MeshCAM not following geometry

Hey guys. Well, every time I start to think I’m ready to quit my day job and start machining full time another issue pops up. I have looked all over the forums here and on the Meshcam site but can not figure out where I’m going wrong. I am trying to work on a mold out of Renboard, and Meshcam is not following my geometery. This happens with both side A and B on the molds, two completely different files so its not a bad file. You can see in the pictures that the finish pass is “missing” on the ramps on both side of the mold, as well as on the sides of the center channel. For reference, the roughing pass only takes a brief trip down the center of the channel, and the pencil pass does it’s typical random dance around some corners.

Any idea? Thanks in advance.

How long are the flutes on your 0.016 ball endmill?

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I think you nailed it Justin, flutes on this one are 0.048". Makes sense.

Thanks man!

OK, so another question. I measured up my 0.016 BN and it will not work for the areas it’s missing for the reason JSmith pointed out. Even cheating it a bit, it will be closer than what I want to try.

I can change to a larger cutter for most of the mold, but need the 0.016" for the finer detailed areas. Do I run a second program and just machine isolated areas where the detail is needed? I have been working on removing and re-zeroing practice parts (extruded foam) but it still makes me nervous. Or is there a way to add an additional finishing pass with a smaller cutter? Yes I realize I do not need to remove the stock between cuts, just trying to prepare for the future if needed.

So I’m thinking I would need to go back and do something like this after the larger cutter does the heavy lifting? I know some of it will be wasted movements, but for now I’m OK with that.

I will point out that pencil finishing toolpath generation is really only effective with sharp inside corners. When I want to leave a small fillet, I’ll model the corners sharp and then pick a cutter whose ball-end radius will form the fillet.


Thanks Randy. Still wrapping my head around it. Do you run multiple programs on a single piece like I am suggesting, or do I have the wrong idea?

I run multiple programs on a single piece all the time. It is often the only way to get MesCAM to do what I need, especially in situations like yours, where multiple cutters will be needed to do specific areas of the workpiece.

Thank you Mr. Hume,

           I will be trying it this morning. I have been doing a lot of cuts on extruded foam to learn about the changes from my cutter path settings. Typically I will change settings 4-5 times, run through a simulation program, then once I'm happy with that, tackle the foam, then Renboard. Next week will be trying to run an 0.008" cutter through aluminum. That should be a good time...

+1 on the multiple programs on a workpiece. I try not to touch a finished surface with more than one operation, so I’ll use combinations of keep-in and keep-out areas, angle limits, etc. to tailor the machining.

But on your mold, Mark, it looks like you have things well in hand already.