I actually just drilled the bottom piece. I think a bored hole would be better as you can control size more precisely and also ensure a round hole.
i formed bottom section first, acts like shell holder in ram. Cut roughly to length. Drill 3/3” then hole. Reverse part and use 3/8” endmill to get flat bottom center hole. Drill to required size for cutting disk. Then mark and cut slot.
i formed bottom section first, acts like shell holder in ram. Cut roughly to length. Drill 3/3” then hole. Reverse part and use 3/8” endmill to get flat bottom center hole. Drill to required size for cutting disk. Then mark and cut slot.