ghost movement on y axis

[fast89]

I've got a Bridgeport mill that i converted years ago. I've had a problem for quite a while now but it's starting to get on me nerves. When the machine is homed out (x0 y0 z0) the glass scales read 0's too. When the table is brought back to center (x-10.), the y axis moves -.002". I was absolutely convinced it was a mechanical issue. I repositioned end brackets, ballnuts etc with no luck. My stepfather thought it was electrical. To this, i unpowered the y axis and did the same test rolling the x axis back to center. Well whaddaa ya know, there was no movement on the y axis, it is electrical. I've tried everything i could think of to pinpoint the electrical problem. Encoder cable is shielded and grounded to the power supply/servo drive enclosure, i seperated the encoder/motor wires. Anyone else ever see a problem like this. Maybe i need to invest in some shielded motor wires. My y axis motor has always been a bit noisy despite whatever tunning i have tried. Maybe ive got a motor/encoder/drive issue?

[jimglass]

Could be cross talk between AC power and the steppers. Is there any AC wires or AC motor near the Y axis cable?

Jim

[Brenck]

Do you use a inverter on it? They make a lot of interference, if you say the enconder cables are shielded its probably the AC cable from spindle, you should shield all cables so you can eliminate one probability, but if you use an inverter or the VFD is inside the same box with all the electronics try to take it out and run to see if the problem still occur, you dont need to actually take it off you can just plug it off and run with no energy going to the inverter.

I had a problem with mine and just solved when I took the cable from the spindle off the cable organizer, looks like they cant run close from the steppers/servo cables

Take a look this will help you http://www.cnccookbook.com/CCCNCNoise.html