Regarding leaning Idlers & "Belt Walk"

questions and tips related to specific components

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kraegar
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Regarding leaning Idlers & "Belt Walk"

Post by kraegar » Tue Sep 18, 2018 4:43 pm

One issue that has come up has been with the idler mounts (and to some extent, the X carriages). What we've found is that over time the printed parts can deform from the stress of the belt tension. This will allow the idler bolts to lean.
When they lean, the belts ride up on the idlers and rub on the top of them. The teeth grabbing the top edge of the idler cause the belt to lean in and out as it changes direction, very subtly changing the belt length. In prints it creates artifacts in X/Y.

We tried different versions of printed idler mounts and X carriages, and they can solve the problem for a while, but within 1 - 3 months, the bolt will lean again. The print issues, while minor, are frustrating. We tried CF petg, PLA, CF PLA, PC and CF PC. Eventually all of them will lean, though some last longer than others.

So we've worked with 713maker to come up with a solution specifically for the idler mounts. I know people have been waiting on these, and we finally have it. The solution was to ditch the design used for the printed parts, and go to a flat plate similar to the stepper mounts. We then paired that with high quality steel shoulder bolts. This means the idler stacks won't lean, and the belts don't rub. Steve received his idler mounts yesterday, and I got mine today for testing. They are rock solid, and won't change over time.

Going forward, I recommend either purchasing the aluminum mounts, or being aware that you may periodically need to reprint your idler mounts.

To full put the issue to rest, we're working with another maker, and hole to also soon have machined X carriages using the same shoulder bolt approach available.

This one took a while to solve, but I think it's finally done (and I think the idler mounts look fantastic... and will also allow for a top to be put on easier).

Thanks to Matthew White at 713Maker.com for all the help in tracking down this issue, through MANY iterations of idler mount designs.

Image




tiz.io
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Post by tiz.io » Thu Jan 10, 2019 10:53 pm

A self-described "expert" on belt-driven printers suggested that securing the idlers on only one side is sure to create problems over time, even if they are mounted to metal plates. In the 4 months since you made this post, would you say the new metal parts were sufficient to permanently solve this problem?


Topic author
kraegar
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Post by kraegar » Thu Jan 10, 2019 11:47 pm

I've seen zero evidence of the idler stacks leaning. The shoulder bolts haven't deflected, nor have the mounts. I don't see the belts rubbing on the top of the idlers at all.


tiz.io
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Post by tiz.io » Sun Jan 13, 2019 5:15 pm

Excellent, I imagine it would take a lot of tension on that little belt to actually bend an M3 like that.


tiz.io
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Post by tiz.io » Mon Jan 14, 2019 5:49 am

I've been studying the design and have been unable to determine if I'm missing something here:
What's stopping someone from stacking both belts on the same vertical post in the picture above? If you had a thrust bearing between them and did the same for the X carriage idlers, would there be any other problems I'm not seeing?


justinsgray
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Post by justinsgray » Mon Jan 14, 2019 5:50 pm

Over on the facebook group, someone was testing oversized lower pulley. They mounted it on the same shoulder bolt. Honestly, I was wondering the same thing. Im sure there is a reason for this, but I don't know what it is


tiz.io
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Post by tiz.io » Wed Jan 16, 2019 4:29 pm

Nice.
Here's another good coreXY design with stacked pulleys:

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