1 Topic by Kvirre

  • Kvirre
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Topic: Backlash from bent sprocket-mount?

Hi,

From what I understand some of you experience y-axis-backlash problems.
So do, and I went about this the same as most did, tension the belts ....

Ok, so this did not help at all, it actually made things worse, why?
Well I suspect that I bent (or may be was already) the frontal belt sprocket-mounts.

Please see my attached picture if you feel unsure of what I mean.

-------------------------------------------------------------------------------------------------------------------------------------------------

Now why would I suspect that it's bent .....
Well, if I study the belts from above (birds-perspective) I see that they go inwards on the front of the machine.
There is headroom for the sprocket to move and correct it's position (back out), but they do not, simply because the rod where the sprocket is located on, is not parallel.

So would this be an reasonable exploitation for my backlash?

The backlash is on a 10x10 mm cube :

x : 10.02 mm (almost perfect)
y : 09:47 mm (horrible)

And it's constant more or less ...

Please help

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2 Reply by elmoret

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Re: Backlash from bent sprocket-mount?

What happens when you loosen it back up? If it's too tight, the friction will be too much for the steppers to overcome, and they will miss steps.

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3 Reply by Kvirre

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Re: Backlash from bent sprocket-mount?

Tried that, did not help.

They are constantly on their inward position.
If I move the mount with my finger to make it parallel, it slides right out to its proper position.

They are bent .... that's it.

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4 Reply by elmoret

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Re: Backlash from bent sprocket-mount?

Sounds like the plastic is bent permanently. You could print new ones, easy enough (though SD won't release the STLs for any parts).

Have you tried the backlash compensation in software?

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5 Reply by Kvirre

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Re: Backlash from bent sprocket-mount?

I have tried it, or at least I did put

M99 X0 Y0.17 Z0 E0

in the start g-code, but I don't know if that was the only thing I needed to do.
(did not work)

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6 Reply by Kvirre

  • Kvirre
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Re: Backlash from bent sprocket-mount?

There I fixed it ....

found a thin metal wire i bent to a "L" shape and stuck it in the right position.
Now the mount is leveled and belts are parallel to the rod.

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7 Reply by ronsii

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Re: Backlash from bent sprocket-mount?

Kvirre wrote:

There I fixed it ....

found a thin metal wire i bent to a "L" shape and stuck it in the right position.
Now the mount is leveled and belts are parallel to the rod.

So, did this fix the backlash problem or just the bent part problem?

8 Reply by Kvirre

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Re: Backlash from bent sprocket-mount?

First attempt says no.
sad

But I already suspected that.
Now I will try the belts again, but doing the corrections less aggressive.

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9 Reply by HelmutK (edited by HelmutK 2012-11-10 15:31:31)

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Re: Backlash from bent sprocket-mount?

Both of my front belt mount assemblies are also like that and the belt always rides on the sprocket towards the outside of the case. But I have been printing fine for two months and do not see any apparent wear issues. I think this may be a possible part of a potential printing issue for some but not a sole cause.

10 Reply by IanJohnson

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Re: Backlash from bent sprocket-mount?

To really dial this out, I think you are going to need a dial indicator.  Between the movement of the axis and your measurements there is generation of gcode, and the extruder's execution of the gcode.  You might be chasing a problem that isn't Y backlash, or the amount of backlash that you think it is, since you are measuring it indirectly via the size of the finished part.

Playing around with mine some more this morning, I found that I can dial the backlash up and down with the tension of the Y motor.  When I got the backlash to .03 with the back belt, I started getting binding at the front of the platform.  I found that loosening the side belts by a full turn relieved the binding without increasing the backlash.  I also found that where a 10mm move command got  a 10.01mm move, after loosening the belts it was 9.93.  It was still consistent, and with low backlash.  I'm not going to quibble with .07mm, the actual extrusion of plastic isn't that precise.