GGS,
Steve asks about how to square squares (you get quartics).
Snip>
>I started checking all
my squares for a true 90, by putting them on a straight board,
scratching a line, flipping the square and making another line.
I was appalled when I found that the squares I had been trusting to be
correct were *WAY* out of square. This includes a machinists square from
a well known mail order company that has *NEVER* been dropped or
mistreated in any way.
So is there any way to fix squares that are not?
Ouch- I would be tempted to send that square back to the mail order
company for a replacement- and explain why. In the long run, a machinsts
square is nice to have, even if only to tune other squares. Or a minty
Starrett combination square (thanks Patrick) which is reserved for
special cases- you don't want to drop them!
The easiest way to true a square is- to hold the steel blade on the
floor and give the handle a whack with the heel of your hand. And if it
needs more encouragement, a decent tap with a mallet. If you go
overboard, you could induce some twist in the blade- so be careful that
you never hit real hard, that the blade is supported, and the direction
you whack is in line! I have tuned a fair number this way, no problems
yet. In every case, I have been able to move the blade to make the
square as good as the blade edge tolerance (usually these are not ground
totally straight, and you can't make 2 kinda straight edges perfectly
square. And if the blade edges aren't parallel, you gotta choose between
lapping, making the inside square, or making the outside square.
The cheapo new squares can be pushed together (or apart) with hand
pressure alone. I have moved an older one an 1/8" (over a 6" blade) this
way. Of course this technique has its limits, after a point you do have
to lap off. But I have had much more success than with hitting rivets.
I don't think this will work real well with a machinist style solid
steel square, although I have used it with success on an older all metal
Stanley.
>I figure that the adjustable combination sqaures are not fixable,
Well, you are wrong here. Whilst travelling, I picked up a 6" Union
combination square in what looked good shape- but I didn't have a
"mother Square" to test.
It turned out pretty lame, so I started to lap the blade on my scary
sharp setup- much easier than when the blade is fixed... Veterans will
know where this eventually leads. This still seemed like hard work, so I
had the sudden insight- take a knife file and carefully file away,
adjusting one side of the inside of the head, where the rule rests when
pulled tight (this is the real trick!) Might not work on hardened heads-
but they should tend to stay more true in the first place.
To make a long story short, the square was better, but still off- I
could make the inside square but not the outside. Took me longer than I
care to admit to determine the 2 edges of the rule were not parallel-
and that I may have had a part in this..
The proper order:
1)check that the edges on the rule are straight and parallel. If not,
make it so!
2) file the slot (carefully) until you get square.
Wade
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