Sheet metal mark out or layout is the practice of putting dimensions on a piece of metal to show locations of cuts and bends that will be used to fabricate the final work piece. Sheet metal layout tools are needed to measure, mark dimensions, draw straight lines, find non-standard points and calculate round dimensions.
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Accurate measuring is an important part of sheet metal layout. Projects can require final dimensions that have a 1/32nd of an inch tolerance, which does not leave much room for error.
The standard measuring tools for sheet metal layout are a tape measure, circumference rule and dividers. Tape measures are used for measuring larger spans. A circumference rule of at least 3 feet is needed to make precise measurements and calculate round pipe circumferences at a glance.
Dividers have no numbers and are not classified as a measuring tool by many construction workers, but they are to a sheet metal worker. Dividers are used to transpose lengths during radial line development, determine radius points on an ogee duct fitting and bisect circles to determine equal lengths.
Measuring would have no effect if you did not have a way to place a mark on the metal's surface. Markers can be used, but the thick felt tip can be as larger as 1/8th of an inch and allows a lot of room for error. Markers are better left for marking piece numbers or circling bend and cut points.
A scribe or awl is used to lay line tight marks and lines on sheet metal. The awl's point is sharp and can be made of carbide, which is hard and allows the awl to retain its point longer.
Squares and Angle Finders
Squares and angle finders are important tools that can easily be overlooked when setting-up a mark out tool set. With squares you get what you pay for. Cheaper combination squares can often be out-of-square 1/16th of an inch or more in 12 inches. It is worth the money to invest in a trued square.
Framing squares have uses that go beyond standard layout, but are important as a time saver when you are marking 90 degree corners on sheet metal.
An angle finder used for sheet metal mark out is different then the standard protractors used in schools. The angle finder is composed of a block that has degrees marked in a half circle and an arm that rides on the metal. Angle finder's can accurately determine angles from 0 to 180 degrees.
A centre punch is used to place a round dimple on the area where a bend or hole will be placed in the sheet metal. The centre punch mark is easy to see at the brake and reduces the amount of walk from a drill bit when drilling a hole.
Uncommon tools used in sheet metal mark out are a flexible magnetic rule and trammel points. Trammel points are two sharpened rods that clamp to a metal bar or pipe to create larger radius arcs. They may not be used frequently, but when they are needed you will be glad you have them.
Flexible magnetic rules are used to make marking circumferences on sheet metal easier and more accurate.