Thread: Mysterious Z axis errors
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30-03-2017 #1
Hi everyone,
Started routing a piece of plywood using UCCNC, with a cut that is uniform and parallel from end to end, to find that my Z axis is loosing position as it moves along the piece.
The first time I was running constant velocity mode, with max acceptable error of 30 microns. I ran 95cm in length, the Z error was actually to push the Z axis into the piece further ( create a deeper cut ) , and over 95cm, I had a change in Z position of about 1 to 2mm deeper cut.
The second time, I changed the constant velocity mode max error to 50 microns, decreased the Z axis max acceleration by 60%, and max speed to 30% to discount the motor missing steps due to load at higher speed/accelerations. This time the Z errors appeared to occur much faster, and after about 20cm, the Z had plunged down an extra 4.5mm.
The G-code is correct, and I confirmed that without running the program, jumping from start to finish showed that the work was 4 to 5 mm deeper at one end vs the other.
My thinking is that it somehow has something to do with Constant velocity mode ( although this is not supposed to create compound errors, just errors between point a and point c ) - or my controller not hacking it, or not providing enough holding power sometimes ( G540 )
The wierd thing is, when I slowed down the z axis and accelerations, it got worse - which you would think would make better if it was a load related issue?
Still wainting the leadshines to arrive, so need to persist with the G540 for now
Any ideas?
Nick
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