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If your pcb's are always the same dimensions, you can add vacuum to the hdpe (or delrin) holder, that way you do not need the screws and the vacuum overcomes any board warping. No need to resurface your jig.
I have used this setup for years without failures.
On Feb 10, 2020, at 11:05 AM, "John Ferguson via Groups.Io" <aol.com
Maybe there should be a subject change. Have a look at the two fixtures
whose photos I've attached.
I make printed circuits which are about 2 inch by 3 inch. I found that I
couldn't get reliable trace widths unless the board was absolutely level
to the machine. So I started with an MDF fixture bolted to the milling
table and drilled and tapped in four places so I could use nylon screws
to hold the pcb down. Every time I do a new setup, I mill the surface of
the fixture with a fly-cutter to level it. This works 100% of the
time. I've had no bad experience with PCB's not being of constant
I had such good luck with the MDF board that I made a better one for
HDPE. I also made a jig to drill the holes in the pcb so they would be
sure to align with the ones in the fixture.
Frankly, I don't see how you could ever get reliable cuts without
leveling the surface the pcb is secured to while etching.