to provide more space for the sensor cable routing.

I have included the modified scad files, as required by the GPL license.
Note that these files may require additional files, which can be found in the Prusa GIT repository.

If you like my work, please consider a small donation (a dollar or so) to support my other projects.

Print Settings

Printer Brand:






Doesn't Matter






Whilst waiting for my genuine Prusa i3 MK2 to arrive, and having been spurred on by Tom Sanladerer's Cheap i3 MK2 Clone videos, I went ahead and built my own 24V version of a Prusa i3 MK2 Clone using the STLs freely available on Prusa's GIT repository; a 6mm Aluminium frame; TR8x8 Z axis screws; a Hictop 3mm Aluminium heated bed; a 360W 24V PSU; and a genuine E3Dv6.

However, it became clear (and pointed out by Tom in a summary video) that the common MK8 extruder did not fit well onto the current design. I took to modifying the SCAD files to fix this issue, and a few others, and this is the result.


  1. Move hot-end 1mm right to accommodate the MK8 7mm effective diameter.
  2. Increase sensor fixing to hold the more common 12mm and 18mm sensors.
  3. Allow the sensor cable loop to fit without interference.

The 8mm sensor is approximately 21.5mm right and 9mm back from the nozzle.
The 12mm sensor is approximately 27mm right and 7mm back from the nozzle.
The 18mm sensor is approximately 32mm right and 3mm back from the nozzle.

Print in ABS 0.4mm nozzle; 0.2mm height; 2 shells; 3 layers top and bottom; 25% infill.

As I wanted a look-alike clone, I also modified the PSU cover to take a 24V 360W PSU, and the RAMBO cover to take a RAMPS 1.4/Arduino combo. These are posted seperately.
The last two pictures shows the completed clone and some sample printed parts. Running TMC2100 stepper drivers on the X and Y axes has made my machine almost silent!

More from 3D Printer Extruders

view more

All Apps

Auto-magically prepare your 3D models for 3D printing. A cloud based 3D models Preparing and Healing solution for 3D Printing, MakePrintable provides features for model repairing, wall thickness...

App Info Launch App

Kiri:Moto is an integrated cloud-based slicer and tool-path generator for 3D Printing, CAM / CNC and Laser cutting. *** 3D printing mode provides model slicing and GCode output using built-in...

App Info Launch App
KiriMoto Thing App

With 3D Slash, you can edit 3d models like a stonecutter. A unique interface: as fun as a building game! The perfect tool for non-designers and children to create in 3D.

App Info Launch App

Print through a distributed network of 3D printing enthusiasts from across the US, at a fraction of the cost of the competitors. We want to change the world for the better through technology, an...

App Info Launch App

Quickly Scale, Mirror or Cut your 3D Models

App Info Launch App

Treatstock is an online platform that offers decentralized manufacturing services such as 3D printing and CNC machining for clients all over the world. We offer free and instant access to comparati...

App Info Launch App

3D print your favourite design with NinjaPrototype, a professional 3D manufacture with consistent quality and speed.

App Info Launch App

Hi - I'm new to 3D printing, and have a question about this design:
Is there a reason not to use PLA when printing this? Can't stand up to the temperatures?

You answered your own question there :-)
PLA starts to soften at around 35-50 degrees.

If you don't want to use ABS, try PETG, although watch you don't weld the parts to the bed (lean the bed with window cleaner to stop it sticking too much).

HI Geoff,
Any chance of MK3 Clone extruder for 18mm sensors and hobbed pulley?

I made the 12mm MK2 for myself, and am happy with it. I made the others just for completeness.
I may have a look at the MK3 some time, but not for a while.
You can always have a go yourself!

Thanks for this, what nuts/bolts are needed?

The same as what is required on the real printer.
Have a look at the Prusa online manuals for the details.

Any chance you would be willing to modify the 18mm sensor MK8 for use with a Bowden setup?

Quick answer, no.
I made these changes for the two clones I built. I have no plans to make any more changes.
You could have a go yourself...

"MK8 12MM" extruder cover on bottom side of photo. Could there be some error in dimensions?

Nope. By design. Allows insertion of hot end.

Is there a .3mm v6 version of this by any chance?

Hi Geoff,

Thanks for sharing this (and your other mods). It appears that even the 8mm version may position the probe too close (2-3mm) to the body of the part. The wire doesn't have enough clearance to pass between the probe and the body. Am I missing something?


I didn't move the 8mm version. It is the same as the stock part, apart from the MK8 modification.
I intend to update the parts to use a single screw to affix the sensor at some stage. I will increase the distance of the probe on the 8mm version at this time, too. Or you can do it yourself as the scad files are provided (look at soff and cabinc in extruder-main.scad).

How far are you on doing that?

Do what? I have decided not to do the single-screw fixing mod as I am happy with the 12mm version - that's what I use on my clones.
As far as the spacing for the probe wire for the 8mm version, you can do that yourself - I have pointed to you the changes in the scad file.

well, ive brought the part up to the latest singe screw version and modified the cable guide

Perhaps you can post on Thingiverse as a remix?

Prusa i3 MK2 Clone Extruder for 8/12/18 mm sensors and MK8 Hobbed Pulley 1 Screw better cable loop edition
by MaxRink

Hi Geoff,

Followed your suggestion and reworked the original Mk2 body. Filament holes are 1mm to the right & 8mm sensor mount is 2.5mm to the right. Thanks for the inspiration.


