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General Mach Discussion / Z Axis Drift With Servos...I Don't Understand It
« on: January 04, 2021, 06:04:29 PM »
Hello there Mach world! Long time listener, first time caller here.
I've got a problem on my hands that I can't seem to sort out on my own. I've tried to read through all the posts in all the different amateur support groups that I can, but I now I think I need some help from the pros. I'll try to explain all of this in as best of detail as possible.
Basically what's happening is this:
When I run a G-Code in Mach3 that requires a lot of up and down movement in the Z and a fair amount of travel in the X or Y...I have noticed that by the time my program is through, and my spindle and bit return to my Zero position, the Z axis has drifted upwards a small amount to a new location. But the DRO still reads that it is in the correct position (X0, Y0, Z0). And this happens even when the machine is running in the air and there is no material being cut.
The distance that is lost in the positive Z direction seems to have a direct correlation with how much movement takes place in the Z axis.
For example:
If I run a 3D Finish raster carving with a .125" ball nose with a stepover of 10% - the Z axis will lose it's position by say +.5" (arbitrary number).
And if I run the exact same carving with the exact same bit with a stepover instead of 5% - the Z axis will lose it's position by double the amount and wind up 1" higher than my original Zero position.
This proves to be true for any program, any bit, any raster direction, feed or speed, any time of day, etc... I have even tried swapping the Z motors with one from X or Y and the problem still persists.
I have tried greasing and lubing everything, tightening everything that I have access to, and changing the acceleration, the feed rates, and the Step/Dir Pulse values from 0 - 8.
I was doing some reading through other posts here and it seems this gentlemen was having the same issue as I am:
https://www.machsupport.com/forum/index.php?topic=2749.0
but he has a different controller than I do and I can't seem to find any information regarding a multiplier board on a PMDX-126 or a SmoothStepper. Admittedly, I do not know what a multiplier board is, so that doesn't help my cause much.
Here's a little info on what I'm running:
5' x 10' Precix (Chinese) CNC
Rack and Pinion
Ball Screw Z
PMDX-126 with a SmoothStepper
Delta Drivers and Servo Motors
Mach3 on Windows 7
And my G-Code is being created by the "Mach2/3 Arcs (inch) (*.txt)" post processor in Vectric Aspire on a separate MSI computer running Windows 10
I'm going to attach a compressed copy of a G-Code test program that I'm running today. It seems to give me a repeatable loss in Z of about 3/16".
I hope this all does a good job of explaining my issue clearly. If there is anything at all that any of you guys might suggest for troubleshooting I would greatly appreciate it.
Thank you all in advance!
Tim
I've got a problem on my hands that I can't seem to sort out on my own. I've tried to read through all the posts in all the different amateur support groups that I can, but I now I think I need some help from the pros. I'll try to explain all of this in as best of detail as possible.
Basically what's happening is this:
When I run a G-Code in Mach3 that requires a lot of up and down movement in the Z and a fair amount of travel in the X or Y...I have noticed that by the time my program is through, and my spindle and bit return to my Zero position, the Z axis has drifted upwards a small amount to a new location. But the DRO still reads that it is in the correct position (X0, Y0, Z0). And this happens even when the machine is running in the air and there is no material being cut.
The distance that is lost in the positive Z direction seems to have a direct correlation with how much movement takes place in the Z axis.
For example:
If I run a 3D Finish raster carving with a .125" ball nose with a stepover of 10% - the Z axis will lose it's position by say +.5" (arbitrary number).
And if I run the exact same carving with the exact same bit with a stepover instead of 5% - the Z axis will lose it's position by double the amount and wind up 1" higher than my original Zero position.
This proves to be true for any program, any bit, any raster direction, feed or speed, any time of day, etc... I have even tried swapping the Z motors with one from X or Y and the problem still persists.
I have tried greasing and lubing everything, tightening everything that I have access to, and changing the acceleration, the feed rates, and the Step/Dir Pulse values from 0 - 8.
I was doing some reading through other posts here and it seems this gentlemen was having the same issue as I am:
https://www.machsupport.com/forum/index.php?topic=2749.0
but he has a different controller than I do and I can't seem to find any information regarding a multiplier board on a PMDX-126 or a SmoothStepper. Admittedly, I do not know what a multiplier board is, so that doesn't help my cause much.
Here's a little info on what I'm running:
5' x 10' Precix (Chinese) CNC
Rack and Pinion
Ball Screw Z
PMDX-126 with a SmoothStepper
Delta Drivers and Servo Motors
Mach3 on Windows 7
And my G-Code is being created by the "Mach2/3 Arcs (inch) (*.txt)" post processor in Vectric Aspire on a separate MSI computer running Windows 10
I'm going to attach a compressed copy of a G-Code test program that I'm running today. It seems to give me a repeatable loss in Z of about 3/16".
I hope this all does a good job of explaining my issue clearly. If there is anything at all that any of you guys might suggest for troubleshooting I would greatly appreciate it.
Thank you all in advance!
Tim