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Help with Random Problem
« on: August 06, 2009, 03:10:33 PM »
Hi All,

I'm looking for advice on a problem that I just cannot seem to sort out.

I have a 4x8 CNC router, running Mach3 (recent version), stepper motors, 3 axis, 5hp spindle.

Over the course of, say, 100 cuts, my Z axis is cutting progressively deeper.  About .040"  Travel up and down on each cut is .500"

Here's what's really stumping me:  

It started doing it all of a sudden - no changes to my setup, just randomly started one day.

We cut a lot of the same thing over and over, so these are not new programs.

I've tried to rule out every variable - I can run the program in the air with no problem.  I can run it in the air with the spindle and compressor running with no problem.  I've tried every combination of things on and off.  It only seems to do it when I have "real" material being cut.

My original suspicion was the parallel cable - I haven't replaced it, but I cannot seem to induce an error by moving it, etc.  It's not crossing or touching anything with current in it.

I upgraded Mach3 from an old 2.6x version hoping maybe new drivers would help - no change.

I've greased, checked and rechecked all of my mechanical movements - all is smooth, no binding.

So, that's it... I'm stumped.  Software?  Machine?  Angry ghost in my shop?  Any Mach3 settings I need to check?


Thanks!

Dave

Offline Chip

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Re: Help with Random Problem
« Reply #1 on: August 06, 2009, 03:19:39 PM »
Hi, Dave

First thing to try is reduce the Z axis Acceleration & Velocity values some in Config, Motor Tuning.

Chip
Re: Help with Random Problem
« Reply #2 on: August 06, 2009, 03:25:27 PM »
Hi, Dave

First thing to try is reduce the Z axis Acceleration & Velocity values some in Config, Motor Tuning.

Chip

Thanks for the idea Chip - I actually did that as well, cut it all the way in half.  Still the same result...

vmax549

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Re: Help with Random Problem
« Reply #3 on: August 06, 2009, 03:43:20 PM »
Check the polarity of the steps signals, some drive s are sensistive to this and can loose steps on reversals

Check the pulse time settings may need to go longer ,

Just a some thoughts.(;-) TP

Offline Chip

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Re: Help with Random Problem
« Reply #4 on: August 07, 2009, 03:02:07 AM »
Hi, Dave

TP is on the money it's the next 2 thing's I'd try.

If your using the same type drives, Your "Active low's/high's" should All be ether "Checked" or "X's" and use "Reversed" in Home's & Limit's to change axis Direction's if needed.

Use "Sherline 1/2 step mode" will give you the longest "40 us" Pulse's to test with, (It gives your drives a longer pulse to see the state of change.

Chip
Re: Help with Random Problem
« Reply #5 on: August 07, 2009, 07:40:00 PM »
Thanks for all the help.  After another day of fighting it, the problem answered itself - and it was nothing I suspected.

I was cutting some MDF this afternoon and the bit came out of the collet - twice.   I'd been cutting acrylic before that, and it was apparently only enough force to slide the bit down a little. 

Looks like a bad collet nut or a bad collet are to blame... replacements now on order!

Again... thank you.  This has been driving me nuts all week!

Dave