Tool Tutorial: Speed Square

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Project theme:
Suitable for grades:
Tools & Materials
Material List
  • scrap lumber (eg, 2x4, 1x6 or similar)
  • Optional

  • tape measure
  • nail
  • 12" x 12" plywood
Tool list
  • Speed square (aka rafter square)
  • Pencil
  • Optional

  • Hammer

    Starting at Square One

  1. The word “square” is often used when describing 90° angles (also called "right" angles, when two lines or objects are perpendicular to each other). It can get tricky when you realize that the word "square" is used in many different ways! For example, “square” is a noun referring to an object with 4 equal sides and 90° corners. It can also be used as a verb, for example, when you “square” two pieces of wood, moving them until they are perpendicular (at a 90° angle) to each other. The word “square” can ALSO be an adjective, or a description of how two objects are positioned relative to each other, for example, you could say “the wall is square to the floor”. And then to top it off, this tool you are learning to use which is called a "square", is clearly a triangular shape! Read on to learn some of the amazing things this mysteriously named tool can help you do.
  2. Safety Considerations

  3. Speed squares, also called rafter squares, are very safe tools to use as they have no blades or moving parts. Try not to drop them, especially the metal ones, as it is possible to bend the edge which can result in your speed square giving you inaccurate readings and measurements.
  4. What's a Speed Square Used For?

  5. Speed squares are a great tool for your layout stages, making marking lumber quick and easy. You can use them to draw a 90° (“perpendicular”) line across a board at a pre-determined length along the wood. For example, when you need to cut then end off a board, you can measure the length you need with a tape measure and make a small pencil mark. Hook the flared edge of the speed square tightly to the side of your board and slide it until the straight side meets your mark. Drag your pencil down the edge of the speed square to draw your line.
  6. Speed squares also allow you to quickly mark a 45° line in the same way. Hold the flared edge securely on the side of your board and line up the angled side of the speed square at where you want your line. Drag your pencil along the edge of the speed square to draw your 45° line.
  7. You can use your speed square as a kind of protractor. If you have a custom angle that you need to mark or cut, place the edge of the speed square on your board and swing the speed square on the “pivot” corner at the 90° point. The numbers marked on the long side of the speed square represent degrees; if you need to mark a 30° line, match the 30 up to the edge of the wood, and mark the line with your pencil.
  8. Some speed squares have numbers on the edge that you can use as a ruler. Hook the flared edge on a board and measure down from the top in the same way you read a tape measure.
  9. A speed square can help you scribe a line (this means to draw a straight line parallel to the edge of the board a specific distance in). For example, if you need to scribe a line 2” in from the edge of your board, first clamp your wood to the work surface so it doesn’t move around. Place the speed square on the board edge, put your pencil in the 2” slot, then drag the speed square along the edge to scribe the line. Keep the flared edge of the speed square snug to the board as you move it along.
  10. Use your speed square to “check for square”. For example, you might want to check if a table saw blade is perpendicular, or “square to”, the table top before you make a cut.
  11. You can also use them to check for square when you are trying to make an object or building with perfectly 90° corners.
  12. Speed squares are also called “rafter squares”, because they can be used to mark where “birdsmouth” cuts need to be made on a rafter, a piece of wood that supports the roof of a building. A birdsmouth is a 90° notch cut out of the bottom edge of a rafter that allows it to sit snugly on the top of a building’s wall. The speed square can help you determine the angle of the roof and where to make your birdsmouth cuts; to learn how, ask a home builder or look up a detailed tutorial.
  13. Environmental Consideration

  14. Speed squares, if treated with care, can last for many decades! You can buy speed squares made of metal or plastic; both are durable and long-lasting. Keep in mind how long it takes plastics to break down in a landfill; if you break a plastic speed square, put it in the recycling.
Extension Challenges
  1. Practice using your new tool! Grab a 2x4 and mark and cut out a set of building blocks of different rectangular dimensions. Make triangular blocks by marking out 45°, 60°, and 30° angled cut marks. Cut the pieces with a hand saw, then sand them and finish them with a non-toxic, food-grade finish, such as cutting board wax.
  2. Walk around your school or home with your speed square to check corners for “square”. Are all the floors square to the walls? Are the walls square to each other? Can you find anywhere they are not square? Why might this be?
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