Prusa i3 lead screw upgrade

by harari, published

Prusa i3 lead screw upgrade by harari Nov 18, 2015
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After a year with my printer, the standard threaded rods started to get annoying. I decided to upgrade my printer with proper lead screws.
I couldn't find a set that I was sure would fit my printer, so I made one myself. Now you don't have to.

This set fits the standard Prusa i3 with 8mm straight rods, 8mm lead screws and Nema 17 motors.

update #1 :
included .skp files for further customization

update #2 :
modified the right X axis carriage to include a recess for the rim of the lead screw nut.

update #3 :
fixed manifold problems with X carriage parts.

More information and photos can be found here:

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Printer Brand:



Prusa i3










printed with pla.

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Hi , great work i am going to upgrade my prusa i3 too . Actually is a matter of days but i have 3 quick questions that i would like to make.
First of all , what kind of bearings did you use. I mean where can i buy them!
Secondly, have you seen great improvement considering the printing quality?
Latest but not least ! What exactly did you changed in the Marlin configuration ?

Thanks, glad you like it.
I already covered all of that in my blog post on this. Please follow the link in the Thing Details to find it. (there's also a comment on the post with links to all the materials I bought for this)

If you still have questions after reading, I'll be happy to help.

Good luck!

Hi again, ! I make all the parts !! As i can see you should put some more width in the holes of Xaxis pieces where we connect the nuts with M3 screws. It's only 1 mm ! i can sent you photos if you like !
I would like to help me , if you are willing of course , with the steps/mm configuration. I have Nema 17 with 1.8deg/step.
The rods are of 2mm pitch but they have 4 starts so the lead is 8mm. With a microstepping of 1\16 what is the right steps/mm??
I made tests with 2560steps/mm (prusa calculator) , 1600 and 400 ! none works !
Thank you in advance

anyone else finding alot of flex in the z motor mounts?
any tips, or just print beefier ones?

Mine are pretty stiff with regular PLA.
What are your settings? What material are you using?

im using pla with 35% infill and 3 shells
all the other parts are nice and thick/stiff, but the motor mounts are thin and unsuported(ones i had in last had a "support rib" going up to the back) when i run the axis i can see the motor move and the mount bend
what settings did you use?

your settings seem fine, I printed them at 40% with 0.2mm layer height and 2 shells.
maybe your material is a little softer than mine..
you could try thickening the top part, that should help.

Two questions:
How did you remove the bearings from the brackets they are in? The ones I picked up are in the same set up.
And what are the size of the knurled nuts you used? I gathered they are M3 and 4mm in outer diameter? I measured the holes in the X-axis carriage parts. It's the length that I'm unsure of. The area that they go in is 8mm in height, so did you go with 8 mm or shorter?

Thank you.

found the solution. just have to rotate the bearing so it will slide out. Needed to use a spare 8mm rod for leverage.

The solution was just a few scrolls down, but glad to hear you got it.
the knurl nuts I used are 5mm OD, M3 thread and 5mm height. I print the hole for them a bit smaller than the OD, ~4.5mm + print shrinkage.
The hole doesn't have a step or anything, it's just a hole all the way through. I make sure to insert the nuts on the opposite side of the print so it actually grabs as you tighten the screw and not just bottoms out.

What exact frame are you using? I'm having difficulty getting these onto my plywood box frame with any accuracy so I figured it was time to get something more appropriate. I don't want any compatibility issues with these parts, so I want to know which frame type you designed these around. Thanks in advance!

well, i bought it more than 3 years ago so the original listing is not available. It is made of dibond aluminum, that's a sandwich of aluminum-plastic-aluminum and I don't see a lot of those around any more.
anyway, I think the holes are standard prusa i3.

Ok thanks!

Comments deleted.

Hello, i want to print these parts, could you tell me what's the distance between axis ( rods and smooth axis ). Thank You.

hello do you know or not what's the distance between axis rods and smooth axis please?

Hello, i still don't know, but i had designed my own top and bottom, with 8mm smooth axis, 22mm distance between smooth axis and lead screw, to match Styx i3 8mm x 2mm Lead Screw Z Axis Option design

ok thanks
very nice

Dec 28, 2016 - Modified Dec 28, 2016
harari - in reply to omega776

Hi, sorry for the late response. I was away for a while.
I just measured the distance between centers of my 8mm straight rod and 8mm lead screw. It came out 21mm.

good luck!

Missed out by 1mm :))) . Thank you for response.

Do I have to modify the firmware once I apply these rods?

yes, you need to remeasure the steps per mm value. there's an explanation in the link to the project in the thing details.

good luck.

