Trammel points
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Trammel points are a device that is commonly used to scribe a circle. Their relatively small size makes them easy to store or transport. Another advantage is that they are simple to use. They consist of two separate metal pieces (approx. 2.5" X 5" X 1/2") that are usually connected by a piece of wood.[1] There is also a trammel[2]not to be confused with trammel points. There are several different types of Trammel points but they all work on a similar principle. This process is also referred to as Beam-compass.
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[edit] Use in scribing a circle
The points are used to scribe a Circle. The size of the radius can be adjusted by sliding the metal across the wood(beam)and locking it by turning a knob at the desired location. The threaded machine rod is similar to the Bolt.The only limitation is the rigidity of the wood being used. Longer pieces tend to get floppier depending on the species of wood used. Metal can be used as an alternative but also has length limitations. Trammel points score a precise cut out line with the sharp point of the rod. . When the circular knob is turned, it micro adjusts the radius of the circle. The spring locks the mechanism at the precise desired location. Turning clockwise decreases the radius while turning counterclockwise increases the radius slightly.
[edit] Use in transferring measurements
Trammel points can also be used to make a series of repetitious measurements in a precise manner. Each point is rotated 180 Deg and this process is repeated until the desired measurement is reached. The indentation created by the sharp point of the trammel is easily seen and makes a precise point to reference off to the next location.
[edit] Footnotes
1. The wood timber is not included in the purchase of the trammel points. It can be ripped on a table saw. A lumber yard or woodworking store should have a piece readily available to fit the opening also.
2. The trammel is a mechanical device for circumscribing ellipses. This consists of a metal cross with grooves in it to allow one part of the compass to slide up and down and sideways and the other end of the compass draws the ellipse.
[edit] Variants
The Circle cutter is a basic variation of the beam compass. There are many types of circle cutters. This cutter is used primarily to score a circular pattern in the drywall in order to fit over recessed lighting in the ceiling. The tool consists of a square shank with a sliding pivot that is locked into the desired location with a turn knob. The shank is graduated into 16 units and each unit is further divided into increments of one quarter. One end of the shank has a fixed cutter wheel that scores a fine line in the drywall.
