Checking a Square Before You Buy





Introduction: Checking a Square Before You Buy

This is my old framing square. It has taken a lot of abuse, mostly from things I have done in attempts to make it more accurate that did not turn out as well as intended. I have thought about simply replacing it.

I looked at new framing squares on-line. Reviews were mixed. Some found the square they purchased to be square. Others found the same makes and models not to be square.  

This Instructable will show an easy way to check a square accurately in a store before buying, and it will offer a surprise to consider when looking for a very accurate square.

Step 1: A Little High School Geometry

"Two lines perpendicular to the same line are parallel to one another." is a first-year geometry theorem. No one was watching me in the store, other than the security cameras, so, I pulled three identical squares from the rack and spread them out on the floor. Their labels did not wrap around the square, which would have compromised my test but the labels were only stuck on the surface of the squares. I used one square as a straightedge. I slid the other two squares against this side. Then I slid them toward each other. I was careful to be certain the squares rested firmly against the straightedge. If the squares are really square, the vertical edges should meet along their length. Notice the gap between the edges where the two squares meet each other, especially how it forms a shallow "V" that becomes wider at the upper part of the photo. These squares are not square. See the second photo from a close-up photo of the gap.

I had checked framing squares this way in two other stores, but had not thought to take a photo. These squares are shorter than a framing square. This particular store had only one framing square on the rack, so I chose to test these shorter squares. The framing squares I checked in other stores all had a "V" gap, too; but, the gap on the squares shown here was the most severe.

One lesson learned is that squares off the rack in all price ranges may be accurate enough for framing houses with 2 x 4s, but those I checked are not good for precise work, like making furniture, without making adjustments with an anvil and a ball peen hammer. (This method for adjusting a square makes a dimple that brings the legs of the square nearer to each other or pushes them apart, depending on where the dimple is placed in the corner.)

Step 2: Surprise!

This is called an "L" Connector. They are in the portion of big box home improvement stores where you find corner brackets and similar things for connecting joists. I had long wondered about them and they are surprisingly accurate as squares. The legs of the larger "L" Connector are 12 inches in length each.

Step 3: Test

I used three "L" Connectors to apply the test I showed in step 1. All of the edges met very nicely. See also the second photo. Whereas there was quite a gap between adjoining edges in the second photo of step 1, here the edges meet very tightly. The apparent gap at the very end of the two "L" Connectors is not due to any lack of squareness, but the edges are made with a little recess on each. The edges are still parallel.

If you choose to purchase an "L" Connector for use as a square, do not take what I have presented here at face value, but pull three from the rack and lay them out on a flat surface as I have shown here and check them, yourself.

Step 4: Applications

I chose to buy an "L" Connector just as a reference check for my other squares. It would suffice for an inexpensive square with very good accuracy. It could easily be adapted for use as a try-square. See this Instructable. If done carefully, the legs of the square could be extended by placing the legs against something straight. Bring a straight bar against the straightedge and clamp it to the "L" Connector. Drill holes and rivet or bolt the pieces together very firmly.  

I did make one little modification to the "L" Connector. The inner corner of the "L" Connector came with a round corner. That would make it difficult to use as shown in the photo. I used a file to make the corner square.

I am still thinking about whether I will work at improving my old framing square or replace it. The "L" Connector used as a square has given me a better idea than I had before of the exact problems that need correction. 

UPDATE (April 25, 2013): I was at Harbor Freight last evening and tested their framing squares. They were accurate, so I bought one. Today I was also at an Ace Hardware and their framing squares were accurate, too. My old framing square will be used with welding projects that need to be somewhat square. Since it is far less than perfect in several respects, it will not matter if weld spatter encrusts it. 



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Flipping the square to test the accuracy of the two lines, as Phil B and Pfred suggest, is pretty much the way I check my spirit level. Lay the level on a flat surface, mark the position then check the position of the bubble. rotate the level 180 degrees, ensuring it is in the exact same place that you marked. The bubble should correspond exactly to the position you first noted. If it does not then the level is out.

You make a very good point. I had never considered checking a level in that way until I was working on a wheelchair ramp project with a man older and more experienced than I. He consistently took two readings with his level, turning it 180 degrees between the readings. I generally do that now, too.

yep, puts another hat on measure twice.

Thanks this instructable is very helpful!!

Thank you for looking. I am glad you can use it.

Wow! this is just great!

thank you for looking.

I,too have run into squares that were inaccurate off the shelf numerous times, even smaller ones like an aluminum speed square. There is a technique I saw in fine home building years ago for recalibrating a framing square that actually works, although it may involve a little trial and error. Take a tapered metal Punch and lay the square on a flat surface. Hit the punch to make a small indentation either at the outside or inside corner of the square. I haven't done it for a while so I don't remember exactly but I believe hitting the outside corner will close the angle of the square and the inside corner will open it. You may have to play around with it a little bit but it definitely does work.

Thank you for your comment. Yours is a good point. About 40 years ago I found a 1913 print copy of Samuel Griffith's Woodwork for Secondary Schools. I believe it was that volume that mentioned using a punch to expand either the inner or outer part of a framing square's corner to close or open the legs of the square and acquire accuracy. (That book in the 1915 edition has been available on-line free as a PDF download, but I am not certain it still is.)

I once did an Instructable on checking a square for accuracy and making it accurate. At that time my favorite method for restoring accuracy was to dress the blades of the square with a hand file. I had always been hesitant to dimple the corner of a square with a hammer and a punch. I have grown past that and have successfully used either a punch and hammer or the rounded end of a ball peen hammer to spread or close the legs of the square and make it accurate. At the time I did this Instructable I finally decided to replace my first framing square after 40 years. To my surprise, the most accurate framing square I found was a $9 steel square at Harbor Freight. After I had used it a few times, I did place it on an anvil and strike it once with a ball peen hammer. Now it is very good. You can see how I use and simultaneously check that square now at step 6 of this Instructable.

This sounds terrible, but once I found a way to make a square really accurate I began acquiring more squares than I can use in a lifetime, although each was acquired for a different reason and purpose. The best squares I currently have are some I made from scratch. Here is my best, although I have tweaked it a few times after some discovery or accident that made it less accurate temporarily.

It is really nice to use a square and know that my practice in the use of that square is likely less accurate than the square, itself, is.

Good advice Phil. Years ago my dad bought a 10 foot satellite dish and it was up to me and him to install it. He lived 125 miles away, so I told him to set the pole in 1 cu.yd. concrete PERFECTLY LEVEL. I wend down to mount the dish and the pole was crooked. We checked his level and it was inaccurate. :-(