Question re two-sided milling

Been engrossed in Fusion 360 lately trying to learn–so far good, though 3-D modeling and the software is a steep curve to get around. I’m now about ready to try to run a two-sided job and I’ve watched a bunch of videos, and some things have me stumped. I plan on using a “pin” or dowel method for indexing stock (and have a pretty good idea for that), understand how to do the setups for each side in Fusion CAM, but what is throwing me is the WSC setup and zeroing in CM once that is done and before the files are run. Bear with me for this rather long set of questions.

First, in most of the videos, the recommendation is to flip the z axis in the Fusion WCS when doing the setup for the second side so that Z is up as oriented to the stock’s backside. I get that part. But in a couple videos (here’s an example at about 12:30 in) the recommendation is to “pick up” the stock on the bottom in the CAM setup rather than the top (as was done on the top-side milling operation). Now, if one does that, this generates a series of questions for me on job setup and setting zero:

Should the Z zero be reset to the bottom (to the wasteboard) before running the back-side files? Or does one just flip the stock and leave the setup alone since Z was originally set to the stock top (which is now facing down) and the software knows top is now facing down?

Presuming Z is not reset (left alone from operation “A” side) and a face milling operation has been done (as was in this video), would that not necessitate a re-zeroing of Z since the stock would be thinner? Or is the software “smart enough” to know that a certain amount was taken off the face (which is now presumably sitting on the wasteboard?

My confusion is compounded by this video where at about 12 mins in he flips his stock, but does not re-zero Z (presumably because the stock thickness has not changed) and Z zero is in the same place for each side. In the CAM setup he picks up the WCS off the top of each side to be milled merely flipping the Z axis but leaving orientation to the top of the material.

Thanks in advance for any suggestions.

Here is an example for Fusion and shapeoko

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Thanks. The videos here show a technique similar to what I explain in the last paragraph–run side A, Flip on the pins, don’t re-zero. That one I get. What is puzzling me is the technique of setting up CAM to read side B off the bottom rather than top of the stock.

zero both sides on the bottom, i would not have one on top ant the other on the bottom

in fusion you can move the coodinate system to a new box point
Just select a new box point as shown here.

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there’s all sorts of ways to address this.

touching off the top on the first op is nice because you can effectively send a tool to the origin and not have to worry about it crashing into the part (typically if all is well - i usually add some z height and measure with a known block/shim thickness)

going off the bottom on the second op gives you a very solid known point. going off the top once flipped can vary depending on if everything in the first op was successful and nothing is out of the norm. sticking to the bottom, well, as long as the bottom didn’t go anywhere (shouldnt?!!?) you’re golden.

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I guess maybe I have stated my question in a confusing manner. The real crux of the matter is not where the WCS is set in the CAM setup. I understand that one can place it anywhere, as can be done in CC or any other CAM setup. What is puzzling me (go back and watch this video at about 12:50) is why would one switch the WCS to pick up from the top face of the workpiece on side A then flip the Z opposite and then pick up from what becomes the bottom when the piece is flipped. And, when this is done, how does one handle reprogramming Z zero (if at all)?

Touch off / probe the Z on the top of the material (machine side via CNCjs/CM). This becomes your WCS for the First Op (Setup 1) in the CAM program (Fusion/CC)
Run the program for Op/Setup 1.
Touch off / probe the Z on the bottom (machine side via CNCjs/CM ). This becomes your WCS for the Second Op (Setup 2) in the CAM program (Fusion/CC)
Flip the part over and run the program for Op/Setup 2
???
Profit