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Author Topic: toolpath occasionally, randomly goes in strange directions  (Read 4808 times)

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toolpath occasionally, randomly goes in strange directions
« on: March 16, 2010, 11:51:37 PM »
This problem used to be rare, but now it's quite frequent.  On my Sherline CNC (model 5200) machine running Mach3, the bit will be going along nicely, cutting a jewelry piece correctly, then, randomly, the tool goes way off path.  The X axis will overrun a few centimeters, then the tool will start going only in the Y direction for a centimeter, then it will head back on X in the other direction, all in the area of the wax it's not supposed to be touching.  I broke a bit recently because the bit was deep in the wax when the machine decided to go off path.  And it seems to go off path in the same way every time (though to different dimensions).  What made me finally brake down and post is that my tool ran into my four jaw chuck and kept trying to cut into it, causing lots of smoke and noise before I could hit stop.  I am not positive, but I believe my computer monitor wasn't reporting any problems.  As far as the computer was concerned, it was still cutting correctly and advancing along the G Code correctly.  No strange G code.  I usually run only new files, but this has happened to a file that I have run before.

Has anyone seen this problem before?  MikDundee on this post: http://www.machsupport.com/forum/index.php/topic,10879.0.html
seemed to have a similar problem, but no one seemed to solve his problem.

Any other details you guys want to know?

Thank you for your help.

Offline Hood

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Re: toolpath occasionally, randomly goes in strange directions
« Reply #1 on: March 17, 2010, 03:30:43 AM »
If the DROs report that the tool is where its meant to be then it is more likely to be a hardware issue caused by a motor stalling. If the DROs show the position of where the tool actually is then there is a problem with Mach.
Hood
Re: toolpath occasionally, randomly goes in strange directions
« Reply #2 on: March 18, 2010, 03:59:55 AM »
I really don't think it's the motors stalling.  The noise from the motors sounds normal when this happens.  Plus, it would have to be two motors (x,y) coincidentally going bad at the same time suddenly.

I was wondering if maybe my control box was sending the wrong signals to the motors?

Offline Hood

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Re: toolpath occasionally, randomly goes in strange directions
« Reply #3 on: March 18, 2010, 04:22:02 AM »
If the DROs dont show this wrong movement then I think it has to be outside of Mach that the problem lies as I believe the DROs represent exactly what has been monitored at the parallel port.
Next time it happens check the DROs and see what they say.

Hood
Re: toolpath occasionally, randomly goes in strange directions
« Reply #4 on: March 18, 2010, 11:20:45 PM »
Yes, I plan on it.  Thank you.

Now I'll just wait for my new pulley belt and bits to arrive so I can run the machine again.

Offline kf2qd

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Re: toolpath occasionally, randomly goes in strange directions
« Reply #5 on: April 09, 2010, 04:45:28 PM »
Is this happening when you use G41/G42? And are you using the Local System Rotated set to some value other than 0 Degrees?

Offline RICH

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Re: toolpath occasionally, randomly goes in strange directions
« Reply #6 on: April 10, 2010, 08:24:29 AM »
FWIW...... It could be a number of things, but if you are conservative in your velocity and acceleration settings you won't miss steps and have the axes go off in some wierd fashion.
RICH
Re: toolpath occasionally, randomly goes in strange directions
« Reply #7 on: April 10, 2010, 08:19:06 PM »
Some thoughts of something to check for.

1 )  have you moved any cables.  I had a long cable that was wrapped in a circle.  It produced a field that caused errant problems when my cordless mouse got too close to the cable.

2 ) Computer connected to the internet.  My shop computer communicates with the office computer and the internet via a home wi-fi.
I have to be careful that I disable the network before starting Mach.  Have had software updates come in unexpectedly while cutting parts.  That can cause some real  puckers.

3 ) Don't run a small shop vac near your motors!  You need not ask how I know.

Good luck with your projects.

Bob @ BobsShop