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Author Topic: A question about unexpected and unwanted plunge moves.  (Read 380 times)
Imagining
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« on: September 28, 2011, 18:43:38 pm »

A question about unexpected and unwanted plunge moves.

What is being machined is wood to make a piece of molding that will be cut into two pieces, and then trimmed and fitted to a piece of furniture.

The height [distance along Y-axis] is not a concern as the material, wood, is precut the appropriate height.  The depth [distance along Z-axis] is not a concern as that is what is being machined.   The width [distance along X-axis] is not a concern as the cuts made on the table saw will be perpendicular to CNC machines X-axis.  The entire piece is not being machined by the CNC as the places where the pieces have to fit are not the same size and not exactly the same shape.  [Chisels and planes will be used for the final fitting!!  Hand tools still have a place in furniture making.]

The primary problem is this:  Along the X-axis, the Cam Bam generated g-code has several unexpected plunge moves that are not productive or wanted.  The original CAD file [SketchUp] was carefully checked for hidden geometry, of which none was found.

The secondary problem, which appears to be related, is:  This piece is cut out of wood and is a molding.  The plunge moves at the ends are not productive as two pieces will be cut from this piece so having the machining include these plunge moves is not necessary.

Is there some way to accomplish the remove of both of these?

STL, CB, and g-code files are attached.

Post Script: I have read about Clip Areas and Boundary Shape IDís, however, what is appropriate and SAFE to use eludes me.   [If its not understood, its not safe!]


* leg blank for small dresser valet_001.stl (33.36 KB - downloaded 33 times.)
* leg blank for small dresser valet_001.cb (28.01 KB - downloaded 31 times.)
* leg blank for small dresser valet_001.Part1 [3DSurface1].nc (12.33 KB - downloaded 30 times.)
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10bulls
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« Reply #1 on: September 28, 2011, 19:57:46 pm »

This seems to be a side effect of your model height (2.5) being an exact multiple of passes given your stepover of 0.5 and tool diameter of 0.25.

This results in toolpaths that just skim the model side and I suspect it is very tiny rounding errors that are making it flip from 'hitting the model', to 'not hitting the model' and hence the sudden plunges.

The easiest way to avoid this would be to change the stepover slightly, so you don't get an exact number of passes.
Changing the stepover to 0.49 will avoid the sudden plunges as the tool path will then be more decisively inside or outside the shape.

I will make a note to investigate ways of detecting or avoiding these rapid finishing plunges.
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Imagining
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« Reply #2 on: September 28, 2011, 21:40:53 pm »

You are the best!!!

That is about the most esoteric thing I've heard of in a long time.  From now on if I get odd moves, just change by 1/100-inch.  Cool!!

Plunge moves along X-axis are gone; used 0.48 as step over.

Why are there still the plunge moves on each end?

I can live with those, but just wondering.
« Last Edit: September 28, 2011, 21:45:27 pm by Imagining » Logged
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