Centroid Community CNC Support Forum

Figured I would post here since I really can't seem to narrow down this problem.

I'm using clearpath motors with 1616 ballscrews. I've had this problem before where the Y axis makes a weird noise and is harder to move on one side. First time i came into the problem was because my motor got into protection due to RMS max being reached. Turns out the screws holding my ballscrew nut came loose and this was causing the issue. Tightened it back and no more problem... I was running 600ipm cuts with this machine without issues and Y motor RMS staying in the 50-55% range.

Now I moved into a new workshop, reassembled the machine and the problem comes back. However, I can't seem to narrow it down. I tried moving the ballscrew nut, greased everything, undid every part to make sure they were moving fine, checked squareness of the Y axis, checked tightness of everything... I really don't see anything wrong. I even went under the machine with the MPG in hand to move it and see if there was any vibrations or anything special and nada... It really seems to be coming form the X- side Y axis.

Here's a link to a youtube video for reference : https://www.youtube.com/watch?v=tiGYQHxBOgc

Any recommendations?

I think if you post pictures of the offending part of the machine we might be able to give some ideas.

Are you saying the nut comes loose, binding occurs and then the Clearpath motor faults?
Have you disconnected the motors and manually turned the ballscrews the full length of their travel to find out what part of the machine, the issue occurs? Are the linear guides exactly parallel and with each other?

Without a little more information, it's hard to picture what might be happening

Marty

You might be better served to make a file that moves the y axis from one end of its travel to the other back and forth repeatedly at 300 ipm. Using the FRO start slow and increase until you find a speed that causes the problem. And since your hands are free, you can use a flashlight and find the issue. Reassembly points in the direction of the frame being physically out of square, not parallel or non-orthogonal.

From noise alone I would guess at one of the following:
Bad Servo Tune
Acceleration too high
Misaligned coupler or ball nut
Ballscrew whip
Y axis skewed
Some other physical bind

To add to what Gary said, because you can drive a machine at 600IPM does not mean it was designed to be run that fast. Ballscrew whip is a perfect example. Small diameter ballscrew being rotated at high speed will "whip" around when unsupported. Usually as the ballscrew nut approaches closer to the end of travel.

Seems like there is more of a goal in amazement as to how fast the rapids are in a machine as much as or moreso than the accuracy of the machine.

Slow it way down and see if the problem persists.

Marty

Guys,

I understand you point here. Speed is not the only goal here but I was finding it weird that this issue showed back up. The accuracy of the machine used to be good for the kind of project I do....

I will try setting up a program that moves the Y back and forth at various speed to see if I can associate the problem to speed. One thing I’ve noticed is that the clear path MSP showed a TrqSat error sometimes when the problem occur. The motors are plenty strong so I suspect I have some kind of misalignment that makes the motor work extra hard for no reason. Im picking up another laptop computer later so I’ll be able to see the status of both motors via the MSP as they run.

Have you physically removed the motors and moved the axis by hand? That would be my first step.

Sounds like ballscrew whip. Its not based on only going fast, it happens at a certain speed / resonance.

This is why many machines like yours will rather opt for fixed ballnuts or go for higher diameter ballscrews.

It could also be stick-slip. Is there contamination on your quide rails? You said it was taken apart and reassembled which could lead to contamination on the rails causing the carriage to stick in those areas.

I’ve inspected the machine a bit and I think I may have found the issue. I’ll confirm tomorrow but there seems to be a misalignment on the ballscrew. What really confuses me is that the machine was assembled that way but the issue showed up now.

I moved the axis by hand and there is no problem whatsoever. I’ve also done a test with my X axis and pushed it at 1000ipm just to see if I’d encounter some whip. To my surprise the X axis is able to do it without issue. The X and Y uses the exact same ballscrew and I’ll get the problem jogging at 300ipm on the Y axis. More to come on this...

Also, I found a weird and annoying behavior with the controller. If the master Y axis homes before the slave, it throws an error, which is fine. But when that happens, the controller erases the travel limits and sets them back to zero. Is this a bug?

See if you can recreate the issue. If so, explain the steps and post a fresh before report and a fresh after report. Thanks for taking th time to point it out.
Marty