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Prusa Mendel i3 y axis tolerance/problems

Posted by foul_owl 
Prusa Mendel i3 y axis tolerance/problems
May 23, 2014 05:58PM
Hi folks,

I'm in the process of calibrating my new Prusa i3. Printing the 20mmx20mmx10mm test box.

Here is the result:

The tolerance along the x axis is fine, but it looks like the tolerance along the y axis is not good.

Tried doing a second print of the same object:

So it looks like the y axis has some issues. However:
1. y axis belt is definitely tight. I have the tensioner in place, and I tightened things up before printing each time.
2. y axis motor is calibrated. I followed the calibration instructions, and I can move it around with pronterface without any stuttering or noise.

While watching the prints it looked like the y axis was getting stuck perhaps.

Definitely open to try anything as well. Maybe there are some settings in the Marlin config I need to tweak.


From trying to move the y axis back and forth with my hands, it definitely feels like it is sticky in certain places. Any ideas on how to fix that? I aligned the idler, motor mount, and carriage mount pretty well I think.

1. Belt is held in place (partially) with zip ties. I tried tightening the belt a bit more, and one side popped out of the zip ties:
Any better options there? Zip ties seem like a pretty stupid idea, to be honest.

2. Y carriage is held in place with zip ties as well. See:

This allows the plate to rotate in either direction by quite a bit. Any better options there as well? Thanks!!

I have tightened the zip ties in both cases with needle nose pliers.

Edit 2:
I realized as well that it looks like the teeth on the belt holder don't match the teeth of the belt, but I bought this as a kit, so I didn't think too much of it.

Edited 2 time(s). Last edit at 05/23/2014 07:32PM by foul_owl.
Re: Prusa Mendel i3 y axis tolerance/problems
May 23, 2014 09:44PM
My printer is different than yours, but I put a half-twist in the belt before the idler and mesh the belt ends together tooth-to-tooth inside of my x-carriage, holding them together on the outside with zip ties. Something like [hydraraptor.blogspot.com] , but with my carriage between the wired bits.
Re: Prusa Mendel i3 y axis tolerance/problems
May 24, 2014 08:41PM
Interesting idea! I might give that a try.

I looked closer at the zip ties, and they were so loose that the bearings could actually slide around under them. I tightened them when I originally installed them, but I think they might have loosened up a bit. I replaced them and tightened with needle nose pliers again.

At any rate, I think relying on zip ties being tight for accuracy in one of the dimensions is a terrible design decision. Considering going with something like this:
$10 is not a bad price to pay to save on maintenance (tightening the zip ties every few weeks) and time lost banging my head against the wall trying to figure out what's not working.
Re: Prusa Mendel i3 y axis tolerance/problems
May 25, 2014 01:07PM
Make sure the pulleys are tight i filed a flat on the stepper shafts, binding on the y make sure the smooth rods are all squared up with the corners what i did is hand taught each corner and tightend up the corners while checking how freely the y moved made adjustments as needed

Check my rubbish blog for my prusa i3

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