>>>>> On Thu, 07 May 92 13:49:53 PDT, Captain Capsaicine <sfisher@wsl.dec.com>
>said:
Captain> ... in the days of the
Captain> T Series recommended smearing the top of the block with valve lapping
Captain> compound, dropping the head on it, and carefully moving it in smooth
Captain> circles so that you got the two surfaces perfectly flat with respect
Captain> to one another. Then you don't use ANY gasket.
One trouble with this, as I rememeber from my telescope-making days, is
that you DON'T get a flat surface this way, you get a spherical one.
That's how you make a spherical telescope mirror -- grinding the
mirror blank against a "tool", usually another piece of glass.
To ensure you control the focal length of your mirror, once you achieve
the curve you want you start swapping the tool and blank so as to
avoid dishing out any more. It seems that the pressure as the tool
overhangs the blank makes it dish out.
This is, um, rather impractical for a block + head. I'm not sure the
effect would actually be noticable on these great pieces of cast iron
anyway, but it's fun to empty out the trivia room in my brain every
once in a while.
The sphere is the one surface that can slide against a mating surface
in all directions, and a plane is a degenerate case.
But we knew LBC lovers were degnerate anyway.
--berry
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