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varying Z measurements between areas of same height in model.

melfio

Plastic
Joined
Oct 2, 2020
I am machining plastic with a 10mm (0,39") ball nose endmill. I've used both morphed spiral passes and parallel passes to cut out a shape and I get varying heights on the top surface.

Where it says U the surface is higher, where it says N the surface is lower.

The upper part is made with spiral passes and the lower with parallel. The enlarged parts are of the spiral cut part.

The model for the CAM does not have these differences in height, and I can not see traces of this in the tool paths either. So I guess it is the machine. Any ideas what might be causing this?
 

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How much higher? What does the stock look like? How are you holding them?

Also why are you using two different toolpaths?
 
what is the machine?

Probably accel/decel issues, also lookahead could be an issue.

Please don't say this is a hobby machine.
 
What does the model of the part look like? Is it flat? Is the top meant to be dome shaped?

Plastic is highly unstable, have you verified that its not the material itself moving?

How tight or sloppy is the mill you are running this on?

If there is backlash, you won't get a good finish with a toolpath that has lots of small up/down z moves. A better strategy would be to machine by varying layer heights, this way only the x and y axis are moving simultaneously. z backlash is taken out of the equation, as it is only moving one direction and never moves while the cutter is engaged.
 
Did you try to make a wire from the CAD before doing the CAM? Not a programmer, just had my guys struggle with a couple bad CAD drawings over the years.
 








 
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