edm or some parts are sintering in industry. it would be a complex broach as material intrudes on the bore - ie the opposite of say cutting a square hole where material is removed outside of the bore, but i suppose a broach could be made.
and bench work with a file as mentioned but this has the same challenge as a broach for this shape. fabrication is probably the easiest diy methods.
here's a shot of a D shaped hole i made via a fabrication. a cylinder was turn, part milled away, a chunk solder to it, returned to the lathe and final soldering into bore in the finished piece. P&S, or should that be POS camera would not focus where i want it to, but you get the idea
I also put up some shots of some homemade broaches, one hex and one square
PS, agree completely with miljnor, change the design for better functionality and easier production often makes a lot of sense and is a luxury of being a diy'r |