One of my colleagues at work asked me if I could turn him some motorcycle engine valves on my Boxford. I said it was unlikely as the material was hard (he said he had a friend who could get him some square section) and from the finish I've seen on car ones they look precision ground. Any other thoughts on this?
VERY many years ago (I was still at school and used the school workshop so before 1966!) I turned down the heads of some motorcycle valves for a friend. He had sourced valve for a different bike with the same length and stem but oversized heads, which I turned down using brazed carbide tooling to fit his Panther 650 sloper. I don't recall it being too difficult
I use inconel exhaust valves as blanks, taking small cuts is quite easy with new sharp carbide, but I don't know how that would compare with whatever square section the chap can get.
The very top bits are hard - made of stellite - and the shafts can be hard chrome plated, but otherwise a valve isn't that hard to turn with carbide tools.
The valve shaft probably is precision ground though - the head can be ground into exact shape in the socket, so precise accuracy there is probably not essential, but getting the shaft right on a lathe might be a bit tricky.
Another potential problem I can see is going from square to round, carbide doesn't like that sort of interrupted cut, and you may have to use HSS and sharpen it a lot.