"CW" wrote:

If the angle it forms with the rule is not square, return it or
throw it away. If I were in your position, I would buy a GOOD
combination square a they are very versatile. You won't find a good
one at Home Depot. I would suggest Starrett (though I have a
Mititoyo). There are several top end combo squares that are as
accurate as a Starrett but Starrett will, at a very reasonable
charge, fix it if you damage it. Expect to pay $75 to $100 for it.
Seems expensive but well worth it. The cheap ones that you find at
your local home center are near useless. When setting up a machine,
you need accuracy. If the machine is not set up right, it will
transfer this inaccuracy to the work piece. After making many
pieces, all the errors will ad up to the point things won't fit.
This is particularly bad for the less experienced as they may not
know what the problem is, They will likely think it is something
they're doing wrong when it really is a badly set up machine. You
often here people say within 1/64 is close enough for woodwork. For
some things it is but for many things, 1/64 off might as well be a
mile.

Just curious.

Since most of the above applies to metal working machinery, how does
it transfer to wood working tolerances?

You can machine a metal piece +\- 0.001" and come back a month later
and find the piece to still be within spec assuming ambient
temperatures are similar.

Machine a piece of wood to the same +\- 0.001" in the morning and it
will be out of spec in the afternoon.

Basic reason any material that gets machined, gets glued up the same
day, at least in my boat yard.

IMHO, expecting to maintain wood tolerances greater than +\-1/64" over
any length of time is a stretch.

Lew