marking gauge
A marking gauge is used in woodworking and metalworking to mark out lines for cutting or other operations. In metalworking it can be known as a scratch gauge. The purpose of the gauge is to scribe a line parallel to a reference edge or surface. It is used in joinery and sheetmetal operations.
The gauge consists of a beam, a headstock, and a scribing or marking implement, typically a pin, knife, pen or wheel. The headstock slides along the beam, and is locked in place by various means: a locking screw, cam lever, or a wedge. The marking implement is fixed to one end of the beam.
Next the user measures the desired distance from the edge of the wood. The headstock is set so that the distance between it and the marking implement equals the distance from the reference edge to the line to be scribed. The user then holds the headstock tightly against the reference edge or surface and draws the gauge along so that the headstock follows the reference edge, and the marking implement, in contact with the surface to be marked, scribes a line of the desired length.
The marking implement is chosen depending upon the operation to be performed. Some marking gauges have the capability to allow a number of implements to be fitted, others do not; and a woodworker will often have a number of different types. A steel pin is used when scribing with the grain. A steel knife is used when scribing across the grain. The pen or pencil is used when the woodworker does not wish the surface to be marred. Generally speaking, the pin and knife yield more accurate marking than do the pen or pencil.
The style of gauge which uses a knife instead of a pin is often described as a cutting gauge. Other variations include a panel gauge which has a longer beam and larger headstock for scribing lines that are further from the reference edge. A mortise gauge has two pins that can be adjusted relative to each other at the end of the beam. This gauge is used to scribe two parallel lines simultaneously and is most commonly used to layout for mortise and tenon joinery. The marking gauge is a replacement of of the steel rule and pen.
References
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