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Author Topic: Pocketing and Island avoidance issue, need help  (Read 14998 times)

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Offline 2bits

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Pocketing and Island avoidance issue, need help
« on: April 18, 2009, 09:56:53 PM »
Newbie using a home 'desktop' cnc.  I've been at it hard for close to 2 months now and have been getting more advanced with some projects.  This led me to my current problem and the software vendor says it's not their problem.  I can cut Left, Right, on the line of circles, squares, whatever without issue and within a .002 tolerance all day long except for Pocketing with Island avoidance.  In fact, take a simple 1" circle, put a .175 circle in the middle of that and tell it to pocket it and avoid the inner circle and I end up with .150 - .155, yet the outside of the pocket is 1.003  I can separately cut a .175 circle and be within .003

I have calibrated the system on X and Y it's within .001 - .002 (dialed in a 4" block measured at 4.279" and got 4.278"), backlash is the same, I can cut a 1" circle and measure all the way around and get 1.006 - 1.007.  I've replaced the router with a better one and verified I do not have a runout issue with either the router or the bit.  Again, this only happens on islands within pockets.  My current workaround is to cut the raised island first with a slightly larger toolpath around it, then pocket specifying the larger toolpath for island avoidance to prevent it from getting whacked.  If I do this same procedure without the larger toolpath, it will get cut down.

Anybody know why this is happening?  Is it some configuration issue between the post processor and Mach3, or some setting in Mach 3?  I'm new at gcode, but the simulation looks correct and the gcode looks correct, yet, it will eat into the island.

Appreciate any help on this.
Thanks,
Mark

Offline Hood

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Re: Pocketing and Island avoidance issue, need help
« Reply #1 on: April 19, 2009, 05:08:26 AM »
Maybe if you attach your code someone will see if there is a problem with it.
Hood

Offline 2bits

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Re: Pocketing and Island avoidance issue, need help
« Reply #2 on: April 19, 2009, 10:19:04 AM »
Gcode file attached.  Thanks

I should mention that I have tried this cutting with climb and conventional cutting and a finish pass with no difference in the outcome.
« Last Edit: April 19, 2009, 10:30:26 AM by 2bits »

Offline Graham Waterworth

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Re: Pocketing and Island avoidance issue, need help
« Reply #3 on: April 19, 2009, 01:35:06 PM »
Try this g-code, it pockets a .175 island in a 1" dia

See if it makes things the correct size.  Your sample code was cutting octagons not circles, was it meant to be like that.

Graham.
Without engineers the world stops

Offline 2bits

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Re: Pocketing and Island avoidance issue, need help
« Reply #4 on: April 19, 2009, 04:47:11 PM »
With so many files and trials going back and forth, that may have been the gcode tech support sent me to try, just in case, I regen'd the gcode from my file, like yours a 1" hole with a .175" center.

I'm afraid I'm really new and green at this and just starting to read and understand the gcode, but I have noticed there have been a couple differences in how I've seen 'circles' handled from a friend of mine (green like me) and tech support and the software itself.  Octagons doesn't sound right, but I couldn't tell why it is.

I ran your gcode and ended up with .165-.168 measuring around the island, the outside of the pocket came in at .999

Thanks for looking at this,
Mark

Offline Graham Waterworth

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Re: Pocketing and Island avoidance issue, need help
« Reply #5 on: April 19, 2009, 05:58:18 PM »
what material are you cutting?

Graham
Without engineers the world stops

Offline 2bits

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Re: Pocketing and Island avoidance issue, need help
« Reply #6 on: April 19, 2009, 06:04:36 PM »
Cast Acrylic .250 and .125 thick

Offline Graham Waterworth

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Re: Pocketing and Island avoidance issue, need help
« Reply #7 on: April 19, 2009, 06:08:07 PM »
How much of the tool is sticking out of the collet/chuck, rule of thumb is 5 times dia max.

Graham
Without engineers the world stops

Offline 2bits

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Re: Pocketing and Island avoidance issue, need help
« Reply #8 on: April 19, 2009, 06:13:10 PM »
The bits have rings on them, I put them to the ring.  .8" from the top of the ring to the end of the bit

Offline Graham Waterworth

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Re: Pocketing and Island avoidance issue, need help
« Reply #9 on: April 19, 2009, 06:25:10 PM »
I can only think its cutter rub that is causing the difference in size, have you tried running the feed and speed at a much higher rate?

Graham


Without engineers the world stops