Pontiac and Rodney Gold,
Thank you for sharing your experience. I didn't realize the pointer wasn't going to be accurate enough. I'm not sure I follow 100% regarding the jig and the dowels though. The bolts and pins are mounted directly to the motorized laser table? Then the jig is bolted to the table when in use so when the board you want cut is inserted, it's perfectly aligned to the true machine 0,0 coordinate. Am I following?
Yep, that's exactly what I was trying to say. I'm not the best at explaining things in text sometimes!
The jig doesn't necessarily need to be bolted to the table. One good thing about lasers is there is no cutting pressure, nothing will push the jig while it's being used so you really don't need to bolt it down. The dowels in the table I mentioned are only to give you a solid, non moving, reference point to slide the jig against.
I see how that will register the first cut on the x and y but how does it help lining up the second cut? If the board isn't exactly square, it seems like like spinning the board around to cut the other side and using the jig wouldn't necessarily mean the cut will line up. I think this would be easier to show in a drawing. I'll follow up with illustrations.
Unless your board is 100% true a jig of that type won't work, just as you have said. In this case I would recommend using the jig for the first half of the engraving. After the engraving is done and before removing the part from the machine cut two holes with the laser.
Now, you need some way to find those holes after the part is flipped. This is where the spoil board comes into play. Set the spoil board up so it can't move, either with bolts or just "butted-up" against the permanent dowels at the edge of your table. (If it does move you can always push it back against the dowels.)
Cut two holes in the spoil board, exactly the same as the holes you cut earlier and use one of the two as your new zero. Now you can stick dowels in the spoil board holes, flip your part and locate it on the spoil board with the holes you cut in your first laser cutting/engraving operation.
Rodney, I found plenty of roller supports. Did you make your own rails?