Combination Squares

Posted by Easy WoodCraft on

Jan 28, 2016

What do you get when you combine a metal rule, try square, miter square, level, and depth gauge into one tool? A combination square. A combination square is a metal rule with a groove in it that accepts a pin in the head of the square. The head has two faces—one at 90 degrees and the other at 45 degrees. When the knurled nut on the end of the pin is tightened, the head locks the rule in place at the desired location. Some heads also incorporate a spirit level, but the short length of the head (typically 4") limits its usefulness. While most combination squares come with only one head, there are two other accessory heads that are quite useful: a center-finding head and a protractor head that adjusts to any angle from 0 to 180 degrees (inset).

As a try square

Probably the most ordinary use of a combination square is as a try square. The advantage to using a combination square is that you can adjust the blade to the desired length. Also, since its head is metal, a combination square is usually more accurate than a try square with a wood stock.

As a depth gauge

Another frequent use of a combination square is as a depth gauge. To use one for this purpose, loosen its knurled knob and place the 90 degree face of the head so that it spans the hole to be mea­sured. Make sure all chips are cleared from the hole, and then lower the blade until it bottoms out. Tighten the knurled knob and remove the blade to read the depth.

Parallel lines

By far the most common reason I reach for a combination square is that I need to mark out a line parallel to an edge or a series of parallel lines. The combination square really excels here. Say, for instance, you want to lay out a series of lines on a fireplace mantel where you're going to carve a set of flutes. Just set the blade the desired distance from the edge of the work-piece, lock it in place, and then butt the head up against the edge of the work-piece. You'll note that there's a small notch centered in the end of the metal rule; this is for your pencil (or awl, if you prefer). Position the pencil in the notch, and while holding it firmly in place, slide the square along the edge of the work-piece, keeping steady pressure on the head.

PARALLEL LINES WITHOUT A COMBINATION SQUARE

If you don't have a combination square and need to lay out parallel lines, here are a couple of ways to do it. I had an old-timer woodworker friend who could mark out parallel lines with just a pencil with unbelievable accuracy. He'd hold the pencil in his hand and use his fingers as a stop to position the pencil where he needed it (top photo at left). He'd been doing this for so long, he could hit a mark within about V32". Although I'm not that accurate, I often use this method when I'm marking out a detail that doesn't require absolute precision, like the chamfer around the edge of a table top.

If you've got a lot of parallel lines to draw that need to be precise, consider constructing a simple shop-made square (bottom photo). It's just a block of wood that's notched the desired dis­tance in from the edge. A kerf in the end of the scrap accepts a pencil to draw uniformly accu­rate lines.

CENTER-FINDING TIPS

You'll frequently need to find the center of a work-piece. The combination square is the per­fect tool for the job. Here are three different ways to use it to locate dead center.

Marking diagonals

The first and simplest method to locate center is to use the 45-degree head of the square to mark a series of diagonals. This method works best with stock that is relatively square, since sides that are not 90-degree can throw the center-point off.

Using a center-finding head

If you've purchased the center-finding head for your combination square, it doesn't get any easier than this. Just slip the center-finding head on the blade and position the head so it touches adjacent sides of the work-piece; then mark center. This head is especially useful for finding center on round stock.

With a framing square

The only disadvantage to the methods described above is that they work well only for relatively small work-pieces. If you have a work-piece that's larger than 6" to 1", you might find that this tip works well: Clamp a framing square to the blade of the combination square so that the long blade butts up against the 45-degree face of the combination squares head. Adjust the blade of the combination square so that it bisects the inside corner of the framing square. Then position the framing square so that both its legs contact the work-piece, and mark the center.

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