Using a Combination Square for Measurements
The sort of combination square you have says a bit about you as a woodworker. The first one I used — for a couple of decades, at least — was a 1940s Craftsman I got from my dad. I used it for home improvement and construction projects and furniture-making work without much thought about its accuracy or about all the different uses I had for it.
Author Billy Hylton uses his combination square to check the settings on a table saw, the tool has multiple uses in many shops. About 15 years ago, I retired it in favor of a Starrett I bought secondhand — a four-piece set with a 24" blade. I hadn’t used this square long before I realized ... well ... it wasn’t square.
Then I discovered a hidden benefit of owning a premium square: the manufacturer will fix it! I mailed it to Athol, Massachusetts, and in a week, the postman brought it back. Good as new!
In short order, I got a second Starrett, a new one with a 12" blade. It was an admission that a 24" blade is really too long for most work. Some time later, conceding that even the 12" blade is too long for close work, I got a 4" square, all top-drawer and a bit pricey. But wait a minute here. Let’s think “practically” for a moment. For about 15 bucks, you can buy a combination square that’s virtually a duplicate of my old Craftsman. In addition, you can buy a 6" Craftsman square and a 16" Craftsman square, each for about the same $15. Why would I instead spend $250? It’s a fair question. What makes one combination square worth $70 more than another? Are the differences significant to a woodworker?
To explain it — to myself as much as to you — I doubled back on myself, doing an inventory of what I do with combination squares and surveying the marketplace. Combination squares have many practical applications in woodworking. Accuracy becomes more and more important as your projects’ sophistication increases. The options before you are legion. You have to look online to appreciate what all is available.
Hardware stores and home centers carry an array of models targeted at tradespeople and DIYers. Woodworking tool retailers stock two or three configurations, hitting low, medium and premium price points. But machinists’ tool retailers go way beyond that. One online retailer lists about 600 items from about a dozen manufacturers in the combination square category.
The Basic Combination Square
The basic tool consists of a head, called a “square head” despite its polygonal shape, and a 12" metal ruler, called a “blade,” that’s graduated, usually with a different scale on each edge. A special bolt in the head engages a groove centered in one face of the blade, so you can slide and lock the head along the blade.Because the groove is centered, you can switch the orientation of the graduations by pulling the blade out of the head, turning it end-for-end, and reinserting it. You can also roll the blade over, but to do that, you have to spin the lock bolt 180° to accommodate the re-positioning of the groove.
The head has three ground reference faces: one parallel to the blade, a longer one perpendicular to the first (and thus to the blade), and the third at 135° to the first (and thus at 45° to the blade). Incorporated into the head is a bubble level so you can check for both level and plumb with the tool. A small scratch awl usually is held in a bore atop the head; this works better for marking metal than wood. This is the combination square a carpenter uses. Every tradesperson has one, too. And DIYers gravitate to such squares, as do many woodworkers. A machinist is likely to have a more sophisticated version of this square, made with different materials, different finishes and different graduations. He’ll have two additional heads: a center head and a protractor head. A square purchased with all three heads is known as a four-piece set. Variations include models with longer blades and downsized models with 4", 6", or 7" blades.
Combination squares, it seems to me, sort themselves into three categories. Superficially, the sort is based on price — low, medium and high. But the prices reflect the materials used, the design specifications and features, as well as the manufacturing procedures. Manufacturers generally focus on a single category, rather than producing squares at each level. Rather than go out to collect and evaluate tools from every single manufacturer, I sampled. I got combination squares from Stanley and Craftsman, two well-know inexpensive brands, and from L. S. Starrett and Brown & Sharpe, two highly regarded premium brands. I also got medium-priced squares from Gladstone, Rockler and Highland Woodworking.
#1 - Low End
In the low-end category are the two-piece squares sold at hardware stores, home centers and lumberyards. Brands include Stanley, Craftsman, Empire Level, Johnson Level and Swanson. On average, they sell for $10 to $20. Widely used by construction workers, tradespeople and DIYers, these are practical tools, subjected to job site conditions, designed for construction demands. One of the givens is reasonable expendability: Drop it off a roof or step on it and you shrug and just buy a new one. Their accuracy may be iffy and their scales a skosh coarse, but they work well. The heads usually are die-cast aluminum or zinc.
The blades are stamped — graduations and all — from a blank, an operation that leaves burrs on the ends and even the edges. Typically, the graduations are 8ths and 16ths on one side of the blade, 16ths and 32nds on the other. Having the most common scale on both sides obviates the need to turn the blade over. There are variations at this level, but not accessories. If you want a longer blade, you can get a separate square with a 16" long blade. But you can’t buy just a blade.
#2 - Top Tier
The top category comprises premium combination squares manufactured primarily for metalworking. Brands include L.S. Starrett, Brown & Sharpe, Mitutoyo, PEC, SPI, and Fowler. Typical prices range from $75 for a two-piece square up to $170 or more for a four-piece set. Prices vary according to the specs of what you buy. The high-end brands give you choices. Sure, you can buy a two-piece set off the shelf. But you can also specify the head (or heads) that you want, as well as the blade graduations, finish and length.
Cast iron heads add durability and a firm base to your combination square, but at a significant price. A square head can be cast-iron or forged-and-hardened steel. The latter is more durable and is often the preference of metalworkers. It’s also more expensive — about $10 or so more. In a woodshop, the cast-iron head is just fine, and it’ll be more durable than a die-cast metal head. Less expensive squares have a lock bolt that rotates freely in its bore when the the blade is removed, leaving you to align it by sight. Depending on the woodworking you do, you can supplement the square head.
