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I want to build a mini CNC machine and need some lead screws. I was wondering I can simply 3D print some. There are a few 3D models out there but I want to know if printing it in PLA+ has enough strength for a small CNC. Is it possible?

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Expanding on some previous comments which are probably enough to warrant an answer:

What Trish said is completely right. Leadscrews are readily available parts and any dimensional errors in the leadscrews will be reflected in the output of your CNC machine unless you have some sort of compensation for them. Moreover, if the material is not highly rigid, the dimensions are subject to change over time, so any compensation would have to be ongoing manual adjustment or closed-loop rather than a one-time calibration. "PLA+" is an especially bad choice because it usually means PLA that's been modified with additives to make it less brittle, deforming under stress instead of holding its shape until it breaks catastrophically. CNC Kitchen's video on PLA+ elaborates on this.

With that said, if you don't need a high level of precision, or if you're in a situation where you're unable to obtain manufactured components, I think 3D printed leadscrews would work ok if you print them in the XY plane rather than along the Z axis. While nozzle width and discrete layers produce a sort of "stairstep" quantization of printed threads in the Z direction, that doesn't happen with the threads in the XY plane; the nozzle width limits feature resolution (oscillations per unit length) but the positioning of the threads is quantized only to the X and Y (micro)step size, which is typically on the order of 10 microns. Moreover, the strength and rigidity of the part printed in this direction can be very high, due to the offset-layered zigzag structure.

Back to accuracy of the part, though, it's important to note that whatever flaws your printer might have in XY positioning accuracy will be reflected in the resulting leadscrew. This includes non-linear effects such as belt paths being slightly trapezoidal instead of having perfectly colinear points of attachment to the carriage. In general, when manufacturing parts that will affect the accuracy of the resulting machine, you want to use processes that amplify the precision your tooling was manufactured with rather than processes that reproduce or amplify its flaws.

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Is it possible? Yes. Is it advisable? No

Lead screws need to be smooth and have little to no stretch and there can be a lot of tension on them. However, 3D prints are quite rough by the way they are made and super weak on tension forces - and not have a good compression withstanding either.

a 3D printed leadscrew is therefore not adviseable, especially since ready-made leadscrews and fitting nuts are cheap in the shape of nuts and threaded rods for the crudest setup.

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  • $\begingroup$ Moreover, the OP's suggestion of "PLA+" would be worse than normal PLA, since the additives make the PLA less rigid. This is a good thing if you're worried about brittleness, but a very bad thing if you want stability of dimensional accuracy. $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Mar 21, 2021 at 22:23
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    $\begingroup$ With that said, if you don't need a high level of precision, I think 3D printed lead screws would work if you print them in the XY plane rather than along the Z axis. Once you get to 8-10 mm diameter, threaded rods printed in this orientation are surprisingly strong. $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Mar 21, 2021 at 22:26
  • $\begingroup$ @R..GitHubSTOPHELPINGICE then you still have the issue of steps and roughness, unless you build a composite part from several prints. $\endgroup$
    – Trish
    Mar 22, 2021 at 9:46

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