Overcutting the roughing cut (negative machining allowance)?

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jamezwarner
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Overcutting the roughing cut (negative machining allowance)?

Post by jamezwarner »

I'm milling plugs from a lightweight foam, and I'd like to try using a foaming modelling paste to build up a heavier density surface layer after roughing, into which I can then mill a finishing cut in the dense layer

So what I need to do is a negative machining allowance (cut3d won't let me do it) to overcut the roughing cut in order to leave a certain thickness of paste after the finishing pass...

Other ideas
  • To trick cut3d into thinking it's using a smaller cutter, and rely on the difference - though this will only work for small differences... as otherwise my 1/2" cutter will need to make a crazy amount of passes (I run 40% stepover in rough)
    Set zero a lower X for the roughing cut, but this will only give me a layer difference in the X/Y and vertical sides will be exposed...


    Any ideas much appreciated...

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larrybadgett
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Re: Overcutting the roughing cut (negative machining allowance)?

Post by larrybadgett »

Lower Z zero, cut, apply material, go back to true z zero!
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jamezwarner
Posts: 8
Joined: Tue Apr 17, 2012 4:56 pm
Model of CNC Machine: Custom with Mach3 Controller

Re: Overcutting the roughing cut (negative machining allowance)?

Post by jamezwarner »

Thanks Larry - the issue with that is as attached, the sides of the cut expose the substrate...
Attachments
zissue.png

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rscrawford
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Re: Overcutting the roughing cut (negative machining allowance)?

Post by rscrawford »

set it up for a 1/4" bit with 80% stepover, but put a 1/2" bit into your spindle, and then lower the z 1/8". This will give you 1/8" overcut on horizontal and vertical planes.
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esteeme1
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Re: Overcutting the roughing cut (negative machining allowance)?

Post by esteeme1 »

James, Along the same lines as Russ......I would not try to use a standard size bit to calculate your tool path. If you're going to use a .5" endmill I would create a bit with a .4" diameter or what ever works to get the effect you need. Then you can adjust the Z depth as well I would use the same depth that corisponds to the radius difference. e.g. .05"
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