Z changing somewhere/somehow during cut

Had something odd happen last night where the z-zero changed somehow during the cut.

I have a sbp file (part I drew in Fusion360 and wrote out using the HB post processor). When I was using the 1/4" spiral upcut bit it was cutting through the material but when I switched to a straight flute 1/4" bit an ran the same file it did not cut through the material. I did re-zero out the top after the bit change and verified that both a setting of Z=0.75" was 0.75" above the surface and then Z=0 was just touching the surface.

The chucked bits the spiral upcut is about 0.25" longer than the other and it is also possible the sprial upcut is changing zero as well just not as noticeable (never checked it because it was doing what I needed).

Tested and reset it many times assuming that I didn't zero it or was user error. Always the same result (z-zero is higher after the cut).

I am going to simplify it tonight for testing and have it drill a simple hole and see if that works. But figured I would ask in case anyone knows what is going on.

The most common cause of z-zero inaccuracy is running out of travel either at the top of bottom of the Z axis. Topping out will shift the Z Zero down and cause the bit to cut too deeply. Bottoming out will shift the Z Zero up and cause the bit to cut above the material. How deep is your cut? Maybe if you slide the router down a bit farther in the bracket when using the shorter bit? Though there are definitely other things that might be causing this--but good to rule out the easy ones first.

Brian

Yup 100% z travel problem. Once I moved the router down worked as expected.

Then it dawned on me that a “verify” button on the job run would be very useful. The preview knows all of the x,y, and z coordinates from the file so that could check against the bit offset and give me a green go or red stop.

Yea-- What I'd really like is automated limit checking--once you home the tool, we know exactly where your hard limits are--and should be able to predict if the tool will hit one during cutting...this is on my wishlist for future software releases.