When you’re building casework, your parts really need dead square ends if you hope to fit drawers, dividers or a gallery inside.
I don’t trust any table saw gizmo to give me square cuts. And I don’t trust my shooting board, either. The only thing I trust is a square that has been tested for accuracy.
To check my carcase parts, I have a couple of huge Starrett squares that are pure indulgence – one of them I picked up for cheap because the seller was trying to make a quick sale. The other I bought to reward myself for completing the writing on a book.
But you don’t need these fancy squares to do fancy work. For years I used two other cheap options to confirm my cuts were square: An inexpensive framing square from the home center or a wooden square I made.
I prefer the wooden square because it’s easy to true it up with a block plane if it goes out of truth.
The framing square is my second choice. Most of them are reasonably square from the store, but you can correct them with a punch or nail set if they are out of square. You do this by punching at the corner where the two legs meet.
If the square is less than 90°, punch near the inside corner. This spreads the legs out. If the square is greater than 90° you punch near the outside corner, this pushes the legs in toward each other.
Some framing squares are easy to adjust; some will resist this operation. I haven’t found a pattern that explains why this is the case, I’m afraid.
Another option is to make a square from Plexiglas. The factory-cut sheets are usually dead square. If they aren’t, glue on a wooden handle to one edge and adjust the handle so it reads square.
No matter which way you go, get used to using the square before you dovetail anything together. It will save you from grief time and again.
— Christopher Schwarz