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Cuts getting progressively deeper
« on: June 13, 2008, 06:23:17 PM »

I've done some searching, and mostly come up short here... hopefully this hasn't been beaten to death already.

I'm running Mach3 R 2.63 on a dedicated WinXP machine, and an AccuCut XP series router from Computerized Cutters.  The machine uses steppers.  Z axis is ball-screw, the others are rack and pinion, and it's pushing a 5hp Perske spindle.

I'm cutting 28 sets of lettering into a 2x4 piece of acrylic, and each set becomes progessively deeper.  There are 8 letters in each cut, so 8x28=224 movements up and down.  Initial cut height is .01, and by the end I'm probably cutting closer to .04 or .05.

I can only guess this is a lost steps issue?  I've brought my Z speed down to 20, acceleration is at 4 in/sec2.

I verified the G Code and every cut has a Z of .0100.

The manufacturer is closed until Monday, so any help would be greatly appreciated!!


Offline Hood

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Re: Cuts getting progressively deeper
« Reply #1 on: June 13, 2008, 06:37:25 PM »
Is it just the Z axis? Check the screws and slides to make sure there is no binding. Might even be worth swapping over motors and drives etc to see if the problem follows, just depends how desperate you are and whether it would void any waranty you may have on the machine.

Offline MarkC

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Re: Cuts getting progressively deeper
« Reply #2 on: June 13, 2008, 06:55:00 PM »
Sounds like it's loosing steps on the way up.
I'd drop the speed down to half or so and also drop the acceleration too, just to see what happens. It'll take longer to cut, but it might get you through this job til you can talk to the manufacturer

Just thought of this: check the coupler too

Re: Cuts getting progressively deeper
« Reply #3 on: June 13, 2008, 10:32:43 PM »
Thank you both for the replies.

I took the covers off, everything seems snug and connected.  I also checked everything for binding, greased it all just in case and checked it over - no problems found.  There is a manual knob to move the Z, and the axis moves freely.

I got my machinsts micrometer out and did some testing... it drifts at 1 in/min2 just as much as on 8 or 12.  After 40 up/down moves it's off by about .02.  The other axes (axises?) seem fine - all of my letters are evenly spaced and sized - I didn't put the micrometer on the others, but the calipers seem to indicate X and Y are fine...

I'm not up for swapping out motors this weekend, so I guess I'll just break it out into small runs an re-zero in between each set... AAAAARGH.  Sounds like this stepper might be shot?

Any other ideas, I'd love to hear them!

Thanks again,
Re: Cuts getting progressively deeper
« Reply #4 on: June 13, 2008, 11:05:04 PM »
Scratch my last post. 

I just re-ran a path over itself 3 times (5 sets of 8 letters in the path), and it's drifting on the X and Y as well.  Something isn't right, and I have no idea what... either way, it looks like no prodution for me this weekend.

Is there some other setting in Mach3 I need to be looking at??


Re: Cuts getting progressively deeper
« Reply #5 on: June 13, 2008, 11:07:58 PM »
There was another thread awhile back about a dude who was getting inconsistent cuts (sounds like your problem is repeatable though but WTH, I'll throw it out there anyway)  http://www.machsupport.com/forum/index.php/topic,6837.10.html

Basically Chip (He's really the master at this kind of problem) suggested using Sherline 1/2 Pulse mode.  It seemed to help out that dude- maybe it will help you too?

Re: Cuts getting progressively deeper
« Reply #6 on: June 13, 2008, 11:34:02 PM »
FIXED!  (I think...)

I only sort of understand what that setting means, but whatever it does, it works.  Just did 4 passes, depth and X/Y are dead on.

I did read that someone said it over rode the Step/Dir Pulse settings - the range listed is 0-5 and mine are set at 6?  No idea, just running the config the manufacturer includes... haven't really tweaked it any. 

This is a new machine for us (and I'm a noobie at CNC anyway) - I've been playing with it for a couple weeks building a prototype, but I was only cutting single parts.  Never really saw the issue until I went to cut a lot of them nested... 

Thank you all again, you saved a weekend of production time for us!!