I broke a couple of very small endmills
cutting those ports. I had expected this: I
had gotten spares before starting the job.
The ends of the ports are not round and
aren't square either. Since they sit under
the edges of the valve, it doesn't matter:
port widths are critical to timing and steam
distribution, but the ends aren't.
The matte gray finish was left by lapping the
face on an iron lapping plate. They say that
that's a waste of time, because the valve and
face will wear in quickly whether or not
they've been lapped. It's probably true.
Those grooves out beyond the ports were
suggested to me by someone on the Model
Engineering mailing list, God bless'm. I was
close to putting the casting on the shaper
and lowering the entire face except for where
the valve actually rides. Lots of extra
work, and it would have changed the position
of the steam chest, leading to other
complications. The grooves were a simple
solution.
I don't know which way I'll do it on the
next engine. No problem with making a raised
valve seat, if one plans for it beforehand,
so maybe I'll go that route. Still, it's
extra work and probably isn't any more
effective than the way I've done it here.
