• Cut out the main board.

I worried for a long time about this, and did lots of test cuts and preparation. It was the only nice piece of plywood for a reasonable price I could fit in my car. If I ruined it I'd have to spend more time and money getting a new bit. Stakes were high. My woodshopping table had a bend in it, so I belted it with a hammer for a bit until it was flattish, I then laid some particle board offcuts over it as as buffer.

Marvellous! Nice sharp edges, no wonky bits. Two minor burn marks where I had to stop and change arm positions, but they will sand out easily. I exposed three minor voids in the edge as I was cutting. I haven't quite worked out what to do with them. I might fill them with sawdust and PVA glue, or I might rout the circle down a little smaller and put oak banding on this part too. That would look nice, but it would mean buying more wood.

I gave the circle a light sand with some 180 grit sandpaper and a cork sanding block. I could feel no irregularities in the surface at all. It was all very nicely smooth. I went over it again with some 240 grit to remove the marks from the 180 grit. I also sanded around the edge, being very careful not to create any flat spots. Some parts had some fuzzy burrs leftover from the routing, but they fell away with light sanding.

I came back to my workshop a few hours later to put another coat of varnish on a test piece, when I noticed that the antlions under my workbench had cleared the sawdust out of their holes. Very cool.

• Varnish a piece of scrap ply and sand it, then varnish it, then sand it…
• Work out how to mark the lines on the board.