Lock bolts with tabbed washers are the easiest to use, even when the blade is removed the bolt assembly doesn't drop out, a feature available on Starrett and Rockler squares. A center head is a V-shaped casting with ground reference faces inside the V. A slot for the blade aligns one edge directly in the vertex. A lock bolt allows you to adjust the head and lock it at any spot along the blade. Center heads are usually found on more expensive and high quality combination squares, but it's very useful for centering pieces. You use this head, as its name suggests, to locate the center of a round — a large dowel, for example, or a turned blank. Hold the reference faces against the round and scribe a line along the blade. Turn the round slightly and scribe a second line. The center is where the lines intersect.
A protractor head enables you to lay out lines at precise angles. Two styles are available. The reversible head has ground reference faces on both sides of the blade, while the nonreversible has this shoulder on one side. Both heads are cast-iron. Either protractor head is fully adjustable with a revolving turret graduated from 0° to 180° in both directions. Either can be positioned anywhere along the blade. Lower cost blades are cut in one stamp, leaving burrs and the chance of slight inaccuracies, while higher cost units are machined and laser etched.
Consider the blade next. A premium blade, first of all, is slightly thicker (3/32" vs. 5/64" for blades in other categories) and thus stiffer. It’s machined from bar stock, hardened and tempered. The graduations are first cut with a CNC machine, then acid-etched to enhance their definition. After it’s ground to final length, the blade is chromed (or satin-chromed), and the graduation marks are darkened. Premium offerings from Brown & Sharpe and Starrett come in different finishes like satin chrome or polished that are easier to read.
You do have a choice of blade finish, as I mentioned. The standard finish, which is what I’ve got and am content with, is polished chrome. But the matte-like satin-chrome finish is non-glaring and easier to read. Had I realized, at the time I bought my Starrett, that this finish was available, I would have chosen it, even at a higher price. Premium blades are made in several standard graduation schemes. The 4R graduation is probably most useful for woodworking, having 8ths and 16ths on one side, 32nds and 64ths on the other. The 16R graduation has 32nds and 64ths on one side, 50ths and 100ths on the other. Metric has mm and .5mm on both sides, while English/metric has .5mm and 32nds plus mm and 64ths. While longer blades might seem like a good idea, they don't work quite as well for small projects.
Lastly, you can opt for a blade longer than 12". Most machine-tool makers offer 18" and 24" blades. Starrett has 36" and 48" as well, though they are frighteningly expensive — jumping from about $90 for a 24" blade to $235 for the 36" to well over $400 for the 48".
#3 - Mid-priced Squares
Finally, there’s the mid-range category, populated with tools labeled Chicago Brand, Gladstone, and General Tool, as well as the branding of retail chains such as Rockler. Almost all are manufactured in China or India. They are priced between the high- and low-end squares, averaging about $45 to $50 for a two-piece set and $75 to $100 for a four-piece set. Sometimes these squares are presented for what they are — better than hardware store squares but not as good as premium squares. But sometimes, indirectly — by implication — they’re presented as being premium tools. The truth is, they are in-betweeners.
Like the low-end combination squares, what you see is what you get: no choices. Most have satin chrome blades, though the Gladstone has a polished blade. Most use the 4R graduation, which is 8ths and 16ths on one side, 32nds and 64ths on the other. But Gladstone’s square has a metric scale instead of 64ths. And a 12" blade is it; longer blades aren’t available. Highland Woodworking’s square is only available as a four-piece set. Its protractor head is nonreversible.
Though the heads are cast-iron and the blades nicely machined, there’s evidence of skimping on the details. The blades all were 5/64" thick, a 64th shy of the thickness of premium ones. Because the heads are nicely machined for the blade’s thickness, you can’t The easy, reliable adjustability of the premium squares is missing, too. With most top-end squares, you can slip the blade from the head, rotate the lock-bolt without even looking at what you’re doing, roll the blade over, and reinsert it. Just that quickly. Because the process is quick and reliable, you’re inclined to take advantage of this feature regularly. And the accuracy of your layout work improves as a result.
What I found with the in-betweeners was that I had to pay attention to what I was doing to reorient the blade. Even then, I had trouble with the Highland square.
My Final Analysis
Delving into combination squares has been worthwhile; I learned a lot of practical stuff. Knowing what you are getting is a significant factor in building a functional, sensible, practical tool collection ... and doing it economically. Essential criteria in selecting a combination square are:
- Ease of use
The low-end squares I sampled aren’t bad at all. They’re certainly economical. If your budget is really tight, look closely at as many different brands as you can before buying. Check its accuracy first thing, and return it if it’s out. Buying a second square with the longer blade is worth consideration too.
The high-end squares do meet all the criteria, but cost inevitably is a factor. If you aspire to the best, shop online and price the tool you want from makers like PEC, Mitutoyo and SPI to see if you can get a price that better fits your budget.
Don’t reject the in-betweeners. Those I sampled are accurate, quite versatile, and reasonably easy to use. If you can’t handle the tool before the purchase, just be sure you can return it. Again, check its accuracy first thing, and return it if it’s out. But also try removing, turning and reinserting the blade. If it isn’t easy, if you can’t do it repeatedly without a hitch, consider returning for a different design.
In the end, I’m comfortable with my $250 investment in combination squares. I knew enough to buy a good brand of square, but I had no idea of the choices available. I would have opted for the glare-free satin chrome finish on the blade. And I’m thinking seriously about getting a 36" blade for laying out sheet goods and large panels.