Also, check out the accompanying YouTube video:
You start by using a piece of plywood with one good edge. Either the factory edge that was cut when you bought it, or one you cut with your table saw. If you don’t want to make marks on the plywood, tape a piece of paper to it, and mark on the paper. Lay the short edge of the square along the plywood, draw a mark the entire length of the square. Flip the square over, and move it about 1/16″ of an inch away from the other line, and draw a second line. These lines should be parallel. You will see from the video above, that for a framing square, you can use a center punch and if your square is less than 90 degrees, hit the inside corner, if your square is more than 90 degrees, hit the outside corner with the center punch (hard), on a metal vise. This spreads the metal out ever so slightly and will move the angle of your square slightly. Be sure and check it again on the plywood, again making two marks with the pencil. See if you need to do it again. You can make several punches in a small area to spread the metal more and more if needed. Make sure and don’t go too far. Also don’t get too close to the edge, or you may mess up the straight edge, and you’d need to file that down.
I did see online where some squares did not have parallel blades. This means the outside edge may give you a square, but the inside edge would not! That’s no good. Always check your squares right away when buying them. I’d return one that didn’t have parallel blades. But it is easy enough, and apparently pretty normal to have to adjust squares to make them actually square.
For a combination square, do the same check for square. When tightened down, the blade gets pulled against two tabs inside the slot. Figure out which side needs to go lower, then remove the blade, and you can either file the tab down, or use a piece of 220 sandpaper wrapped around a thin piece of wood, sand the tab a little lower. My combination square has an aluminum head, so it was easy to sand the tab down. I rechecked several times, so I didn’t sand it down too far.
At this point, make sure and try to be careful with your squares. Dropping them will probably mess up the alignment so it is no longer square. When you sit a square down, make sure it is in a place where it won’t accidentally get knocked onto the floor later.
I also have a couple engineers squares. These are very precise squares, and you can check your tools blade and fences to make sure everything is very square. Don’t drop these! I did see how you could get them back into alignment by sanding the edge with sandpaper, on a flat surface, but you have have to do the inside and outside edges, and this seems like it would be very difficult to do.
Tools used (click to check out the tool on Amazon):
A center punch:
A framing square:
An affordable combination square:
The Rolls Royce of combination squares, a Starrett with square, center and protractor – click here to check it out!
An engineer’s square: