I had to do some manual internal screw cutting today as the job was too large to go in the 15 L spindle. It was 40mm 316 stainless and had to be drilled and bored to suit a 1.25inch UNF thread. The people I’m doing it for gave me a spiral tap to use? Of course I had no hope of turning that in there, so I decided to screw cut, it chipped a few tips so I ended up finishing off with good old HSS. Any recommendations for a tool and tips that would do the job without breaking?
Yuk. Thread mill? Minor diameter would have to be spot on i would think. Matched to the tap tolerance. Tons of lube. Work hardening is your enemy. Starting after stopping, you hit hard. Have tapped invar before, tapered pipe threads. No damn fun.