I think that's the same set I bought at Woodcraft. The precision of
(IIRC) 0.0006" is marked on the blades, but no indication of whether
that's overall or per inch. In either case, I set the 6" up against a
pricey machinists square on a flat surface and there was absolutely no
light between the blades. I'm happy.
Intelligence is an experiment that failed - G. B. Shaw
The precision should be per inch.
While they are on the lower end of accuracy for squares used for setting up
metal cutting tools, their precision goes beyond anything that is likely to
be detectable in woodworking. Face it, there's nothing magic about
machining two pieces of steel flat and sticking them together at right
angles--they can do that as well in India or China as they do in the US and
Japan and the EU.
The place to spend the bucks is with a combination square--there the cheap
ones usually aren't square out of the box and if they are they don't stay
square very long--since they have moving parts, maintaining precision is
more difficult than for something that is permanently welded/brazed. I
finally spent the bucks for a Starrett and I'm glad I did. Browne & Sharpe
and Mitutoyo also make good ones.
On Tue, 24 Nov 2009 06:56:42 -0500, J. Clarke wrote:
I've got one of the first squares from Stanley Rule and Level Company.
They put the handle and the blade in a jig and poured molten metal into a
matching set of holes. After all these years, it's still right on!
Intelligence is an experiment that failed - G. B. Shaw
A few years ago, long before I found this forum, I bought two
carpenter's squares, 24" and 8", believing that I was starting my
woodworking tool collection. I assume they may be good for deciding
flatness and maybe cutting some square (replacement) pieces of drywall
and as a replacement for a steel rule (?). I anticipated using them
as a try square on wood, but from what I've read here they don't make
the grade.. Does anyone here use carpenters squares for anything
(besides stairways and roofs)? Probably precise enough to use on
outdoor furniture, huh--or better than that?
You'll never regret buying a good square. However, they're only good 'til
the first drop, so consider how (and where) you'll be using it. For the
purposes you describe, I don't think you can go wrong with the Groz. If
you're still not sure, buy the Groz, take it to your shop and see how much
or if it's off square, and if that doesn't meet with your minimum
requirements, take it back and tell them it's not square and step up to the
The only "test" I can think of is the one I learned for a carpenter's
square: You use the square to draw a perpendicular line to the edge of a
board, then you flip the square over and draw another line. The lines
should be the same or parallel. Repeat several times for higher
confidence. How does that test measure-up here???
If you don't already have a known-good square, then that test works.
You need to make sure that the edge you're referencing the square
against is straight. If you're using a wooden surface, a knife will
give a finer line than a pencil.
If you've got a known-good square (a drafting triangle works fine) then
take it and the one being tested and place them both facing each other
against a known-straight edge. Hold it up against a light and see how
big the gap (if any) is between the two blades.
If you wish to check that your TS blade is vertical, for instance, do you
just use the base of the double square?
It would appear that the base has the potential to have more "integrity"
than the angle it forms with the rule.
I like that it is graduated--seems very usable indeed.
My thanks to everyone who has helped with this thread!
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.
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.
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