Thursday, November 29, 2018

A Simple Tool for Checking Diagonals for Square

During the glue-up of my recent curio cabinet project, I couldn't use a tape measure or any other straight rule when checking the carcase for square.  That was because I had sides that were not flush with the top and bottom - they were set back about 1.5".  So I made a simple tool with stuff I had on hand.  I've used two sticks before to measure inside diagonals, but they never seemed accurate enough due to slippage.  I'm not sure where the idea came from, but it hit me all of the sudden and I wondered why I hadn't thought of this before.
Veritas mortise/marking gauge and the diagonal measuring tool
The Veritas gauge comes with a little piece that locks the two rods together so that you can get the exact same mortise width in different locations relative to the edge of project parts.  I measured the two rods at 5/16" and wondered if I could lock two pieces of 5/16 dowel rod together using the mortise gauge locking piece.

I put one end of each dowel in a pencil sharpener so that they fit tightly into corners.  Slipped them into the locking mechanism and turned the thumb screw and it worked great.  The two dowel rods stayed where they were supposed to.
Checking one diagonal
And the other
When the gauge fits the same in both diagonals, you know your project is square.

Sometimes it's the simple things in life that make me giddy.  This one did!


  1. Good project
    I long ago ditched the tape measure and rely on pinch sticks for measuring diagonals. So much easier and more precise, I do not know why some still insist on struggling with their measuring tape...

    Bob, who cleaned the gutters and put up Christmas lights

    1. Ah, "pinch sticks". I was thinking there was a name for these things.