One of my most often used tools is one of my combination squares. They are essential to the laying out of joints and checking that assemblies have been joined correctly, but I also use them for everything from depth gauges to laying out for planing boards to the proper dimension. If you decide that you would prefer the heresies of not using the right angle (hint: it’s called “right” for a reason), then you must be a chairmaker. Or a creator of “modern art”. Or both…
Anyway, I have four combination squares that I use. All are Starrett.
From left to right: 18″, 12″, 8″, and 6″.
I use the 6″ square for laying out most of my small joinery, dovetails especially. Most of my marking and squaring of stock while I dimension it from roughsawn gets done with the 12″ and 8″. I keep the two of them on hand since I can set two different dimensions and keep them unvaryingly recorded while I work, while also being able to use them for checking square and knifing cutlines.
The more unusual square, and one that becomes incredibly useful once you get into large casework, is the 18″ square. If you work on anything larger than 9 or 10 inches wide, you will find that the 12″ square isn’t big enough. It doesn’t make sense at first, until you realise that some of the square’s beam must be inside the stock for the locking nut to bear on. So even though the beam is 12″ long, you only get about 10″ of working length. For working on anything larger, you would either need to square from both sides (which is not optimal for accuracy) or use a larger square. You can use a framing square (I did before I finally bought my 18″ combination square), but it is much more unwieldy in use.
Unlike the try squares of old, combination squares do more than gage 90º angles. The basic stock also has a mitre side, and usually they incorporate a level, which proves quite useful on occasion. In addition, the beam can be transferred to a protractor (which we’ve used this past week) and a centre finder. Both have their uses. Finally, the hash marks that usually delineate 8ths, 16ths, 32ds, and 64ths of an inch (metric beams are also available) are actually cut into the metal beam. This permits you to precisely set a pair of dividers by setting the points into the desired hash mark.
All in all, the combination square is an important addition to my toolbox, and I believe you would be remiss not to have it in yours as well.