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Author Topic: What would make the size of holes change during cutting????  (Read 4144 times)

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LuLu

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What would make the size of holes change during cutting????
« on: December 02, 2010, 07:19:31 AM »
I have been having a problem with my CNC machine/program.  I am using a Vortech CNC, BobCad v21, and Mach 3.  I can be cutting out 10-15 tops that are correct.  Then the next top, the pocket holes are bigger.   What would make the size of the holes change?  No one has changed the program.  It just happens on its own.  I have asked several people, and no one knows the answer.

I would appreciate any help you could give.  Thanks!

Offline Tweakie.CNC

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Re: What would make the size of holes change during cutting????
« Reply #1 on: December 02, 2010, 08:02:57 AM »
LuLu,

How much bigger are we talking about and are the holes round ?

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

LuLu

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Re: What would make the size of holes change during cutting????
« Reply #2 on: December 02, 2010, 08:13:44 AM »
A strong 1/16 bigger.  And yes, the holes are round.  But they turn egg shaped when this happens. These pieces have to be exact each time.  

Offline Tweakie.CNC

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Re: What would make the size of holes change during cutting????
« Reply #3 on: December 02, 2010, 08:32:07 AM »
Hi LuLu,

The simple answer to oval holes is 'backlash' on the axis in the direction of the elongation. Check for loose parts, slipping couplers etc etc.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

LuLu

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Re: What would make the size of holes change during cutting????
« Reply #4 on: December 02, 2010, 08:40:24 AM »
Hi Tweakie,

The funny thing is, it only happens to 8 holes, the other 4 holes are fine.  All the holes are programmed the same, and they are the same size.   That is why I am stumped.  Why can it do so many tops right, then for a couple they are wrong, they the next few are right again??   Hmmmmm, I think our CNC is possessed, lol.  

LuLu

Offline Tweakie.CNC

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Re: What would make the size of holes change during cutting????
« Reply #5 on: December 02, 2010, 08:51:47 AM »
You could perhaps try positioning the work in a different place on the table and then observing the results.

Or possibly call an exorcist  ::)

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Graham Waterworth

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Re: What would make the size of holes change during cutting????
« Reply #6 on: December 02, 2010, 08:58:06 AM »
Could it be something as daft as a build up of dust in the belts?

Graham
Never give up, time will pass, the cloud will clear, the sun will shine once more.

LuLu

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Re: What would make the size of holes change during cutting????
« Reply #7 on: December 02, 2010, 08:59:46 AM »
You could perhaps try positioning the work in a different place on the table and then observing the results.

Or possibly call an exorcist  ::)

Tweakie.

Tweakie,

I did try a different part of the table.  Still had the same results.

I think it is time to call an exorcist.  ;)

Thanks for your help.

LuLu

LuLu

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Re: What would make the size of holes change during cutting????
« Reply #8 on: December 02, 2010, 09:02:27 AM »
Could it be something as daft as a build up of dust in the belts?

Graham


Graham,

That could be the case, but after cutting so many "bad" tops, it goes back to cutting "good" tops.

BTW, I am cutting solid surface.  If that makes any difference.

LuLu

LuLu

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Re: What would make the size of holes change during cutting????
« Reply #9 on: December 02, 2010, 09:14:59 AM »
I should add that I have been using the CNC machine and the same programs for 8 months with no problems.  This only started about a month ago. 

Someone suggested that maybe the person who wrote the programs, used a "floating code."   I have never heard of that.