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Author Topic: Strange Dropping of Z  (Read 3341 times)

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Offline maxy

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Strange Dropping of Z
« on: May 04, 2008, 06:40:43 PM »
Hi everyone,

The problem, when im cutting the Z keeps dropping down a bit at a time....We are cutting only .200 into the MDF so thats like nothing for the 10hp motor...as far as pull goes....I have figured out when it's happening, I'am running a  3/8ths bit (ball nose) and when it gets into a corner it causes a vibration or chatter which makes the Z drop by 3-5 thousands. So each time the bit hits the corners it drops another 3-5 thou...and by the time it's finished the part .....it may have dropped an inch.

The Z DRO does not show the dropping which is strange i had to manually attach a digital readout to the Z to see where the drops occurred and i could see the drops showing on the digital scale i attached, but the Mach Dros did not show it dropping at all.

I have changed my Encoder with a new one and it still does it, we have also set the stiffness in the skyco controller card to the max as we thought it may have been the problem...but it seems not to be.

So now im totaly lost as how to fix this crazy problem.

Someone told me mach does not handle large files well...could this be the problem as the CPU is not keeping up ??? the file is about 10 megs.

Someone must know the secret.....thanks in advance

Jmaxy >:(
« Last Edit: May 04, 2008, 09:43:47 PM by maxy »

Offline Hood

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Re: Strange Dropping of Z
« Reply #1 on: May 04, 2008, 07:22:13 PM »
Dont think this is a Mach problem, sounds more like hardware. Sounds like your cutter when getting to the corner is pulling the axis down into the work with the extra grip its taking.
 Can you adjust the following error on your servo drive? if so set it smaller and see if it trips out in the corner, this will let you know for sure its your motor getting hauled down by the cutter in the work. You could try taking lighter cuts and that should help.

Never heard of a problem with large files except if your graphics card isnt up to it then the toolpath can take too much to draw, shutting off the toolpath or getting a better card solves that problem. One way to check if file size is a problem is just use part of the file and run it and see if its still getting problems at the same point.

Offline maxy

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Re: Strange Dropping of Z
« Reply #2 on: May 04, 2008, 09:46:10 PM »
Hi Hood,

We are just cutting into MDF and the cuts are .200 deep which is nothing for our CNC...we are running a 10hp motor....i have noticed that the vibration causes the dropping...like it's somehow affecting the encoder ?? maybe.


Offline Chaoticone

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Re: Strange Dropping of Z
« Reply #3 on: May 04, 2008, 09:54:33 PM »
Maxy, do you have pics of where you had your scales reading the movoment? It could be your coupling on the z screw, bit pulling out of the collet, ect.,ect.

If mach isn't showing a change in the DRO I doubt it has anything to do with it. I think it is purely mechanical.

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