How To Make Straight Cuts With A Circular Saw and Speed Square

Learn How to Make Straight Cuts with a Circular Saw and Speed Square for Quick Accuracy

Looking for more accurate crosscuts and miter cuts but don’t want to fork out the cash for a miter saw or a track saw? Here’s a quick tip for how to make straight cuts with a circular saw and speed square.

Want more detailed video instruction? We have it for you on YouTube!

What You’ll Need

Circular Saw
Rafter Square (Speed Square)
Tape Measure
Pencil or Pen

How to Make a Straight Cut with Circular Saw and Speed Square

If you don’t have a trailer full of professional-level tools, you can still make perfect 90° and 45° cuts in lumber without a lot of extra expense. All you need is a circular saw and a speed square along with a tape measure and pencil.

Know the Lingo: “Speed square” and a “rafter square” refer to the same tool. Swanson made the rafter square famous and many folks call all rafter squares by Swanson’s trademark name, Speed Square. We use them interchangeably in this article.

Setup

Start by measuring out where you want to make the cut and use a pencil to mark it. For a 90° cut, it can be anywhere on the width of the board. For a straight 45° cut with a circular saw and speed square, you can mark either the longer or shorter edge. It depends on what you’re building, but we almost always mark the longer measurement.

Even before the saw comes out, your rafter square is going to help you make a more accurate cut by acting as a straight edge for you to mark against. A 90° cross cut is pretty straightforward—just line it up and draw a line directly through your mark.

For a 45° miter, keep in mind whether you marked the short end or the long end. If you notice that the square’s angle is going in the wrong direction, just flip it over to get it right.

Make the Cut

Now that you have perfect marks, you can make the cut freehand if you like, but using the rafter square as a guide will make it the most accurate.

How to Make Straight Cuts with a Circular Saw and Speed Square

You need to account for the offset of your circular saw shoe. The easiest way is to simply set the square on the board, place the saw’s shoe against it, and then slide both pieces until your blade lines up with your cut line.

Holding the square firmly in place with one hand, pull the saw back just a hair so the blade isn’t touching the wood, pull the trigger, let the blade spin up to full speed, and make your cut as you apply light pressure against the square to keep the saw on track.

A Few Things to Think About

Depending on whether your saw is blade-right or blade-left and how you’re most comfortable cutting, you may run into an issue where the motor housing hits your square. For most saws, you just need to adjust the blade depth shallower and you’ll clear it while still making a complete cut.

There are some limitations to this cutting method, though. Number one is that you can only make 90° and 45° cuts. There are plenty of other common miter angles that you can’t do the same way. You can mark other angles accurately with your square, it’s just much harder to hold the square securely without it shifting while you cut.

Then there’s the cutting depth. Most 7 1/4-inch circular saws will let you cut up to 2 1/2 inches deep—enough to get you through 2x material. Even 6 1/2-inch models will make that cut. While there are a few high-capacity circular saws that will cut 4x in one pass, it’s not something most DIYers are going to have on hand. You also want to keep both hands on those bigger saws!

Finally, there’s the size of the speed square itself. A typical 7-inch square can help you make both cuts on boards up to 2 x 8 lumber while a 12-inch rafter square can handle the entire range up to 2 x 12. It’s beneficial to have both sizes and you can get 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!