Speed square
From Wikipedia, the free encyclopedia
The Speed Square is a three-sided, triangular shaped measuring tool, manufactured by Swanson Tool Co., Inc., that can be used to draw perpendicular lines on boards to be cut or to lay out angles for roofs, stairways, decks and other general construction. The tool is marked with degree gradations for fast layout and cutting of lumber without performing angle calculations. The Speed Square was invented in 1925 by Albert J. Swanson and has become a generic name for the family of triangular squares with pre-calculated markings. These tools are also called by their generic names, "rafter angle square". Modern Swanson Speed Squares can be differentiated from other rafter angle squares by their diamond shape cutout at the 3 1/2 inch mark.
[edit] Anatomy and uses of the Speed Square
Swanson Co. advertises that the Speed Square can be used as a, "Try Square, Miter Square, Protractor, Line Scriber, & Saw Guide". The tool is shaped in an isosceles triangle and is marked with the "Pivot" point, Degrees (angle from 0 to 90), Common (rise over 12 inch), Hip and Valleys (rise against angle), a ruler, and some may have divots for fitting a writing utensil to mark lumber with.
The Speed Square is used to cut Common, Hip, Valley and Hip or Valley Jack rafters, layout stringer in stair fabrication, mark angles, determine angles, and to square off boards. It serves as a convenient straightedge and guide for circular saws (professionals recommend that the square be clamped when cutting splayed angles for safety).
[edit] Operation of the Speed Square
The original Swanson Speed Square is famous for its "Little Blue Book" that accompanies the tool. The book describes uses and methods for maximizing the utility of the tool. Most generic versions of the tool do not come with any instructions.
The square consists of three parallel lines to its hypotenuse with markings on them. There is a degree line with increments of 1°, There are a common, and a hip-valley lines in increments of a one pitch to a 30 pitch. The intersection of the pivot point (located @ the tip of the 90° angle on the square) and where the readings coincide on the edge of the board determines the pitch or angle. The 12 inch square can be used to lay out stairs. This tool uses a 0 degree 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° (22.5° +67.5° = 90°). It is obvious from a visual check that where the instruments displays 22.5° is not 22.5°. Many of the new slide miters and miter boxes display both angles. Some of the new calculators have a 0° and a 90° references to do angular calculations. This can create much confusion if it is not clearly understood.
