A speed square, also called a rafter square, rafter angle square, and triangle square, is a multi-purpose triangular carpenters' tool used for marking out. Its functions include many of those of a combination square, try square, and framing square. Carpenters use it to make basic measurements and mark lines on dimensional lumber, and as a saw guide for short 45 and 90 degree cuts.
The term "speed square" is a genericised trademark based on those owned by Swanson Tool Company[1][2] which first manufactured and sold the tool.
History
Albert J. Swanson invented the A Speed Square in 1925 as a carpenter's layout tool. He later founded Swanson Tool Company to produce it.[3] Today, Swanson Tool Company still manufactures and distributes the Speed Square and other carpentry tools from its headquarters in Frankfort, Illinois.
Design
Speed squares are manufactured from a variety of materials such as aluminum, steel, and composites such as HDPE. They are also made in several sizes, including 7-inch, 8-inch, 25-cm and 12-inch sizes.
Embedded degree gradations on the tool eliminate the need for trigonometric calculations and allow for lines to be more easily made.
The tool is an isoscelesright triangle with a ruler on one equal side and a fence on the other. It is marked with the word Pivot at the right angle point and displays Degrees on its hypotenuse, Common and Hip/Val markings on its midsection.
Degree indicates the angle in degrees from 0° to 90°.
Common indicates the rise in inches over a 12 inch run for common rafters from 1 inch to 30 inch.
Hip/Val indicates the rise in inches over a 17 inch run for hip or valley rafters from 1 inch to 30 inch.
Some models have divots for fitting a writing utensil to mark lumber with. Speed squares made by the Swanson Tool Company also have a diamond shape cutout on the ruler side at 3½ inches.
Common lines made using a speed square include perpendicular cut marks and Angles definition of an angle for roofs, stairways, and decks.
The tool uses a 0° reference. This means when a board is squared off the tool reads 0°. The angle derived is actually a complementary angle, for example a 22.5° angle is actually 67.5°. The sum of the angles equals 90 degrees (22.5° +67.5°= 90°). It is also obvious from a visual check when using a protractor that where the instruments displays 22.5° is actually 67.5° on the protractor. Many newer slide miters and miter boxes display both angles. Some of the new calculators have a 0° and a 90° references. The only true angle is 45° on the triangular square. This can create confusion if the user does not understand this angular calibration when using trigonometric functions. The FIRST image below shows ⊾ P = 20° on the protractor and ⊾ T = 20° on the angle Square. The only similarity is that both of the angles are acute angle and complimentary. When the image is enlarged the protractor is on the ⊾ 20° index and the body rests on the edged face of the 2X4. The square is pivoted on the (left side 2x4) and locked into the ⊾ 20° degree index at the red marked line. The SECOND image displays ⊾ X = 70° on the clear protractor that is graduated in 360°, ⊾ X = 20° on the Aluminum angle square. Both red lines ⊾ X are Parallel and thereby congruent. "Postulate 4.1 (P 64)" congruent angle *ISBN978-0-7641-3918-5
^"Trademark Status & Document Retrieval". United States Patent and Trademark Office. May 19, 2017. Retrieved 2021-05-01. Mark: SPEED SQUARE [...] Goods and Services [...] For: Hand tools, namely, squares [...] Owner name: Swanson Tool Company, Inc.
^"Trademark Status & Document Retrieval". United States Patent and Trademark Office. May 19, 2017. Retrieved 2021-05-01. Mark: SPEED [...] Goods and Services [...] For: HAND TOOLS, NAMELY; SQUARES [...] Owner name: SWANSON TOOL CO., INC.