Y axis shifts 2" in the middle of cutting

[twall7407]

I am cutting a mold in 6061 aluminum on a 440. During my 2nd operation (1/4" flat EM adaptive) the machine seems to loose track of where it is on the Y axis and shift 2" positive and starts cutting in the wrong spot. Once I see its in the wrong position, I stop the machine and give it a home (G0X0Y0) and it homes to the wrong location 2" positive in the Y. If I then re-reference it to the Y limit switch and home again, it returns to the correct home position.

Any ideas on what's causing this? Is my Y axis stepper slipping for some reason? I tried reducing the feedrate in half and got a very similar result.

Thanks!!
Todd

[Mooser]

Seems that it's loosing a little each time on a lot of movements. I'd be tempted to check the motor to ballscrew connector to see if it's loose or slipping.
M

[soofle616]

What is your feedrate set to? Steppers can lose steps for a lot of reasons, two of the more common being too much torque required to complete the move and too high of an acceleration ramp. While I would not expect the acceleration thing to be an issue since the machine has built in parameters to limit that, the combination of the two might be causing incremental shifts as Mooser suggested. Have you checked any of the dimensions on the features that are made prior to the move that results in the Y-axis shift? Is anything under or oversized or out of position?

[Bill_B]

Im learning a 440 at work and had the same issue right away. Turns out just the chip build-up in the billows can cause skipped steps, go figure I would have never thought that but yes. I thought I was loosing my mind trying to figure it out, NO crashing and still was getting skipped steps resulting in origin in the wrong place. Keep those billows clear of chips, I have and its helped for sure. I think the steppers are pretty weak not sure what ones they are. I'm going to add covers on both ways from and back like they have for the 770 & 1100 machines, they do not have covers for the 440 tech did not know why?

In fact Im going to add clear covers so I can keep an eye on the chip build-up underneath the covers I am going to install. Tormach ones are black sheet rubber I think clearn will be better. 1/8 thick clear vinyl is what I will use.