Speed square
From Wikipedia, the free encyclopedia
A speed square is a three-sided, triangular shaped measuring tool manufactured by Swanson Tool Co., Inc. that is used to draw perpendicular lines on boards to be cut or to lay out angles for roofs, stairways, decks and other general construction. Another name is a 'rafter angle square'; it's marked with degree gradations for fast layout. The square's small size makes it easy to store and transport.
[edit] Specific uses of Square
It 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 to mention a few uses. It serves as a convenient straightedge and guide for circular saws and should be clamped when cutting splayed angles for user safety.
[edit] Operation of Square
The square consists of three Parallel (geometry) lines 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.
