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Z axis inconsistent movement
« on: September 03, 2020, 06:07:27 PM »
Z axis inconsistent movement

My Z axis is creeping upward during the program run.
I have run the following gcode with a repeatable error.

The original location of Z 0
Code Run
Z10
Z0
Will give me a Z offset of +0.002mm each time I run it. But Mach 3 display is Z0.

Original location of Z 0
Code Run
Z5
Z10
Z0
Will give me a Z0 each time I run it and Mach 3 display is also Z0.

Basically start at Z0 with Z10 Z0 will give me an error in Z but Z5 Z10 Z0 will be correct.

Does anybody know how to fix this?

Offline Tweakie.CNC

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Re: Z axis inconsistent movement
« Reply #1 on: September 04, 2020, 12:57:25 AM »
Try reducing your Z axis Acceleration and Velocity (in motor tuning) by 50% and apply the changes. Does the problem still occur ?

Tweakie.
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Re: Z axis inconsistent movement
« Reply #2 on: September 04, 2020, 01:01:01 AM »
Try reducing your Z axis Acceleration and Velocity (in motor tuning) by 50% and apply the changes. Does the problem still occur ?

Tweakie.

Yes, have tried that. Even to 10% it still has that. The odd thing is if I do step up or step down it does not have any error. Z5 Z10 Z15 Z20 Z0 will give me no error. Z20 Z0 will give me a consistent error each time I run it.

Offline Tweakie.CNC

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Re: Z axis inconsistent movement
« Reply #3 on: September 04, 2020, 01:27:28 AM »
What are the Acceleration and Velocity figures you are currently using ?

Tweakie.
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Re: Z axis inconsistent movement
« Reply #4 on: September 06, 2020, 05:01:16 PM »
Hi

My acceleration is 150mm's and velocity is 2800mm's

thanks

Offline RICH

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Re: Z axis inconsistent movement
« Reply #5 on: September 07, 2020, 07:31:22 AM »
Will give me a Z offset of +0.002mm each time I run it.

0.002mm  = 0.000079"
What is your theoretical and actual resolution for the Z axis ?
How are you measuring that error?
How is that axis driven and are the axis components of dimensional quality ?

Just a few practical considerations.

RICH
Re: Z axis inconsistent movement
« Reply #6 on: September 07, 2020, 04:32:23 PM »
the 0.002 is an averaged number. as I did repeated z5 z0 10 times it becomes 0.02. I have also done z5 z10 z0 10 times it has no error.

thanks

Offline ZASto

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Re: Z axis inconsistent movement
« Reply #7 on: September 08, 2020, 04:39:23 AM »
If you repeat your "problematic" sequence 100 times, what is the result?
How do you measure micrometer difference? I guess that the resolution as well as repeatability of your machine is much worse than 2um.
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Re: Z axis inconsistent movement
« Reply #8 on: September 08, 2020, 05:33:57 AM »
If you repeat your "problematic" sequence 100 times, what is the result?
How do you measure micrometer difference? I guess that the resolution as well as repeatability of your machine is much worse than 2um.

my machine have about 0.01 resolution.

I'm measuring using a dial indicator. I fixed a dial indicator to the bed with the indicator pin to the bottom of the spindle shell. marked that as Z0.

I can see a noticeable change every time I run Z10 Z0, which raise Z to 10 them back to 0.  it has a consistent change of the Z hight each time I run the code. It averages out about +0.002mm. I have set up the code to run 100 times it had about +0.19mm in Z hight.
With the same setup, the code Z5 Z10 Z0, which raise Z to 5 then raise to 10 them back to 0. it has no noticeable change of the Z hight regardless now many time I Run the code. I have run the code up to 200 times it had no change to the Z hight.
I have also run the code Z5 Z10 Z5 Z0 , which raise Z to 5 then raise to 10 them back to 5 then back to 0. it also has no noticeable change of the Z hight hight regardless now many time I Run the code.

Thanks

Offline Tweakie.CNC

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Re: Z axis inconsistent movement
« Reply #9 on: September 08, 2020, 06:21:26 AM »
Perhaps one more test you could do is zero your Z axis to a gauge block (any solid block would do) – carefully slide out the block – run your test 100 times – slide in the block – measure the gap with feeler.

This would verify the integrity of your dial indicator.

Tweakie.
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