zeroing machine to fixture causes motion

after positioning my 3 axis gantry router at the fixture reference point, I use the "touch off" button to set the position to "0.00" for each axis. Often, but not always the "Y" axis will move when I enter the position. It doesn't have to be the "Y" axis I'm setting and it only happens once. The Axis display doesn't show this movement. I'm using Axis 2.4.6 using linux 8.04

I'm using a 3 axis Hobbycnc board that seems to work great, and I don't seem to loose steps during any of my runs.

Please tell me what configuration setting I have managed to mess up.

Thanks

John Lindsay

Hello John,

How far does it move? Do you have backlash compensation turned on? If so have you tried it with the backlash compensation off?

Rick G

Sorry for being out of touch after asking the question, I think this started happening after I turned on Backlash compensation. after looking at the problem it would appear that the movement isn't all that much, but I do have a lot of backlash in my lead screws presently, and I'm replacing the screws with ball screws in the next few weeks.

I bet that will take care of the issue.

Thanks for all your comments.

John

Pretty sure I have seen this behavior on set ups with large backlash compensation.
Not really sure if it ever caused any problems, I believe it is EMC applying the backlash compensation to one side or the other of the Axis.
Let us know how it works out with the new hardware.

Rick G

Hello John,

That makes sense, I believe I have seen the same behavior after a G92.

Rick

Thanks for the comments, I'm almost happy to find that I didn't cause it.

Thanks everyone

Just a quick note, that after replacing the Y axis screw, I eliminated the backlash compensation on that axis, the the problem didn't return.

Thanks to everyone.