Did you have to drill out the Z motor couplers to get the lead screws to fit?

No, you can buy 8mm couplers.

FYI, your XAxisNoMotor stl is still the one without the nut recess as of 8/7/2016

thanks! I'll take care of that ASAP.

Made some modifications including adding the nut recess, widening the smooth rod holes, removing the upper leadscrew bearing (for those of us who don't believe they're needed much), adding strain relief for the smooth rod and beefing up the motor and shaft mounts to fit 42mm high motors while still using my original screw holes in the frame.


i3 8mm Leadscrew upgrade Z Axis motor mounts for 42mm high motors

very nice. good work.

Does anyone know the distance between the threaded rod and the smooth rod on the z-axis portion of this?

The ZaxisNoMotor part the lead screw hole is 1mm in diameter smaller.

Hi Harari,

How do you tension de x belt?
Great design

Belt tensioner

Nice one! well done!

Unfortunately, this wouldn't work on my printer as the belt passes through a thin channel. I intend to revisit this project and make adjustable tensioners in the carriages.

look at this one: http://www.thingiverse.com/thing:1474991 you could use that one for tension the x belt.

Styx i3 (Updated)

Hi Harari,

Do you think if it's good or no for bearing LMUU12 ?

I guess you mean LM12UU..
LM12UU are 12mm inner diameter and the ones I used are 8mm. the outer diameter would be different too so they would not fit.
You could edit the files ad make it fit, though.

Will this work on the makerfarm prusa i3v?

The i3v has square aluminium extrusions instead of round stainless steel rods. These would not fit.

when you upgraded from rods to leadscrew, did you change any programming in marlin? i ask because the pitch on the threaded rod does not look the same withthe thread on the leads screw and i assume it would change how big or small the steps are?

Yes, of course. There's a link in the thing details with detailed explanation for why and how I did everything. Check it out, there's instructions for how to recalibrate your printer.

Thanks for sharing this!

It seems like the XaxisNoMotor's inner hole's diameter for the nut/lead screw is different than the one with the motor (8 instead of 10.5). Wouldn't fit for me (8mm lead screw and 8mm rim don't play nice together without force/scraping)
Is that something you can fix (and maybe add the recess as well ?:)

Prusa i3 lead screw upgrade - improved XaxisNoMotor
by natiz

very nice!
I'll check my files too.

How could I take pk08 apart?

The bearing needs to rotate 90 degrees on its axis inside the frame (the axis that's perpendicular to the surface on which it's sitting), this can be done by leveraging with a pen or a rod (some force needed), then it needs to rotate 90 degrees on the other axis to meet the two notches on the one side. the bearing can then slip out through the notches.

good luck!

That works! Thank you very much.

Made it, works great on Prusa i3 single wall frame. Thx

Trying to find a parts list for this build.

What type of bearings are those that hold the top of the lead screws?

Also, very nice design. I've worn our 6 threaded rods already and anxious to get this upgrade done.

I think the bearings are called KP08.
if you have a different type of bearing, you can modify the model to make them fit.

good luck!

How did you go about securing the smooth rods in the parts? I noticed they're open ended. Cheers

Friction. The holes are just big enough for the rods to fit. You could use some loctite for extra grip if you'd like, but I found this design sufficient.
Another idea would be to add grub screws to secure the rods. You can do this yourself with the .skp files I uploaded, I'm not sure i'll have the time to do it myself.

Feb 12, 2016 - Modified Feb 12, 2016
LukeTansell - in reply to harari

Thanks. I got impatient and built my own, and I'm doing a couple of grub screws. I love the texture and look of the blue you used though!

I can't really guarantee because the brackets seem quite different.
The X carriage brackets on both sides seem similar, but you'll have to check the distance between the rods to be sure.
The motor mounts and top brackets are clearly different and I can't see the screws or holes in the frame so I can't determine whether or not they'll fit. They might.
You can modify the files to make the holes fit your frame of drill new holes in your frame to fit the parts.

I am printing these at the moment, may i ask you what the ideal distance is between the 2 leadscrews?
Thanks for the upload

the distance is dictated by your motor mounts and top brackets. the rods need to be parallel to each other, so the distance will stay the same throughout. you just need to make sure the carriage slides smoothly and without interruptions or friction.

Thx for the reply, i realize that, is it possible when you have time to measure the distance on your printer? thx

I just measured the distance between the lead screws and it came out 32.3cm. note that that's the distance BETWEEN the lead screws and NOT center-to-center.

I hope that was helpful.

Yes, I can measure that for you, but it'll take some time (next week).

