How Square is Your Square?

[Sam Puhalovich]

I hadn't had much luck with verifying the 'squareness' of my squares. As it's turned-out of my assortment of 10 squares ... I have 2 12" adjustables are dead-on ... as I can measure. The rest are all 'out' in varying amounts. I've been stumped about how to measure the 'squareness'. While reading thru the "Which Parallel Guides for Makita Track Saw" thread: something caught my-eye in one of the 'attachments' and decided to try a set-up comparing the square to itself.

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This is a variant to the 'flip' method. The picture shows the square in the flipped position with a .036 feeler guage ... showing that the square is .018 out-of-square. Using a Veritas straight-edge for a base ... the square was first placed at the opposite side of the pins (2, 1/2" shank router bits) and the pins aligned to touch the square. When flipped: the square was slid to touch the 'nearest' pin ... the gap to the 2nd pin being the 'doubled' amount of out-of-square.

I'm looking forward to seeing posts of other methods.

[Jim Becker]

While I know the focus of this thread is on "squareness of squares", the same concerns come with the "sameness of scale" when it comes to other measuring tools. It's a really good idea to check things, especially if there is a variety of brands and sizes involved. Squares in the woodworking shop need to be as accurate as possible because of the detail level of the work we tend to do in our projects. Rules need to agree as we switch between them for the same reason. Unlike in general construction where there is often a little wiggle room (aside from certain finish carpentry tasks where inaccuracy would be visible) woodworking projects in our shops turn out best when angles and measurements are in agreement.

Stan, that's an interesting method to test things. I'm also looking forward to variations from the community.

[Ole Anderson]

I made my own "square" by cutting an 18" piece of baltic birch to a square using the 5 cut method, getting the last off-cut to within a few thousandths, and attaching a raised edge (lip) to it. I use it for marking plywood to break it down with my track saw.

[Steve Rozmiarek]

Same idea, different process, just get one that you use as the master square or measure, and check everything else off it. Don't use the master for anything other than tool checking. I personally have a big old framing square that has been tuned to "perfect" using the flip, and a Starrett yardstick that serve that purpose in my shop. I don't bother with the carpentry tools, but the shop tools get checked.

[Prashun Patel]

I usually just check two good ones up against each other using (I guess you'd call it) the spoon method. It's quicker and doesn't require me finding a reference board with a straight enough edge. When doing precise work, I will double check my strike marks with a second square (or if there's room) the flip method.

I suppose this assumes you have at least one that you trust.

[ChrisA Edwards]

I recently bought a cheap combination square. I used it mostly for measuring distance from the edge, so the squareness never really got tested.

Then I did the pencil test to eyeball the squareness and it was a mile out.

I hate throwing anything away, but that one went in the trash.

Of all the squares I own, mostly Woodpeckers, all were bang on.

[Matt Day]

I do the flip method. Place it against a known straight edge and draw a line, flip the square and draw another line and see if they match up. The difference of the lines is how far out of square it is.

[Kyle Iwamoto]

Personally, I use a drafting triangle. The plastic one. NOT the cheap ones from Wmart, I got mine a drafting store. They use it to draw plans for buildings and bridges. Oh. Sorry, I'm old, they use Autocad now. But they USED to draw plans with them. Good enough back then, good enough for me.

[Bill White]

I'm with Kyle. I use a Staedtler drafting square to check all my tooling. Simple, quick, and painless.

[Thomas Wilson]

I recently bought a cheap combination square. I used it mostly for measuring distance from the edge, so the squareness never really got tested.

Then I did the pencil test to eyeball the squareness and it was a mile out.

I hate throwing anything away, but that one went in the trash.

Of all the squares I own, mostly Woodpeckers, all were bang on. You can adjust a combination square by filing the reference points in the slot of the head. Cheap squares are made of soft metal that wears quickly so you have to recalibrate regularly. When the reference points are filed down flat then toss it.

[Bill Yacey]

I'm with Kyle. I use a Staedtler drafting square to check all my tooling. Simple, quick, and painless. It depends on the size of the drafting square; the larger the square, the more runout accumulates as you get further out from the right angle corner. If your reference square is smaller, like an 8x8", this might be too small to check a large framing square.

[ChrisA Edwards]

You can adjust a combination square by filing the reference points in the slot of the head. Cheap squares are made of soft metal that wears quickly so you have to recalibrate regularly. When the reference points are filed down flat then toss it.

Appreciate that, I was aware of this fix, but this was so far out, that I was disgusted with it and it gave me an excuse to buy a better one (Starrett), which I should have done in the first place. I did check that one as soon as it arrived.

[Bill Yacey]

You can also use Pythagorean 3.4.5 to check a square if you lay it out carefully.

[Cary Falk]

I have some Incra and Woodpecker squares so i don't have to check for square. I have far fewer issues since getting rid of all of the other cheap squares.

[Matt Day]

Drafting triangles are good for many things, but I find that having a few accurate squares are necessary. For instance, I have a go to 2” and 6” Starrett [slow iPhone 11 and safari] squares, and a 12” Woodpecker.

[Alex Zeller]

I have a 24" Starrett combination square that's probably the most accurate square/ straight edge I have. But since the blade is not fixed I check it before making anything critical with a small machinist square. I also have a reference board like Ole uses. I made it to fine Incra 1000HD miter gauge.

[Derek Cohen]

If you want a reliable and accurate square, get a decent machinist type. These must be steel-riveted-to-steel.

If you are feeling flush, get yours from Chris Vesper. The best woodworking squares in the business. I have a 4” and 7” ...

https://i.postimg.cc/RhrsgFS2/Vesperat-WIA3.jpg

Regards from Perth

Derek

[Thomas Wilson]

When I got to the shop this morning, I checked most of the squares I have there. I have a few more in the Atlanta shop. I taped a page from my sketch pad to the table saw and used a 0.5 mm mechanical pencil to draw a line, flipped the square and drew another line to check. I used the edge of the table as a reference for the squares with a lips. I clamped a high accuracy straight edge (36 inch iGaging reference straight edge) for squares without a lip. Only the 26 by 16 Woodpecker was noticeably out of square. I noticed a ding on the corner of it so that is probably the cause. I would say a 0.5 mm pencil does not give a fine enough line for a highly accurate test. Maybe poster board and a marking knife wood be better. This what I had on hand.

I have been using my aluminum drafting squares a lot in building Chinese Chippendale panels for a handrail. I like the aluminum for woodwork better than plastic.

Here is an ensemble shot of the squares. My everyday Crafrsman combination square and Swanson speed square were out on the porch and did not make it into the pic. The test sheet is under all the squares. Fun and useful test. Thanks for the post.
s.439751

[Stan Coryell]

Personally, I use a drafting triangle. The plastic one. NOT the cheap ones from Wmart, I got mine a drafting store. They use it to draw plans for buildings and bridges. Oh. Sorry, I'm old, they use Autocad now. But they USED to draw plans with them. Good enough back then, good enough for me.

Funny story. My ex father in law built model boats. He laid the keel for one out on paper. He couldn't come out right when he mirrored it. He asked me to take a look at it. I checked it with dividers and his perpendicular line is out of 90. As he add parallel lines, it compounded. But, you couldn't really see it until he tried to mirror it. So, I show him how to mark off the parallel line with the dividers. He tells me, "that can't be right, I used this drafting triangle!"
Well Joe, the triangle is out of square. He never did believe me. Boy was he stubborn, he daughter was exactly the same....