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A beam compass allows people to draw circles much larger than would be possible with a conventional compass design. It can be used in woodworking, engineering, construction, and similar activities. Manufacturers produce a range of designs and it is also possible to make one on the spot for a given project, using some basic tools that should already be available. In addition to being used for drawing circles, the beam compass can also be used for arcs, straight lines, and measurements.
This tool consists of a beam with a set of moving sockets that can be adjusted along its length. In a homemade version, a woodworker may do something like using a dowel as a beam, and clamping pins or pencils to the desired points. Commercially produced beam compasses can use lengths of wood or metal with adjustable pins. In all cases, the pins lock in place so they will remain at a fixed distance while the instrument is in use.
Some beam compass designs use adjustable stiffened measuring tapes. These allow users to set the tape at the desired length, using a pen or pencil at the end as one point of the instrument. A ruler can also be used as the beam. The best option can depend on the types of projects someone makes, and the level of precision needed with measurements. People who work with large circles may find the beam compass faster and more practical to use than other designs, which can get quite large and cumbersome to accommodate a big diameter.
Like other tools used in construction, drafting, and related activities, a beam compass can develop wear and tear over time. It should be appropriately stored between uses to prevent rusting and warping. Periodic cleaning and oiling can ensure that it locks tightly and will not slip during use. Some beam compasses come with cases for protection, and it is also possible to make one to shield the instrument from damage.
To draw a circle with the beam compass, one point is fixed at the middle while the other is rotated around it. This can be done with a sharp instrument to cut out a circle, a tactic that can be used for projects where people need to quickly cut perfectly round circles. Arcs can be drawn by dragging the compass only partially through the circle. Lines can be made from the edges of a project by using one end as an anchor point.