Swingman wrote in
:

On 3/14/2010 12:32 PM, Doug White wrote:

I've heard of this approach, and the large square is probably close
enough to give it a shot. I suspect I'd have to beat the hell out of
the smaller square to get is closr to right.

It may help if you mention what it is that you are making that takes
that kind of "squaring" precision out of a framing square that is
normally good for the proverbial "1/8th in 8" on a good day (not
including pitch, rise and run, rafter layouts, etc, ot course.)?

When a competent carpenter/framer needs more of such precision over a
distance than inherent in a "framing square", he uses math.

This is for cabinet making, of a sort. I have an aluminum frame that I
am fitting shelves to, and the frame is eminently square. It's made from
80/20 structural aluminum (http://www.8020.net/).

My ShopSmith table saw is a wonderful tool, but the miter gauge is the
weakest part of the system. Cutting 14" wide shelves resulted in errors
close to a 16th of an inch. (Yes, I know, I should make a sled). I
wasn't surprised, and had planned on straightening things up with my
router. I checked the shelves initially with a general purpose
combination square. To set up a guide for the router, I grabbed my
smaller framing square, which showed that the shelves weren't nearly as
out of whack as I first measured. That's when I discovered that no two
of the four wood working squares I tried agreed. I went to my machine
shop and got out my "serious square" and found errors of one sort or
another in all of them. The worst is the smaller framing square.

Doug White