I have tried to print these twice now and both times the holes for mounting the brash nut are not complete there's a bit of material missing from the outside so it's like a u but almost joining if that makes any sense

i think I understand what you're describing, but that cannot be something with the files. I printed these several times and I know of more who did the same and it came out fine. My guess is that it has something to do with your printer, either the filament, calibration, slicing settings or environment cause the loop to not close and leave a gap on the top.
Does this happen during the rest of the print or is it confined to the top layer?
it should not affect the structural integrity and strength of the piece, there are 4 holes and that's more than enough to hold the nut. there is not much force applied to that part in that direction.

Im going to try and reslice them tonight and try a print again. just found it kind of strange, one thing i did notice is im getting a warning when bringing the parts into Repetier it says....the object is not manifold. This essentially means thats its not watertight. the could cause problems during slicing. This could be my problem i just don't know how to fix that or why im getting that

Siplify3d and Slic3r didn't throw any exception at me, but after another careful inspection I found the problem. It seems that the model was fine but something went wrong in the conversion to .stl
The file was re-uploaded, please try it now.

sorry for the late response, I was REALLY busy lately..

Hmm.. interesting. I don't recall getting that message myself. I'll check the files again.

I like your design and would like to make a few changes (add a precision Z-axis endstop holder, Prusa Hephestos style X-tension, remove bracket for X-axis endstop). May I have the original (non-stl) files for this?

Comments deleted.

I'll upload the .skp files in the next two days.

Hello Harari! I would like to modify these for use with the HIC Prusa i3 kit I bought. Any way I could get the source files to remix?

I'll upload the .skp files in the next two days.

Hi, great job !
Do you experience wooble with both ends of the leadscrew being constrained ?
I took the opposite road - see my thing 1147671 - but I'd love to try yours. Can you please confirm the specs are those I have put in my thing (I don't see how to attach something to comments!)

What are the dimensions and specifications of the lead screws?

8mm diameter, 300mm length.

Are these derived from the original prusa i3 models? If so do you have the openscad source? I was preparing to do something similar for the Wilson 1.0 and it would help a lot if I just had to tweak the z parts a bit to mount on am extrusion.

I didn't have the original files and I couldn't find models that I was sure would fit my machine, so I had to remodel everything from scratch.
The design is very similar to the original with some modifications to make room for the lead screws and bearings.
If you want, I have my .skp files (sketchup).


A sketchup file isn't useful for me (running GNU/Linux and I've never been able to get it to run under WINE), but I still think you should upload it! There are far too few parts for Prusa derivatives that have corresponding CAD files and it might be useful for someone else.

just uploaded the files.
there must be a way to convert the files to something you can work with.
I'll see if there's a way to export CAD from sketchup.

Errr. Uhhh.

  • Your prints are awesome!
  • How does one make a bolt, especially one so nice looking? I have a tap. I'll go read your site, but it didn't look like
    there was a lot of discussion on how to make the screw!
  • WHY don't we print awesome PLA screws? Maybe one an two inches in diameter with the highest threadcount one can print?
    I guess very, very skinny screws are better (at resolution). Why not print 15 screws and put them as planets in a planetary set?
  • Is resistance with the original bolt bad or good? Doesn't this old bolt reduce ringing/resonance with movement?
    As jerk is applied, the rolling resistance keeps the whiplash down. A perfectly smooth action would transmit
    the bouncing perfectly though the system. (Of course, I don't see bounce there.)

Dumb questions. I didn't get to take physical mechanisms in college...

Nov 20, 2015 - Modified Nov 20, 2015
harari - in reply to gddeen

Well, first of all, glad you enjoyed it.

The lead screws themselves were not self-made, I bought them off eBay. I don't have the tools for that kind of job.

I don't think plastic screws will take the loads, especially printed ones. Moreover, they are longer than any axis of the print area so you would have to print them on a larger printer or print in pieces and glue perfectly to keep the contour continuous.
A printed screw would also have tiny lines all over it, as every other thing printed in this technology. This would introduce more resistance and an imperfect print would cause even more problems to the point of uselessness.

I don't think the lead screws add (or subtract less) vibrations. There are another pair of fixed stainless steel rods that help keep everything sturdy. The old threaded rods were of softer metal and were not fixed on one end. Not only that I doubt they dampened any vibrations, they could have resonated and amplified some vibrations (this was especially apparent as they started to squeak and ring when homing, caused by the friction between the screw and nut).

The unsmooth surface of the threaded rods caused only larger degradation over a shorter period of time. The smooth surfaces and harder material of the lead screws and nuts would slow down the wear dramatically.