Hi,
I have a very odd problem going on with my cnc z axis, It usually runs fine. But when I ran the machine longer than 2 to 3 hour. The z axis motor slows down automatically and vibrate like crazy. Then some time it goes away and the cnc moves fine and then after some time it started to vibrate and slow down again. Even though i don't change the speed it just happen automatically. what is the matter you think? Have you came across anything like this before.
Thx.

Is the Z actually slowing down or does it just sounds that way?
If it was slowing then it would be reasonable to think it was partially stalling and as such you would be losing position on a stepper system. Are you losing Z position?
If it just sounded like it was slowing and you are not losing position then it is not so bad.
Likely cause is the axis expanding with the friction from running extended periods, you may find that it is binding slightly due to this and you really want to find out where the problem is and rectify it. Could be as simple as needing to adjust the alignment of linear rails or or adjusting gibs or whatever it uses

Hood

Is the motor getting hot?

RICH

Are you losing Z position?
Hood

Yes as i was running a code I cuts well but after a while the motor started to slow down and showed vibration. so I stop the machine did a regular jog even though it was showing 150ipm on mach3 it was not doing 150, But it waited like 15min then tried it was actually running at 150.
Also while it was slowing down, z was losing it postion wasn't cutting right. I was cutting a 2inch piece and it started to go depper than that and thats when i stopped and realized. This has happened to me before but its like the next time I turn my machine it works fine for couple of hours then goes bad.

@rick yes the motor is getting hot but it a normal hot not crazy hot.

I have had steppers that were rated for the amperage that was set but when they got hot to the touch, lets say 140 to 160 F they started acting weird. They were running below rating but no longer were reliable. So that's why asked.

RICH

Sounds like the axis is heating and binding bit could also be the motor heating as Rich mentioned or even possibly the drive itself overheating.
Hood

You just may be expecting too much from the stepper at 150 ipm.  As the machine heats up, a very slight binding of anything from expansion may be more than the stepper can handle at that speed.  Slow it down to 100 ipm and try it.

John Champlain

Also check to see if the drive is getting hot.