Why does Z height in CM not represent accurately on the first stepdown?

Hi this “issue” has been bugging me consistently since I started to pay attention to it. Sometimes on a job I’ll set multiple stepdown depths (in Fusion 360) at say -1.25mm each stepdown.

Then I’ll set zero in CM and start the job. Then while watching the job in CM i’ll notice the Z height equals -.75mm on the first pass then on the next pass it’ll be -2.00mm (2-1.25mm = .75mm).

So my question is why is the first pass .75mm and not -1.25mm?


1001.nc (31.5 KB)

ncviewer confirms the first pass is at -0.75mm

And the second at -2mm

So…it must be something in the CAM, can you share the F360 file ? (maybe not, Fusion360 being down and all…)

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@Julien working fine for me!
https://a360.co/3mmhGUR

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The total depth is 7mm, stepdown 1.25mm, it takes 5.6 passes, and I guess…it just chooses to do the odd 0.6 pass first instead of last:

This is a facing Op, and interestingly, for a pocketing Op it does what one would expect, do the shallower pass last:

image

As to WHY a facing op with multiple depths is managed differently…I have no idea.

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Thank you. That’s been bugging me alot. It’s also really annoying.

Isn’t there a checkbox for “use equal step downs” or something of the like?

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Ha, it seems like there IS an option for that

http://cadcamlessons.com/multiple-depths-fusion-360-2d-contour/

Maybe not for facing Ops, I did not check. Sometimes options come and go depending on the type of toolpaths.

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Unfortunately, I cannot typically surface the materials I work with, so outside of my fixtures, it is an unused operation. But surfacing has the same option. I think of step down setting as being a max allowable, this can be augmented by specifying the number of stepdowns, and the even stepdown option. I use these on materials that do now allow post processing, like HDPE, to disguise my machines resolution and rigidity.

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