Re: ATM A-B-C Method for 90 Degree Corners

["Frank Ward" <thewards@mindspring.com>]

Richard, You said....

>The prisms may be needed for periscopes or gun sights to defend against,
hunt down, >and destroy the mutant ninjas.

But you also instructed:
Then clamp face C against face A and grind the two remaining feces on a flat
lap.

 Is this your second way to "destroy the mutant ninjas"? Sounds time
consuming.

Frank


----- Original Message -----
From: Richard
To: atm@shore.net
Sent: Monday, July 09, 2001 12:25 PM
Subject: ATM A-B-C Method for 90 Degree Corners


I believe that most of us are familiar with the A-B-C method for making
optical flats, but you can extend that method a bit to make fairly accurate
90 degree corners on prisms.

Start with three prisms that have one of the two 90 degree faces ground
flat.   Use a sharpie pen to mark these faces A, B, and C.

Clamp face A against face B, and grind the two remaining faces an a flat
lap.
Then clamp face B against face C and grind the two remaining faces on a flat
lap.
Then clamp face C against face A and grind the two remaining feces on a flat
lap.

Repeat this cycle several times, and you end up with a pretty darn good 90
degree corner.   I hardly see any light through a diemaker's square.  (OK,
OK, just a little bit of light...)

I have not seen this documented anywhere, but there it is one of those
processes like mirror grinding where the process itself creates the
accuracy.   That means you can do it on a desert island or after the final
near-extinction of humanity, mutation, apocalypse, and collapse of
civilization in you Idaho bomb shelter.  The prisms may be needed for
periscopes or gun sights to defend against, hunt down, and destroy the
mutant ninjas.

. . . Richard