I saw this method used with a tool changing system I saw at Mr. Forney's shop a while back. How many people have mounted a secondary zeroing plate on their machine? Instead of pulling out the zero plate and zeroing to the table surface every time (which may become warped or otherwise unlevel over time), you could zero to that plate using a custom routine which is already perfectly calibrated to the table surface?
Assuming you mounted it correctly, you could use that point in a zeroing routine which would zero the machine to where the spoilboard surface *should* be, regardless of any minor imperfections the surface has, which may otherwise throw off a normal zero plate by even .01" in certain locations.
The only problem that could occur is that since the machine is zeroing to the exact same point every time on that secondary plate, it could cause a little pock mark/impact point of you zero V bits on it too many times. That could be fixed by making the software pick a random point within the area of that zero plate, assuming you can ensure the surface of it is completely level to the table. You could solve that by initially planing down the surface of the plate with the cnc after mounting it (assuming it's made of something soft, like aluminum/copper/brass/etc), so you can guarantee that the plate/spoilboard/machine is all completely aligned together.
Has anyone had any experience with this? Is it worth the setup time for such a simple modification, or has it seemed to help with accuracy/consistency?