Learn how to make straight cuts with a circular saw and Speed Square for fast accuracy
Looking for more accurate cross and miter cuts, but don't want to spend the money on a miter or track saw? Here's a quick tip on how to make straight cuts with a circular saw and a speed square.
Want more detailed video tutorials? We've got it for you on YouTube!
what do you need
- circular saw
- Rafter Square (Speed Square)
- tape measure
- pencil or pen
If you don't have a trailer full of pro-grade tools, you can still make perfect 90° and 45° cuts in wood without spending a lot of extra money. All you need is a circular saw and a speedometer along with tape measure and pencil.
Know the terms: "Speed square" and "raft square" refer to the same tool. Swanson made rafter squares famous and many refer to all rafter squares by Swanson's trade name, Speed Square. We use them interchangeably in this article.
First measure out where you want to cut and mark with a pencil. For 90° cuts it can be anywhere across the width of the board. For straight 45° cuts with a circular saw and speed square, you can mark longer or shorter edges. It depends on what you're building, but we almost always mark the longer measurements.
Even before the saw comes out, your rafter square will serve as your marked straight edge to help you make more accurate cuts. A 90° crosscut is easy – just line it up and draw a line directly across your mark.
For 45° miters, remember whether you marked the short or long end. If you notice that the corners of the square are oriented the wrong way, just flip it over.
Make a decision
Now that you have the perfect marks, you can freehand cut if you want, but using the rafters as a guide will make it most accurate.
You need to account for the offset of your circular saw shoe. The easiest way to do this is to simply place the square on the board, place the saw shoe against it, and slide the two pieces until the blade is aligned with the cut line.
Hold the block firmly in place with one hand, pull the saw back a bit so the blade does not touch the wood, pull the trigger, let the blade spin at full speed, and cut while applying light pressure to keep the saw on track on the square.
a few things to consider
Depending on whether your saw is right or left bladed and how you are most comfortable cutting, you may have issues with the motor housing hitting your block. With most saws, you'll just need to set the blade depth a little shallower to clear it while making a full cut.
However, this cutting method has some limitations. First, you can only make 90° and 45° cuts. There are plenty of other common miter angles that you can't do in the same way. You can accurately mark other angles with your square, it's just harder to hold the square firmly without moving it as you cut.
Then there is the depth of cut. Most 7 1/4-inch circular saws can cut up to 2 1/2 inches deep—enough to cut twice as much material. Even the 6 1/2-inch models can do this. While there are some high-capacity circular saws that can cut 4x at a time, most DIYers don't have that on hand. You'll also want to keep your hands on those bigger saws!
Finally, there is the size of the speed cube itself. A typical 7" square will help you make two cuts on boards up to 2 x 8, while a 12" rafter square will handle the entire range up to 2 x 12. Having both sizes is beneficial and you can get good quality ones like the ones we used for less than $20 each.
If you have any questions or feedback feel free to leave them in the comments below, and as always, thanks for reading!
Want to learn more about the tools we used in this article? Click on the title to read our review or click the button to buy it for yourself!