Can someone show me how to machine this STL using MeshCAM?

This is one of those times where I hate MeshCAM. Such a simple task and I can’t make it do it no matter what I try…

I start with the attached STL. I’ll attach some renderings for reference.

I’ve already machined the outer edges which worked fine. Now I want to machine the slot in the center (only)… but MeshCAM simply will not do it. I want to use a 1/8" endmill. The slot is 0.130 wide. You can see that I’ve defined the zone to machine. It no workie. As you can see, MeshCAM just tries to peck at it 1000x which won’t work.

ENTRY DUCT.stl (100.5 KB)

That is a very small margin (.130" slot vs. .125" cutter) for MeshCAM’s toolpath calculation. See my post Roughing toolpath doesn't cover all of geometry? for my thought-model of what is going on. In this case, the “machining margin” is the .0025" difference per side between the groove and cutter. Your best chance (other than using a .094" cutter, which would be easy peasy) is to use a .0001" calculation tolerance. If MC still can’t calculate a clean toolpath, you’ll need to use a smaller cutter.

UPDATE: here is my trial. First the parameters

And the toolpath which is pretty complete without many lifts

After looking at your STL, another factor might be “pinch points” where the facets along one wall of the trench aren’t coordinated with the facets on the opposite wall. If you can export a finer STL you might also try that.

Also, by selecting Machine geometry only and a Machining Margin of 0, you don’t need to define a machine region since MeshCAM won’t take the cutter centerline outside the geometry boundary so it won’t try doing the perimeter.


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Thank you very much, @Randy!

Thanks again, @Randy. It didn’t cut the whole slot but that was easy to clean up. I appreciate the help.

You’re very welcome, @Tshulthise.