Machine Shop : Common Layout Tools
**Scriber ** To obtain an accurate layout, fine lines must be scribed in the metal. A scriber is the layout tool that is used to produce these lines. The point is made of hardened steel and is kept chain by honing on an oil stone. A tungsten carbide marker is used to lay out lines on glass, hardened steel or other hard materials.
**Divider ** When laying out circles, arcs, and radii, it is best to use the divider. The legs of the divider must be of the same length and be kept sharp. The divider cart be used to lay out and measure distances. To set the divider to the correct length, place one point on an inch mark of a steel rule and open the divider until the other leg matches the correct measure-merit required.
**Trammel ** When scribing circles, arcs, and radii that are too large to be produced with the divider, a trammel should be used. The trammel is made of three main parts: the beam, two sliding heads with scriber points, and an adjusting screw that is attached to one of the heads. The trammel can be made to scribe larger distances with the use of extension rods. This layout tool is set in the same manner as the divider.
**Hermaphrodite Caliper ** The hermaphrodite caliper is a tool used to layout lines that are parallel with the edges of the workpiece. It can also be used to locate the center of cylindrical shaped workpieces .
Surface Gage The surface gauge is used for many purposes, but is most often used for layout work. The gauge can be used to scribe layout lines at any given distance parallel to the work surface. The spindle may be adjusted to any position with respect to the base and tightened in place with the spindle nut. The rocker adjusting screw provides for finer adjustment of the spindle by pivoting the spindle rocker bracket. The scriber can be positioned at any height and in any desired direction on the spindle by adjusting the scriber. A surface plate and combination square are needed to set the surface gauge to the correct dimension.
**Surface Plate ** A surface plate provides a true, smooth, plane surface. It is used in conjunction with surface and height gauges as a level base on which the gauges and the workpiece are placed to obtain accurate measurements. These plates are made of semi-steel or granite and should never be used for any job that would scratch or nick the surface.
**Vernier Height Gauge ** The vernier height gauge is a caliper with a special foot block to adapt it for use on a surface plate. Height gauges are available in several sizes: the most common are the 10, 18, and 24 inch gauges in English measure and the 25 and 46 cm gauges in metric measure. Like the vernier caliper, these height gauges are graduated in divisions of 0.025 inch and a vernier scale of 25 units for reading measurements to thousandths of an inch. Always be sure the bottom of the foot block is clean and free from burrs.
Combination Square Set The combination square set is used for layout operations. The set consists of a blade(graduated rule), square head, protractor, and center head.
**Blade ** The blade is designed to allow the different heads to slide along the blade and be clamped at any desired location. The groove in the blade is concave to eliminate dirt buildup and permit a free and easy slide for the heads. By removing all the heads, the blade may be used alone as a rule.
**Square Head ** The square head is designed with a 45° and 90° edge, which makes it possible to be used as a try square and miter square. By extending the blade below the square, it can be used as a depth rule. The square head can also be used as a level.
**Protractor Head ** The protractor head is equipped with a revolving turret graduated in degrees from 0 to 180 or to 90 in either direction. It is used to measure or lay out angles to an accuracy of 1°.
Center Head The center head, when inserted on the blade, is used to locate and lay out the center of cylindrical workplaces.
**Bevel Protractor **
The bevel protractor consists of an adjustable blade with a graduated dial. The blade is usually 12 inches long and 1/16 inch thick. The dial is graduated in degrees through a complete circle of 360°. The most common use for this tool is laying out precision angles. The vernier scale is used for accurate angle adjustments and is accurate to 5 minutes or 1/12°.
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