Is my square square?

[Herb G]

How do you tell if your square is square?
I know about the 3-4-5 method.
But how do I know my square is indeed square?

I ask because I just can't afford a Starrett square.
I'd like a decent combo square.
Heck, I'd settle for a small wood & brass square just so I can check stock.

Any help is greatly appreciated.

[barryvabeach]

Put the try square on a sheet of stock with a straight edge and draw a line, flip the square over, and line it up with the line you just drew - so long as the stock has a straight edge, it should line up exactly, if not, it is off.

[Hank Knight]

+1 for what Barry said. If your square is not square, the angle berween the blade and the first line you drew is twice the error. Flipping the square over doubles the error.

[Herebrooks]

You always wonder don't you. If you do as Barry suggests, it will give you a good indication, but I always wonder just the same. The inherent tolerance of wood from an engineering perspective is 1/16th of and inch, meaning that's what you can count on. That's little consolation to most of us.  I guess it depends on what you are doing that matters. Back to the square. Having a starrett square will not help your woodworking tolerance, a system of checks probably will.

[Admiral]

Herb:  Harry Epstein sells PEC squares that are "blems" deeply discounted.  These are pretty good squares from a good maker, and I've not seen any out of square, and I've resold many over the years.  Here's the link, for $24 you can get a 4r scale (pay attention to the markings on the scales), as well as double squares, etc.  This question comes up once a year and others have bought so they might chime in as well.  Here's the link:

http://www.harryepstein.com/index.php/cl...etail=2797

[Bibliophile 13]

You've been given good advice. The PEC squares (sold under various store brands, including Woodcraft and Lee Valley) are certainly accurate enough for woodworking. To check the accuracy of the square, do exactly what Barry and Hank suggested. Use a very fine pencil or even a knife for maximum accuracy.

Funny story while we're on the subject: back when I was a poor graduate student, I needed a decent square but couldn't afford one. So I grabbed a short length of a wide board with one edge jointed. I went to the local Sears and checked out every square on their shelf until I found one that was acceptably square. I bought it, and I'm still using it to this day.

[Admiral]

Funny story while we're on the subject: back when I was a poor graduate student, I needed a decent square but couldn't afford one.  So I grabbed a short length of a wide board with one edge jointed.  I went to the local Sears and checked out every square on their shelf until I found one that was acceptably square.  I bought it, and I'm still using it to this day.

I do the same sort of thing when buying a new tape measure; I take a 24" Starrett rule with me, and check the tape measures against it for accuracy; its amazing, generally I have to check a half-dozen to find one that is spot on, most are off by 1/16 or 3/32 over the 24", which adds up over a 6 or 8 foot measure.....

[Bill Wilson]

I've picked up a few vintage squares at various tool meets/flea markets/antique shops, etc.  and I run into the issue of how to check for square.  I know how to do it, but at these kinds of places, there usually isn't a suitable surface, with a clean, straight edge to work with.  Display tables just don't cut it and any surface that is suitable, probably isn't one I would feel comfortable drawing lines on.  I've brought a few home that aren't really all that useable, due to being out of square. Fortunately, I didn't buy them because I needed them, but because I thought they were interesting.  It would be nice if they were closer to square though.  Perhaps I should carry a drafting triangle with me when I'm rust hunting. 

[Herb G]

Herb:  Harry Epstein sells PEC squares that are "blems" deeply discounted.  These are pretty good squares from a good maker, and I've not seen any out of square, and I've resold many over the years.  Here's the link, for $24 you can get a 4r scale (pay attention to the markings on the scales), as well as double squares, etc.  This question comes up once a year and others have bought so they might chime in as well.  Here's the link:

http://www.harryepstein.com/index.php/cl...etail=2797

Thanks for the link. They have some really cool tools there.

[Derek Cohen]

Get one of these squares, and never be out again ..

https://flairwoodworks.com/2013/04/01/ma...ow-i-work/

Regards from Perth

Derek