A Geeky Tool Post:
While going through some of the tools we acquired just before Pennsic, I found the holy grail of combination square rules! Obviously, this needs a big footnote, so let me explain. I use 3 Starrett squares on almost all of my projects. I have a 4″ double square, a 6″ double square, and a 12″ combination square.
Mostly, I use them to check for square (usually the 6″ double square, but if it’s tight or small, I use the 4″ one). I also use them to layout cuts (mostly the double squares), or draw lines that probably should be done with a marking gauge. Only occasionally will I actually measure anything, and that’s mostly with the combination square. Which is good; measurements are the devil, but it’s sometimes unavoidable.
Now, for some arcane tool knowledge, this is the deep stuff. There is a standard to the markings you find on rules. This standard specifies how rules are marked. The various recipes are numbered. Almost all combination squares you likely run into are type ‘4’. Except for the true bargain brand stuff, they will have a marking like: ‘GRAD. 4R’ somewhere on them. ‘Grad’ stands for ‘graduated’. The ‘4’ means it will have a set of scales in 8ths and 16ths on one side, and the other side will have scales in 32nds and 64ths. The ‘R’ means it’s a rule (as opposed to a ruler). Rules start at the edge of the blade. A ruler will have a little space before the markings start. Yeah, I never noticed that before, either.
So, to me, the combination square is one-sided; I can’t even distinguish 64ths. For many things in woodworking, a 1/8 is good enough. For demanding work, like joinery, you can go to 16ths. A perfect Grad system for woodworking would have 8ths and 16ths on both sides. I know from an early 20th-century catalog that Starrett made such a rule (the rules are interchangeable in the square’s stock), but I have never seen one.
Well, I finally found one in a box of other machinist tools. It needed a little cleaning, but that’s one of the things we do here. It came with a bunch of other stuff, so it was essentially free. Now it’s mine, and I can sell the 4R for $20 and come out way ahead.
The pictures show the square with the No. 94 rule and the standard No. 4 for comparison.
