I'm making another thing to braze onto my Trek. This one is very high on the BQ koolaid scale.
"Broaching" the subject .... (bad machinist joke right?!)
Ahem. This is a broach. Basically a really hardcore saw or file, for cutting a square hole. You press it through a pre-existing hole and then add a shim. Eventually you come to have a large collection of shims, if you're wanting to square off the ends of a pocket made with a round endmill.
In this case, I'm making this square slot on the diagonal through a piece of stainless steel square bar. Can you guess what I'm making?
Think about what Jan Heine dreams about. Think Rebour drawing. Any guesses?