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So I bought a prusa i3 kit from a company called folger tech off of ebay. I've built it and even printed out a few parts, but I noticed that a lot of noise seemed to be happening only while the x-axis motor was moving the extruder. Then I noticed if I put my finger lightly on the plastic part of the x-carriage I could dampen the vibrations and pretty much eliminate the noise I noticed. Then I took apart that part of the printer and examined everything and all I could notice that seemed to be loose was that nut that allows the z motor to push up the x carriage. I don't know if I got a bad nut, or a bad screw, or is it's just supposed to be this way? I thought it was kind of a weird way to build things with a screw turning a nut, because I thought that it would bind up. But now I'm wondering if that is why it was so loose fitting (to reduce friction)? So does it need to be that way? Or could I get a different nut? Or is there some better way to go about fixing this issue? Or perhaps it's not even an issue.. idk.

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    $\begingroup$ Could you send a picture? $\endgroup$
    – hroncok
    Mar 29, 2016 at 14:30

3 Answers 3

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It's probably intentional. Threaded rods are almost never perfectly straight. If the nut is rigidly coupled to the carriage, then the slightest deviation in the screw will either cause it to bind up or appear as artifacts (e.g. z-wobble) in the print. By making the nut slightly loose, it can move around a bit to compensate for wobble. See e.g. this design and this design for how this is commonly implemented in other printers.

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I agree with Tom about looseness.

I would suggest 2 solutions:

  1. Use grease which will reduce friction (and vibrations as a consequence);
  2. Use better clutch (coupling). Full aluminium couplings are prone to conduct noise (vibrations) from the threaded rod. You can use Oldham coupling with a plastic floating member. This will definitely reduce noise on Z axis.

Of course you are encouraged to use both solutions :)

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I do not agree with the answer of Tom.

In a proper design, the nut is supposed NOT to be loose, especially in the Z-direction. All options of the nut to move can cause imprecise layer heights and Z-wobble. There is also the possibility to introduce Z-wobble by bent rods and good contact of the nut. However, Z-wobble is not what I want to address.

Yes, to me, it seems possible that your rod or your nut (or both) are looser than they are supposed to be. However, I don't know the exact design of your printer. Usually there is some play along the axis, but hardly any perpendicular to it. Typically this can introduce a hysteresis (wikipedia link) in the placement of the X-carriage. There is a nifty design against this, which most likely should also help you to get rid of your noise: Thingverse: Z-axis anti backlash for Prusa i3.

First, however, you should check the following:

  • Are both your Z-axis drives set to the same height, or is just one of them doing the work (which would be very rare, by the nature of the design)?
  • Is your nut lose in the X-carriage? While the nut should not be lose itself, it should be totally fixed in the X-carriage (again: typically, but I don't know the FolgerTech approach).
  • Try other nuts from the hardware store to be sure whether you have a faulty nut or not.
  • While you're there you can connect a threaded rod with nuts there to gain experience what the typical degree of freedom in this union is.
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