How to test and fix a framing square if you think it's not giving perfectly straight cuts and lines.

A framing square provides numerous tables and aids that solve many carpentry and framing problems. But perhaps its most-common use is to draw a straight line at right angles to a board or piece of siding or metal in order to make a straight or "square" cut across the board end.

If your square cuts are inconsistent or not square, here you will find the causes and cures for that aggravation.

Is Your Framing Square Square?

Are your "square cuts" really square? Why not?

If like I have done you've often used your framing square as a saw guide, you may notice that your "square cuts" are not always perfectly square.

If the ends of your boards are not square across there are several probable causes in order of likelihood:

1. Your lumber was curved and you didn't notice it - hold the board edge up and sight along its edge for a quick check. If the lumber is curved holding your square's long side or blade along the lumber won't give a 90-degree end cut.
2. You were careless: You didn't hold the framing square blade or tongue tightly along the side of the board you were cutting - oops.
3. Your saw blade is whacked out of adjustment or the saw shoe or saw guide has been damaged. I once drove my pickup right over my Milwaukee worm-drive saw. Amazingly the saw seemed to survive perfectly well, but a few cuts later I saw I needed to straighten the shoe.
4. Your framing square itself is not true. This may seem rare but our carpenter's helper, assigned to mark out square cuts on a batch of deck joists cut every joist out of square. We found that her framing square, a .... shall we say inexpensive model bought offshore from that country who's been subject of a trade war ... was in fact out of square.

Here we show how to check if your framing square is square or true: a perfect 90° and if it's not we have a tip on making it true.

How can you suspect that either you're not handling your tools accurately or your framing square or saw guide is not a perfect 90° angle? Here's what I do.

Follow the text together with a look at my drawing just above.

5 Steps with Two Boards Test your Square End Cuts for Squareness

1. I use my framing square or saw guide to take my best shot at making a square end cut on board A.
2. I do the same thing again, making a square end cut on board B.
3. Then I flip board B over so that what was its "bottom" surface is facing up, keeping both board ends oriented otherwise the same way.
4. Then I put board B atop board A and feel along the board sides to make them dead straight atop one another.
5. Then I push the two board ends to be as flush to one another as possible.

If the board ends are not dead smooth across after flipping board B over and putting it atop A, then my straight cuts are not straight.

How to Use a Board & a Pencil to Check and True-Up your Framing Square to a Perfect 90° angle

OK so your end cuts are not square and you're convinced it's not you and not your saw. Let's test the framing square itself to confirm that it is or is not perfectly square and true.

Find a dead straight board that's 8" or wider; you can use plywood, paneling, or any wood material that has a dead straight edge; you can check the edge straightness if you've got a good quality 4-foot level or metal saw guide that's already straight.

1. Scribe test line #1: As we show above, put the blade (the long arm) of your framing square along the board's edge and scribe a thin but clear line along the tongue.
2. Flip the Framing Square Over

1. Scribe test line #2: as shown just above, draw the same line again at the same point on the lumber, again using a thin, sharp pencil.
2. Compare the Two Test Lines: are they atop one another or dead parallel?

We illustrate three possible results below.

Case 1: (above) the two scribed lines are dead parallel or atop one another: the framing square is true or a perfect 90° angle inside the framing square heel

Case 2: (above) if the lines cross then the square is too "open" - its inner angle is actually MORE than 90°

Case 3: (below) If the two lines form a Vee then the square is too "closed" - its inner angle is LESS than 90°

Believe it or not, since the error is likely to be very small, you can usually true up your framing square using a nice heavy hammer and a center punch.

Watch out: do NOT make these adjustments before you've run your framing square accuracy check test a couple of times, since if your lines were not drawn carefully the problem could, again, be you, not your square.

How to True Up a Framing Square that is too open or too closed

To CLOSE UP a framing square that is too open (heel's inside angle MORE than 90°) punch 3-4 dents along the OUTER THIRD of the framing square heel as shown by the yellow dots and orange text and arrow in our sketch.

To OPEN UP a framing square that is too closed (heel's inside angle is actually LESS than 90°) punch 3 or 4 dents along the INNER THIRD of the framing square heel as shown by the green dots and green text and arrow in our sketch. Obviously this punching is easier and more-effective on an aluminum framing square but it'll work on a steel square too.

Check the framing square's trueness again and whack away on the square's heel's other side if more adjustment is needed.

An alternative to pinging the heel of your framing square to open or close it using a center punch is to set the heel on an anvil and whack the outer corner (to open up the heel) or inner corner (to close up the heel) using an iron mallet. I'd reserve that pounding for cases of larger framing square errors.

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Continue reading at FRAMING SQUARE USER'S GUIDE - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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