The Original Prusa i3 MK3 is the successor of the award-winning Original Prusa i3 MK2 3D printer.

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Problem with trapezoidal nut

I just received my MK3 kit and started putting it together. Things went well until I reached "Step 77 Assembling the X-axis and smooth rods" step on the Z-axis assembly guide.

One of the two trapezoidal nuts is not turning easily. One of the nuts can be rotated with one finger smoothly down the lead screw but the other requires significant work to turn at all. I took the nuts off the x-axis to make sure there was not an alignment issue. The one "good" trapezoidal nut spins easily on both lead screws, but the "bad" nut does not work well on either.

I don't know if the part was defective or if i messed up the threads, but i need a new trapezoidal nut to continue assembling the kit. I emailed support but have not received a response yet. How do i go about getting a replacement trapezoidal nut?

I'm hoping to get a replacement sent out as soon as possible so i can continue assembling the MK3.

Any help or guidance would be appreciated.

Thanks,

Christopher Dopp

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Thanks for your responses guys. Unfortunately, I don't have another printer to create a replacement part with. It took a few interactive chats with the support team, but they have shipped me out a set of replacement trapezoidal nuts. I did not receive any email confirmation from Prusa (even after the chats) but did receive a shipping notice and tracking number email and phone call from DHL. The replacement nuts should arrive this Friday.

I originally sent an email to support which I never received a response to. (I think by the time they read the email I had chatted with support a few times.) Tip: if you are using an ad-block extension your browser (like Ghostery which I highly recommend.) you need to make sure the interactive chat tracker is on so the button to start a chat is available.

So I would say be patient and reach out via the interactive chat a few times. While a confirmation email that the parts have been ordered would have been appreciated, they did send out the part as they said they would.

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The replacement trapezoidal nut from Prusa arrived. After replacing the badly threaded one with the replacement everything ran smoothly. Calibration and printing is working now. Now i just need to learn how to adjust it to get the best prints possible. Anyway, if you have a bad trapezoidal nut chat with support a few times and they will send a replacement. Good luck everyone and thanks for the answers.

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I went ahead and assembled the rest of the kit as I wasn’t sure if it was a complete blocker for the printer to work. (It was. ) Replacing a nut was really simple. Unscrew 2 screws holding the Z axis at the top and the two screws on the trapezoidal nut itself. Unscrew old nut (still took effort), replace with new one (gently, very carefully) which fortunately went on easily and correctly, 4 screws and the onto calibration. Everything else worked fine. Good Luck.

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5 Answers

I had the same problem. I used the chat window in the online manual to get some help. They are (supposedly) sending me a replacement. But that is going to take a while.

I did finish the build printing a replacement. If you have another 3D printer, this could work for you as well. I printed the following:

https://www.thingiverse.com/thing:224650...

I printed in eSUN PLA+ since I don't have any Nylon filament. It seems to be working great for now. Clearly nylon would be better, but it is getting me by until I get the replacement.

I hope this helps.

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I have this problem as well. Both nuts unthreaded off the rods easily, so I know they were not damaged. I think there’s something [I don’t know what] that makes it easy to cross-thread one of the trapezoid nuts when putting them back on. I should have realized this at the time and not forced the nut onto the rod, but now the damage is done and I’ll need a new one. I commented in the manual to maybe add a warning to check the threading if any resistance is felt.

I also sent an email to support but have not heard back from them, and it’s been about a week. Will give the chat window a try next. I don’t have access to another printer, so I’m dead in the water until I can get a replacement part.

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I also have this issue. Interesting that 3 people (counting me) have noted this issue within a week or so. Unlike Tony, I believe my tight trapezoid nut was tight even before I took it off the first time during assembly.

There is a very noticeable difference in force needed to rotate the two Z-axis screws. I partially disassembly each side, to determine that the force needed was due to the trapezoid nut, and not the motor itself.

I tried generous lubing with Super-Lube and it helped a little, but is still noticeable.

Christopher apparently had issues with calibration. I'm not that far with assembly, and intend to try it as-is in case the parts will "break-in/wear-in". If I have issues with calibration, I will follow Christopher's advice to use the online chat.

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This just happened to mine. Need to contact Prusia for a replacement part I guess... Was it the right side for everyone?

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It was the left side for me, the nuts are identical so I think it’s just random chance for it to cross-thread. Most important is not to force it if you feel any resistance.

I did get a replacement from Prusa and was super careful putting it on. Everything working perfectly now.

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Can you print with ABS or PETG? Also, does anyone know why this is a plastic part instead of brass and is there a suitable brass replacement for longer wear life?

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This is open source so you should be able to get a nut online. Just make sure it your, size, pitch, and trapezoidal. I am not a mech engineer. I would not print this but get a replacement pair from prusa for free. then sent them to me for free.

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I looked at other posting most did not have good printing results with brass too much play in the axis.

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Christopher Dopp will be eternally grateful.
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