This is part PSA and part request for supporting or refuting what I think is a bug. Here is a re-post of my report to AutoDesk:
I’ve reproduced what happened and think this is a bug that should be addressed. Here was my situation:
stock was already profiled to size using a 2d contour and I wanted to remove material from the back edge only
since my CNC was already zeroed to the original stock origin, I didn’t want to change this. However, the stock was originally centered in my setup, so reducing the overall dimension of my piece would have just re-recentered in the stock, removing half the delta from the front and back
so, I changed the setup to “offset from -y” which handily puts in the current offset into the field (which was accurate, as I hadn’t changed anything yet). I clicked OK, went back to Design and made my through-all cut to the back edge of the piece, went back to Manufacture and exported a path to re-contour (matching the edge on three sides and only material from the back)
instead it cut a crap ton off the front of my piece! I looked in setup to find that it did not honor the offset value, and upon adding my extruded cut, it auto-updated the value to re-center the part anyway
Here is a video reproduction of this bug.
At my bug report, I’m being told this is exactly as expected. Namely, if you change the stock mode for an axis to “offset from +/-” from the default “centered,” but you don’t explicitly enter a value (accepting the one that is automatically filled in), you should appreciate the feature that Fusion360 is still behaving as though it’s centered.
I’m biased as it semi-ruined some hard work as a result of this, but do think I’m objective when I say this is utter nonsense. Software should never look like one thing (you see the offset setting, you see an entered value) yet behave in two different ways depending on how you got there (it’s either actually offset, or potentially still auto-calculating a centered position).
Since I’m at a standstill, if you care enough and wish to support my case, I’d love a comment as I think this is a glaring flaw in the software and likely trivial to change. If you think the AutoDesk response is correct, I’d also love to hear your perspective!