Fusion 360 depth of cut issue

I am having a problem cutting to the depth I want in one pass and am hoping I can get some help.

This is part of something larger I cut often out of 1/2" Baltic Birch (12mm) and what I want is to make my first cut with a 1/4" compression bit to a depth of 0.425". So that is what I have set as maximum roughing stepdown for the holes, slots, and outer profile. I have a final pass on the slots and outer profile with maximum set to 0.5" and taking the final few thousandths to clean up the cut.

When I run the file I can see in Mach4 that the initial cutting depth goes to 0.242" and this is about half the depth of the workpiece which I have set at 0.48". The BB I buy ranges from 0.46" to 0.485" but I zero off the spoilboard so the actual material thickness isn't that critical in this application.

The final pass where I cut the last few thousandths cuts like I want, the full depth of the work piece. And these are different profiles - the holes are 2D pocket, slots are 3D pocket, and the outer perimeter is 2D contour. The 2D contour has an option for even stepdowns and that is not selected. I don't see that option on the slots profile but I don’t want even stepdowns anyway.

What I have determined through trial and error is that I can set the max depth of cut to 0.380" and it works perfectly. If I set it to 0.385" and above then it cuts to the 0.242" mark. So somewhere between 0.380" and 0.385" is the tripping point.

Why doesn't the first pass cut 0.425" deep when that's the way I have it set and how can I fix this? It just seems like I should be able to set it to any depth I want, up to and including the full thickness of the workpiece, and my CNC should cut that without Fusion 360 overriding my setting in some fashion.

Files attached - screenshots and f3d files

Attachment 425078

Attachment 425080

Thanks, guys!
David

I looked at the first model, will look at the second one in a bit.

Since you are setting zero at your table (top of spoil board, I assume), I would recommend breaking your roughing pass into 2 parts (a separate process for roughing and finishing). If you want to stay... .050" off the bottom of the part for the roughing pass, set the "bottom height" at +.050", then just duplicate that pass and on the next one set the bottom height at zero.

I'll look at this more closely in a bit.

PM