Mill Steppers Locking Up, Help.

[Cartierusm]

OK, so I've posted this question on Mach's forum as I originally thought it might be an electronic problem, but I'm not sure if it is anymore as I think I've tried everything. Basically, I have a Bridgeport that I converted to full CNC, it's been working for a year now and works awesome, there's only one problem. If I make certain moves it locks up, I think the, Y axis, if I go over 20 IPM rapids, it doen't happen all the time see below for symptoms.

My system, 1200 oz.in Steppers on all 3 axis', 72 VDC PS, Keling 8078 Drivers. The steppers are direct drive to brand new ballscrews.

The problem appears when doing rapids where one move is shallow and one is long, such as: Let's say start at X0 Y0 and move to X10 Y.1, then the axis's lock up.

I originally thought it was an electronic problem as I can run each axis at 150 IPM with me pulling on it and it drags me and doesn't lose a step. So I tried grounding everything, then changing the pulse width and a whole host of other things to no avail.

If I run at no higher than 10 IPM full blown cutting I have no problem.

So if anyone has any suggestions on what to tweak, change or fix or any ideas on what can be going on I'd appreciate it.

One idea Himykabibble had was check the power supply with a scope as all axis are moving and see if there is voltage drop off, or something like that, but I don't have a scope, but I could borrow one, but no idea how to use or what to look for.

I could remake the housings and make it belt drive to get more torque but not sure what the top IPM would be.

Bascially it's either an electrical problem or a mechanical. If it's mechanical then it's probably one of the axis's binding, but if I can run at 150 IPM and having nothing happen is it just the mass of two axis moving at the same time, because it doesn't happen when making large exaggerated moves, just when it's making a long shallow taper move.

Thanks in advance, as I love my CNC and works perfect but keeping it at 10 IPM gets irritating as I could be cutting at 40 IPM!

[Cartierusm]

Here's a thought, I was just reading another post...Anyway, when I set up steppers I go by the sound as indicated in the Mach3 manual. I set the acceleration so it starts and stops smoothly, but not abruptly. Now during the testing to see if I could get the problem to go away I, of course, tried different accel and velocity settings. What if I set the acceleration REAL low where it make that winding up sound, what would that do during machining, would it mess up the timing?

[H500]

It sounds like you have a resonance problem. Try accelerating very slowly and listen to the sound of the motor. At the resonance speed, the motor will sound noisy and then quiet down as your speed goes up.

If that is your problem, the simplest solution is to build some dampers for your motors. There's a thread on how to do this.

[H500]

This is the thread. If the link don't work, copy and paste it into your browser.

http://www.cnczone.com/forums/showthread.php?t=32284

[Cartierusm]

Thanks for the suggestion, but the axis that has the very small move is the one that locks up not the one making huge moves. So does dampening come into effect when an axis is moving real slow?

Like today for example I had to move from X7 Y.005 to X0 Y0 and the Y axis locked up because of the shallow move it had to make because mach makes the move go at a diagnoal as it heads toward it's destination.

Could it be a problem with the microstepping feature, I have it set to 10x microstepping.

[H500]

Microstepping won't cause problems. The motor will stall when you run at the resonant frequency. This occurs when the motor is spinning relatively slowly. Did you do the test I suggested?

[Cartierusm]

No, I didn't but I did read the thread, very interesting, sounds like it could be my problem. Could you explain how to do your test, such as should I be adjusting the speeds in motor tuning or use the jog speed in mach?

[coop2005]

i have seen this same problem, what cpu speed are you using. I had to turn off enhanced pulsing in mach3 and this removed this same issue; however, that is just masking my problem and the real problem is my 1ghz cpu is not fast enough.

[H500]

Cartierusm, if you set the accelleration in Mach3 to something very low, the motor will speed up very slowly. When it reach the resonant frequency, the motor will be noticeably noisier and might even stall.