Ben Jackson wrote:
Ok, this is a stupid question, but are the inside faces of a
machinists
square supposed to be square, or only the outside faces? Or, put
another
way, are the blade and base faces both parallel?

I've got the old "never take two clocks to sea" problem -- I've got
two
squares and I piggyback them and I can see light between the blades.
So now I don't know which one is off...

--
Ben Jackson

http://www.ben.com/

If you've got a name brand square, the edges are supposed to be
parallel AND square with the world, that's why you pay the big bucks
these days for Starrett. There's a number of ways you can check them
out, drawing a line and flipping the square, then drawing another is a
crude way to do it, but effective. Most of the others involve surface
plates, sensitive indicators, surface gauges and/or check squares.
Lautard has a lot on squares in his books, one section details how to
lap a square for correction purposes, another section is about how to
make your own precision square. He also tells how to make a
cylindrical square.

Stan