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
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.
-- Peter Fairbrother
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