Tonight I thought I would show how I do the indexing.
In Fusion 360 I set up four solids which divide each sheet into four work areas. Each solid is 780mm wide and 600 mm deep.
Then I set up the cutting operations for the whole sheet BUT THEN, when generating a cutting operation I tell F360 to keep it within one of the work areas. I do that four times per sheet and end up with four cutting operations.
The next crucial step is to accurately move the sheet by 600 mm between operations. The sheet slides forwards and backwards on the special clamps I mentioned in the first post so it's always in the same position in the x axis, here is how I do the y movement.
First thing to keep in mind is that I use the homing position as the zero point, so I don't have to worry about power failures of canceled operation stuffing me up.
So when first started the machine homes and I set that position as the zero point. Then I move the tool down to the work surface and set the Z zero.
Then I send 's300' and 'm3' to turn on the spindle, quickly jog down to z-1 and then back up to z0. That leaves a little hole at the home position, which is also 0,0.
Then I jog y by 600 and now the tool is where the hole I just made needs to be!
Then I loosen the screws holding down the ply sheet, slide the ply sheet so that the hole is under the tool bit and then tighten down the screws again ready for the next cutting operation to be started.