The single most important thing in woodworking project success is an accurate measurement. “Measure twice, cut once” is more than just a cute saying in carpentry, and means a project is more than likely to turn out well for you.
Accuracy must be important both in measuring distance and in measuring angles. This refers to squares, and in particular combination squares. We’ve written about squares in an earlier piece, which you will find here.
In that piece, we wrote of try squares, framing squares, and speed squares, but it was the combo square that we especially lauded. We referred to it as the Swiss Army knife of squares because of the many things it can do for us in the shop.
For those who don’t know a combo square, it’s a ruler, called a “blade,” on which a piece called the “head” will slide along the blade to the desired measurement. The knob that holds the head to the blade is easily adjustable to move it along or tighten it for the measuring.
The head includes what is called the “anvil” that sits at a 90-degree angle to the blade, and a “shoulder” that sits at 45 degrees to the blade. These allow the square to measure, mark and verify both 90-degree and 45-degree angles, measure the center of any circular workpiece in your project, and measure depth and distance along the blade.
The head also includes a bubble vial. This can be used to measure level as you move along a workpiece edge or plate. With this feature, you won’t have to reach for another hand tool.
Today’s combination square was invented in the late 1870s by Laroy S. Starrett, and patented in 1879. One year later, he founded the L. S. Starrett Company in Athol, Massachusetts. Starrett originally designed the hand tool for machinists, but over time it became popular with woodworkers for all of the obvious reasons.
The Combination Square Blade
The rules, or blades, are made of stainless steel and usually with either a smooth or brushed finish.. Blades come in lengths ranging from 4” to 24”, with the 12” rule being the most common one found in woodworking shops. The rules will have a graduation scale and type in both inches and centimeters, one on either side.
The blade designation numbers will tell you about those graduated scales. For instance, the 4R graduation will be marked in 8ths and 16ths marked on one side, and 32nds and 64ths on the other. The 16R graduation will be broken down ever further, with 32nds and 64ths on one side, and 50ths and 100ths on the other.
For most woodworkers, the 4R is more than adequate.
There is so much more that a combination square will do for you, too. Measuring and marking a square cut line on a board, measuring and marking lines along the length of boards, measuring the square of a board edge after cutting, measuring the miter cut on a board or board edge, and more are all possible with a combination square.
The Combination Square Heads
The heads are either forged steel, cast iron, die-cast aluminum, or plastic. The aluminum heads are lighter and less expensive than the steel and iron, but can be less accurate over time as less durable.
The heads come in three models:
- Standard. This one is the one described earlier, with the anvil and the shoulder, as well as the bubble vial.
- Protractor. Exactly what it sounds like, it has an adjustable 180-degree protractor, sometimes called the turret. The turret has a graduated scale in both directions, allowing you to measure both the angle and its complement.
- Center Finder. This head has two faces that meet at 90 degrees, and when attached one edge of the blade will bisect the two faces at 45 degrees.
The most commonly used head is the standard head. Heads are interchangeable, and it is easy to swap one out for the other, but the standard head is, well, the standard most often used in woodworking shops. Heads are commonly painted with a black finish.
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The L. S. Starrett Company still operates today in Athol, Massachusetts . . . made in America.
If you want to see all that a combination square can do, here’s an excellent video to watch.
What Are The Starrett Square Choices
It is important to remember the extreme importance in accuracy of measurements for your project. Starrett squares are extremely accurate from the moment they are manufactured. They will run you double the cost of other combo squares from the big DIY stores, and those that have aluminum or plastic heads. The one thing they can’t measure for you, though, is the improved quality of your project results because of that accuracy.
We mentioned blade size earlier, and the first choice you’ll need to make for your shop is which size will suit most of your projects. While the 4” blade will fit easily into your tool kit or pocket, you’ll likely find it too small for most of your work.
A 12” blade is probably the most practical size to choose for general purpose use, and is the most common one found in workshops.
The next choice you will need to make is the head. Among the three choices, standard – protractor – center finder, the standard head is the one you’ll end up using most often.
However, these precision tools have interchangeable heads. This means you will need just the one blade, and can always grab one or both of the other heads with confidence knowing they will fit the blade you chose.
It will depend on what projects you are likely to be taking on in your shop. For instance, if your projects will include circular pieces of any kind, it will probably be necessary to find the centers, making the center finder head a good option to have handy.
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While the Starrett brand is not the only very good and highly accurate combination square brand on the market, it is the most well known brand for accuracy and quality manufacturing. At anywhere from 3 to 5 times more expensive than most other combo squares, though, some prefer to find a less expensive option.
Many woodworkers use the Stanley Rabone square with great satisfaction. It has a cast iron head and a hardened steel blade, and is a very reliable square. It is also much less expensive than Starrett models.
However, any woodworker who knows his squares will agree the Starrett combination square is the very best made square you can buy. Their quality and engineering standards are the highest in the industry, their squares are accurate right out of the box, and they maintain that accuracy for decades.
For most woodworkers, then, we would recommend a Starrett combination square with a 12’ blade and a 4R graduation scale. Add to it a standard head as the one you will most likely be using on your projects. If the budget allows, you could also pick up a center finder head if you think you’ll need to be finding the centers of circular pieces or dowels.
As for prices, our research tells us you should expect to pay somewhere between $90 and $150, depending on the merchant you purchase from, for a 12” 4R graduation scale model.
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However, if you really want to splurge, you could purchase a 4-piece set (12” blade and all three head styles) for between $275 and $350.
Yes, that’s a lot of money, but you do get what you pay for, and Starrett is considered the best made, most accurate, and longest-lasting combination square manufactured today. And again, it’s made in America.