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?

Try reducing your Z axis Acceleration and Velocity (in motor tuning) by 50% and apply the changes. Does the problem still occur ?

Tweakie.

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.

What are the Acceleration and Velocity figures you are currently using ?

Tweakie.

Hi

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

thanks

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

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

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.

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

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.