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Author Topic: Very odd !!! Multi pass holes are stepped  (Read 1713 times)

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Very odd !!! Multi pass holes are stepped
« on: May 17, 2016, 07:59:57 AM »
When cutting some holes for a bearing in 16mm aluminium the sides have a tiny step from pass to pass. It is not a step in the manner of position changing. The hole diameter reduces.
The job was set up with 3mm deep cuts so 5 passes leaving 1mm bottom.
The first pass produces a hole of the correct diameter then the next is a tiny amount smaller. Just enough to detect with a fingernail. Each subsequent pass gets smaller and smaller. After 5 passes the bottom is about .1mm too small. Not a lot but the bearing won't go to the bottom and don't like just increasing the hole size till it does.
This is  very repeatable and a shallower job with less passes has a smaller difference top to bottom, fairly consistent step size.
I was originally using a 6mm 2 flute and when seeing problem thought tool deflection so went to 12mm 2 flute. No difference !!!

I have been scratching my head trying to think of a possible cause.
This is a servo based machine and returns very accurately to the home position so i tend to rule out missing steps.
The file was generated in Aspire 8.

Looking for some help with my head scratching and if anybody has any ideas they would be most appreciated.


Offline Tweakie.CNC

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Re: Very odd !!! Multi pass holes are stepped
« Reply #1 on: May 17, 2016, 08:15:02 AM »
Just a thought but check your Aspire generated Gcode -  if each subsequent pass uses identical Code (excepting the Z position) then it is likely to be a mechanical issue with your machine.

Re: Very odd !!! Multi pass holes are stepped
« Reply #2 on: May 17, 2016, 10:41:54 AM »
I was thinking after i posted that i should really check through that.

I don't have it here so tomorrow for that task.
Will spend some time with it and report back.

Re: Very odd !!! Multi pass holes are stepped
« Reply #3 on: May 21, 2016, 10:33:26 PM »
Checked and aspire is correct.
Am starting to think it is play in the temporary belt drives.
Am cutting new drives from ally, which is why the stress over bearing fit.
Can get around the problem with a full depth pass to clean up. Will do that and finish the new drives and then see what we get with them installed.
Thanks for your thoughts