You guys might want to use the self adhesive sandpaper on the end of the mandrel method.
(as seen in the Tree Monkey video. Is it still out there somewhere?).
The sandpaper on a flat mandrel/arbor end doesn't track the undulations of the combustion chamber the way a single point cutter does.
Take a sheet and apply it to the end of the mandrel and then carefully trim it to be the same size as the mandrel.
No wadded up bits or dingle berries hanging over the sides.
They can scratch the cylinder bore walls as you insert or remove the tool.
The sandpaper needs to be flat with no big wrinkles or lumps, EVERY time you mount a piece.
You need to make sure there are no limps of crud old paper or glue on the mandrel each time you swap the sandpaper.
A high spot created by any lump underneath the sandpaper will still track the existing variations of the squish band and basically repeat them.
View attachment 286996
I was inspired by
@Moparmyway to try a diagonal squish band. The theory (for me at least) is that it adds a larger surface area for the explosion to push down on the piston. It’s hard to see in the photo, but there is a band cut at a 30degree angle on the outside of the piston crown. Sort of a hybrid of a popup and a dome piston.
View attachment 286995
This is the mandrel I hacked up to cut the squish in the jug. The cutter is a piece of HSS ground to a 30 degree angle. I used the same bit on the lathe to cut the piston so they match.
As for the "Turbo-Crank" weights?
I think that I'd want to run a rotating tool across the cuts so as to not leave all of the stress raisers of filling~cutting across (side to side) the weights.
Any marks left should be in the direction like they would be wrapped around the weights, Not Across them.
Same issue with opening the holes in the side of a piston. Need to not leave the scratches, sanding, polishing marks going across the walls.
Always want to have them following the wall. Ala rotary tool marks or spinny~twisty sanding by hand.
All that said....You guys are still having more fun than me!