WHAT IM USING: I have a cheap ebay machine (waiting on a shipping quote to buy a Taig) and i'm trying to face down some 5mm think aluminum stock to 2.25mm using a 2.76mm endmill. I'm using a rhino cam, and a 2.5 axis climbing cut island path. My entry is a 3mm arc on the Y-X+ side of the stock, with the 0,0 on the top left corner. I'm taking 1mm per pass, at 30% stepover with two .02 finishing passes, IIRC.
PROBLEM:I touch off at the 0, home and 0 everything in mach 3, and off i go. From there it picks up to 1.57, rapids to the arc entry point, and starts the arc into the side of the material. Z and X are fine except the Y axis doesn't move as far as mach3 is saying it is. Now, when the machine goes on it's tool path, it cuts the arc, then X-,Y+,X+,Y- back to where the arc stopped, and it hits back to where it started perfectly each time. But between levels, it picks up and goes to another arc, and misses short, towards the Y+ side everytime.
WHAT I'VE TRIED: So far, I've tightened the couplers, checked for slop in the Y by putting a mic on the shaft and moving it +-+-+-+ and it's not moving in/out as if theres a thrust bearing issue. I've calibrated all axises, to within .0005" including setting backlash (my mic reads inches but I convert to mm for calibration) and everything is right.
It sounds like you're losing steps in Y. When it does all this, and you command a move back to Y=0, what happens? Does it go back to where it started, or someplace else? If it is lost steps, try reducing the acceleration values in Motor Tuning (cut them in half or so), and try again.
That's what confused me so much. After I posted this I tried checked the calibration again, and it was fine, changed the accel, same thing, and when i would start at a point and 0 everything, then move it about, and tell it to return to 0 it was fine. Only when it was cutting did I have this problem.
SO, I started messing around with it, and turns out my Y axis coupler was loose, causing it to drag around as it was cutting. The motor shaft had a flat ground onto it, but the leadscrew does not, so it tends to slip from time to time, i think because the vibrations cause the setscrew to slowly back out. It wasn't so loose as to cause it to slip while jogging or calibrating it, but only while cutting or so it seems.. So i pulled it apart, tightened everything up, and hopefully that will solve the issues. I've got duty today, so I'll try some more tomorrow afternoon when I leave work. I'll keep you updated. Thanks for your help!
That would certainly explain it. Cutting forces can be considerable, and will push things around a lot more than mere jogging. See if you can put a flat on your screw as well, or go to a clamp-type coupling instead of the setscrew type.
Y axis problem...Please help!
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