Prusa I3 Mk2 Dolly Extruder
by Cr3470r

nice work! I have a question! When I printed the body and the cover I noticed they have a different diameter is this ok?!!!

Yes, it's by design. If they were the same, it would be difficult to fit together with the e3d in place.

thanks you again for your time!

Very nice. This "thing" saved my butt. I ordered an E3D hobbed pulley from Filastruder and the filament path was too tight with the original MK2 extruder housing. This one worked perfectly. Can someone tell me what size screws and nuts are needed for securing the pinda probe? I had the old style before.

M3 square nuts and 12mm bolts.

Comments deleted.

Great updates, thanks! With the MK8 hob gear, won't the e-steps need to be updated to accommodate this different size?

Updated from what? However, the short answer is yes. It's important to tune your extruder on every new build, anyway.

There are also 10mm inductive probes (mentioned with 10mm detection distance on ebay, not sure about that detection distance but i would try).
Could you also make extruder for 10mm probe? =)

You sure it's a 10mm diameter probe? I have never seen one.

It is unlikely that an 8mm sensor has a 10mm detection range, especially when sensing aluminium. My tests showed about 2mm for an 8mm sensor, 3-4mm for a 12mm sensor, and 6-8mm for an 18mm sensor. Capacitive sensors have a better range, but are more sensitive to temperature. If you have bought this one, let us know what sort of range you get from it.

Doh.. It is not inductive sensor it is actually hall effect, does only detect magnetic field.
Test results with magnets and ruler: 8x1mm magnet ~5mm, 8x4mm magnet ~9mm.
Can be used if magnets are glued under heatbed. Maybe original Prusa MK2 use hall effect sensor and magnets inside heatbed for XY aligning?

No, no magnets. Prusa PINDA is a custom inductive sensor. The sensor senses simple copper circles on the top of the bed. A standard 12mm inductive sensor with a 4mm range detects a 3mm aluminium heat bed at around 2mm. The 18mm device is about 4mm.

Hi! Thank you very much for these! What do you use as the idler shaft?

I just used a 5mm bolt, cut to size.

Thank you for making these, exactly what I've been looking for! Just a question regarding the 18mm: Did you incorporate the changes that you mentioned in the summary regarding the sensor holder? Thanks!

Yes I did.
The main picture has not been updated yet.
However, the part has been updated, and the actual picture of the part show the change.

Thank you for making these, they would come in handy - unfortunately, the extruder body for the 12mm sensor is missing most of the screw holes. Could you upload a repaired version? Thanks!

Just testing you ;-)

Hi Geoff,

Can you tell me what are the bearing you used to work with your mk8?
It's look like yours is bigger than the original?
Am i wrong?

I assume you mean the idler bearing. This is a standard 625 as per the Prusa instruction manual.

Hi Geoff,

I have build my clone using Tom's guide as well. I am going to print your part and change things out.
But I have another issue that you might have a solution to - I also used TR8x8, but the brass nuts don't fit into the original Prusa parts - what did you do to fix this?

Print a shim or collar to make the brass nuts a snug fit; cut out the piece of brass between each of the holes and the outer edge of the nut; place the nut in the shim, and the shim into the prusa part. The bolts will then fit. You can use washers, but I found I didn't need them.

Can you post the ship or collar you used to make the brass nuts a snug fit? can you take pictures of the modifications you made with the T8 brass nut?

ah - yes, that makes sense.. Thank you for swift reply :)

Prusa i3 MK2 Clone Brass TR8 Nut Adapter

You can also print these if your in a pinch :)


Trapezoidal Nut for Prusa i3 MK2
by Mach0gr

Thanks :)
My china E3DV6 clone is printing like SH**. So I am currently waiting for an original set. It will arrive Monday. I hope that I can obtain decent PETG prints with this build and an original hot end.

As you can see in the last photo, I used those at first. I replaced them with the brass ones a few days later, once I had worked out how to fit them.

I am working on an 18mm sensor version, and will post it here when done.

can you post please the psu cover??and what are the dimensions??

I am working on this at the moment. I will post it when done.

Can you post the SCAD files?


NIce work! What type of bearing did you use for the x axis idler? Thank you in advance.

I used a 16 tooth idler timing belt pulley with dual bearing.

The Original one uses 20 (without tooth) idler timing belt pulley and on the stepper motor the 16 tooth one

I am also using 16 tooth idler timing belt pulley with dual bearing but it is smaller than the original one. Did you modify the x carriage to align the belt. One more question, what's the part number of the heat bed that you used? Can't find one with connector on the side..

I only noticed that when my genuine prusa arrived.
I may swap out the idler with bigger ones - when I find them...

I need one for the 18mm probe. :)

Working on it.

My SCAD changes don't work well for 18mm probes. I optimised the changes for 12mm only.
If I get enough requests, I will see what I can do.

For now, get a 12mm probe. It works quite well, albeit only 4mm sense range (about 2mm with an aluminium plate).

You don't perhaps have one with for the M8 Probe? Or maybe the Openscad files?
Great job on the clone. I'm waiting for a few parts to arrive then I'm going to build one too.

That was quick thanks!