Let's go ahead and get this out of the way. The Swanson Tool Company (link) invented the term Speed Square and built the first tool of its kind. Although they don't like people using the term in general terms, it's too late. The name is a lot like Kleenex or Sawzall. Technically these tools are called raft squares, or some people call them triangular squares. Most people call them "speed squares" (lower case), though. We will also use that vernacular in this article. There are many tricks to using speed cubes. Apart from laying the roof rafters, here are just the most important parts. This is beyond the scope of this article.
Table of contents
- Types of speed cubes
- 1. How to use a velocity square as a protractor
- 2. Setting the Miter Saw Angle
- 3. How to make a straight cut with the speed gauge as a guide
- 4. Use the Speed Square to mount the blade on your table or circular saw
- 5. Use a Speed Square as a Scale
- 6. Use a speedometer as an altimeter
- 7. Using the Speed Square as a spirit level
- Other markings on speed squares
- in conclusion
Types of speed cubes
Speed cubes are usually made of plastic or aluminum. Plastic's light weight and high visibility. They don't last as long as those made of aluminum. Plastic speed squares are non-destructive and ideal for use on painted surfaces such as siding.
For a few bucks more, you can get aluminum speed cubes. These are really something you will never forget. Swanson made the original, but Irwin made one that's perfect for those with poor vision or dark conditions. The beautiful Milwaukee rafter squares are very accurate and they also make a 4 -1/2" trim square which I especially like when working with 2×4's. Many companies make 12-inch models. I use this size most often as a saw guide – more on that later.
Husky and Crescent made a 6-inch triangular square they call a 2-in-1 expandable layout tool. This rafter square with extension arms can be flipped over to extend up to 12 inches. They look identical except for the color. I bought one and it's 1/64" off. Open or closed, it's still irregular. I've read the reviews on Amazon, and a few others have reported that their reviews are also sloppy.
1. How to use a velocity square as a protractor
The most obvious use of speed squares is to mark 90 degrees and 45 degrees. The speed cube is actually a protractor. However, a protractor and a velocity square measure angles slightly differently. Check out the photos below. Using a protractor, 0 degrees is horizontal and 90 degrees is vertical. For velocity squares, 0 degrees is vertical. To solve this problem, we use a quick workaround.
To use the rafter square as a standard protractor, simply rotate the tool until the indicated angle equals whatever measurement you need to subtract from 90. This means that if you need a 60 degree angle as shown below, use a 30 degree angle on the rafter square.
2. Setting the Miter Saw Angle
Now you may be asking yourself, "Why do I have to do this math?" Good news! When it comes to cutting boards, you don't. The angle on the speed square matches the angle on the miter saw – this is also based on 0 degrees vertical. So a 30 degree cut on a miter saw is just a 30 degree line on a speed square. Do your markings, then do your cutting.
3. How to make a straight cut with the speed gauge as a guide
In my opinion, perhaps the most important use of the speed cube is to help you make straight cuts. To use the speed square as a sawing guide, start by marking the lines you intend to cut on the board at 90 or 45 degree angles. Now position the saw so that the teeth line up with the cut line. Place the speed square against the saw shoe as shown in the picture to act as a fence. Make sure the space between the saw blade and the cutting line is consistent.
While the 6" model works fine for this, I prefer to use the 12" speed cubes. The extra length gives the saw more fence to ride against.
4. Use the Speed Square to mount the blade on your table or circular saw
Place the square on the saw, T-side down, so it is free standing. Now, raise the table saw blade all the way up and angle it to match the triangle square if a 45 or 90 degree angle cut is required. We also use squares to make sure our table saw fence is square. Finally, you can adjust your circular saw the same way you would with a table saw blade.
5. Use a Speed Square as a Scale
Many rafter blocks have a series of jagged notches. They are designed so that you can place a pencil in them and draw a line on the board at a set distance. The chevron acts as a guide for your pencil as you slide the square down onto the board. Just hold the fence of the speed block tightly against the wood when moving.
6. Use a speedometer as an altimeter
Your speed gauge serves as an excellent blade height gauge for your table saw or milling machine table. Some blocks are not marked finely enough to be very accurate. Others, like the one from Milwaukee, are pretty precise. To use this method, stand the square on its T-shaped edge so it is free standing. Use the scale on the 90 degree side of the triangle to adjust the height of the blade or bit.
7. Using the Speed Square as a spirit level
In a pinch, you can use the cube as a level. All you need is a plumb bob or a piece of rope with a weight on it. One nut will do. Place the plumb rope at the pivot point with the widest part of the triangle facing down. When the rope is at 45 degrees, the triangle will be horizontal.
Other markings on speed squares
A standout feature of the original Swanson Speed Square design was the addition of jack, valley and hip rafter scales. Each of Square's brands tries to put its own stamp on it, to make its own improvements. My Swanson is so old it doesn't have the notches for the marking gauge. Another company added, and then Swanson added it to their product. Some companies put common rafter conversion tables on their speed squares.
One of the most unique places is Milwaukee. It has a rectangular opening and is designed to be used as a saw frame for cutting pipes. Slide the end of the pipe over the rectangle and place the speed block on the ground, it will hold the pipe up as you make the cut. Eventually, this can damage the long side of the square as it bounces around and creates nicks and chips in it. I'd probably avoid using this too often and buy a real bracket like this one, which also attaches to 2x4s.
Adjust the speed block
Fortunately, I was able to bring the square back to 90 degrees with a file. Here's a quick tip – aluminum can clog files very quickly. Chalk the file before filing the aluminum, it will act as a lubricant and prevent clogging. If you're not comfortable with your file-handling skills, stick a sheet of sandpaper to your workbench. You can then move the speed square back and forth across the sandpaper, applying more pressure on the side that needs to be removed to make it square.
Place the non-square, the square, and the known exact square back-to-back. You also want to have them all on a clean piece of flat glass. In my case, I used a freshly cleaned glass cooktop. Next, turn on the light behind the square. If the squares touch each other and light passes through, one of them is not a square. They are perfect squares if no light gets through.
Whether you call them speed cubes, rafter cubes, or triangular cubes, they get the job done just fine. This versatile tool has a place in any toolbox, even if you've never used it to build a roof. You may also want to check out our article on how to measure and mark wood with a tape measure.