Hole type flycutter drilling aid

Had to drill the holes for my boats gauges today. Turned out they were 83.5mm Diameter. Needless to say I did not have an 83.5 mm hole saw.
Best next to that was a fly cutter style hole saw I bought to cut holes in the ceilings for down lights. I could remember from using it the last time that the center hole (running a drill bit in it) wore out to the end and caused some damage. Solution a nice 2 x 4 screwed to the back where you want to drill the hole and the drill bit does not wear the 2 x 4 out as fast as the plasterboard.
How to apply this knowledge when drilling into a freshly manufactured center console of my boat.
Took a piece of scrap 6mm Ali plate, drilled the diameter of the drill to be used in the fly cutter and then using all the info from "how to punch right on the cross lines". I machines right up to one of the X axis and one of the Y axis, Then just 2 small holes to secure it to the center console and whalla:rocker:.
lined up the cut outs to the pencil lines and secured with the s small self tappers. Making the aid took about 2 hours but drilling the 2 holes no longer than 10 minutes and the gauges just propped in. Will keep this little aid for a next time.
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