Z cutting deeper the more time goes by ??? - Page 9

# Thread: Z cutting deeper the more time goes by ???

1. ## Re: Z cutting deeper the more time goes by ???

What if you slow down all Z Rapid move's...say make them a G1 at Feedrate of 25-50 IPM See if the problem disappears.

2. ## Re: Z cutting deeper the more time goes by ???

I'm confused. If the Z axis is cutting deeper than commanded, wouldn't that indicate an excess of pulses, or gaining steps (assuming nothing mechanical, like a slipping coupling)? I can't get my head around how lost steps would fit in this scenario.
When the Z axis stalls while retracting, or lifting, it ends up lower than it's supposed to be. So the next move down will be deeper.

3. ## Re: Z cutting deeper the more time goes by ???

Yes, I'm leaning toward the loosing steps direction I looked at the code and didn't see any thing weird. I thinking an optional stop (m1) at each z retract between each letter and measure the z and compare to the readout and ( like somebody said earlier ) see if its random or a consistent amount and if happens in one spot or grows worse as it runs.

4. ## Re: Z cutting deeper the more time goes by ???

This is a standard test.
Set up a Dial Indicator on the table and put a square-ended bit of metal in the spindle.
Lower the spindle until you have a reading on the DI.
Now cycle the Z axis up and down 50 times and see if and how the DI creeps.

If it suddenly jumps - um, interesting.
But if it just creeps steadily, then you are picking up or losing Z axis Step pulses on every direction change.

Cheers
Roger

5. ## Re: Z cutting deeper the more time goes by ???

Originally Posted by RCaffin
This is a standard test.
Set up a Dial Indicator on the table and put a square-ended bit of metal in the spindle.
Lower the spindle until you have a reading on the DI.
Now cycle the Z axis up and down 50 times and see if and how the DI creeps.

If it suddenly jumps - um, interesting.
But if it just creeps steadily, then you are picking up or losing Z axis Step pulses on every direction change.

Cheers
Roger
Roger,

He tried 20 up/down cycles each at 15 IPM, 30 IPM and 60 IPM (60 cycles total). I have attached what the OP prepared showing the results. An increase of .0005" on the down stroke in the 10th cycle at 30 IPM is a bit odd, but it remained constant for the last 10 cycles. I'm not sure I would consider it a significant anomaly, since is consistent for the other 40 cycles, and it's only .0005". I'm guessing that the .0005" change had more to do with the dial indicator than with the machine. I have one that has .0005" resolution, but it's not accurate to .0005".

Do these results meet your suggestion , or do you endorse giving it another go, only doing 50 continuous cycles at a fixed velocity? Do you have a velocity recommendation? As noted, when the problem showed up, he was running Z at only 5 IPM. Maybe he should run at that speed to simulate what happened during actual production?

Gary

6. ## Re: Z cutting deeper the more time goes by ???

Originally Posted by ger21
When the Z axis stalls while retracting, or lifting, it ends up lower than it's supposed to be. So the next move down will be deeper.

Forehead slapping senior moment. It's the same effect as a slipping coupling attached to the screw. I'm embarrassed that it wasn't obvious to me. It should have been. Thank you for getting me back on track.

Gary

7. ## Re: Z cutting deeper the more time goes by ???

Hi Gary

That data says to me that it is NOT an electronics problem (as I had previously suggested).

Cheers
Roger

8. ## Re: Z cutting deeper the more time goes by ???

He tried 20 up/down cycles each at 15 IPM, 30 IPM and 60 IPM (60 cycles total).
That's not a good test for lost steps.
Lost steps on the Z axis will typically happen with lots of rapid, back and forth random movements, like 3D carving.

9. ## Re: Z cutting deeper the more time goes by ???

No News ....This might help if, you tweek Z axis Motor
https://www.machsupport.com/wp-conte...all_Config.pdf

Page 77 of 106 pdf
or
5.5.2 Motor Tuning and Setup ..page 5-19

Good Luck,
DJ

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