2D and REST machining - why is this toolpath generated?

[BbellYS6XC]

The attached project is the finishing part of a raised-lettering scheme. The idea is to finish the surface with 0.02 corner radius bits - first 3/8", then 1/8". I don't want to touch the walls of the raised letter, so there is non-zero radial stock-to-leave. For the 1/8" bit, I turn on REST machining and increased the stock-to-leave to better illustrate the issue I'm seeing.

The intent is for the 1/8" to simply come back and clean out the corners that the 3/8" bit left behind. The problem is that instead of just doing the corners, it generates a complete contour of the shape. Most of that contour is spent cutting air. It's like the REST algorithm works for most of the pocket and then fails when it gets close to the shape.

I've tried other situations where it does what I expect and doesn't generate the full contour. It doesn't matter whether I use bull-nose bits or flat bits. The reason this matters is that for the actual part, the 1/8" bit has zero STL and it can create toolmarks on the floor. I increased the STL in the test just to eliminate possibilities and make the air cutting more obvious.

I've read some other posts that seem to be describing the same issue, but there is never really a resolution. In this thread, Seth Madore said he opened a ticket on this topic, but that was back in 2020 and there's no information about the outcome.

Am I just expecting too much of the 2D REST algorithm?

[HughesTooling · Accepted solution]

It looks like Fusion is not taking into account the radius on the finish tool. If you set the corner radius under Rest Machining to zero it works how you'd expect. Even setting the corner radius to 0.01 (under rest) it produces a complete a full pass, so it's not checking the selected cutter corner radius against what you set under rest machining! @seth.madore What do you think?

Mark

[BbellYS6XC]

Thanks!

[seth.madore]

@HughesTooling yes, it does look like something is going wrong. I'll look into this deeper and log a ticket when I get back from vacation.

[kieran.gill]

I've looked into it and agree, its not doing what I expect to unless setting the corer radius to be "0".

I've opened CAM-45210 to investigate and address this going forwards