Trammels - Methods and Tips for Use
By John de Marchi

About four or five years ago I realized that I could increase the usefulness of the ruler stops by the addition of some accurately located points. The ruler stops had now been transformed into an additional function, direct reading Trammel Points.

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The trammel points are used like large dividers, to measure length, increments, but mostly to scribe arcs and circles. They are very useful for any type of geometric layout to generate hexagons, octagons and many types of geometric forms, or to locate points in space and to divide lines and angles with great accuracy. Because the trammels are mounted on a stiff ruler whose size can range from 12” to 24” they are easy to use and have none of that troublesome spring that frequently occurs with dividers. The points are tungsten carbide and they are very hard and also brittle, use a diamond hone to sharpen the points. When not in use, the points should be reversed to protect them and keep the user from getting stabbed. When in use, the points should be adjusted to extend the same length away from the trammel body, the same is true when using a pencil with the trammel pencil holder .


To generate a circle of a particular size, set the first trammel flush with the end of the ruler. Take the second trammel and move it so the inside edge reads the radius of the circle to be scribed. For example, if the diameter of the circle were 6”, the radius would be 3”, and the second trammel's inside edge would be placed on the 3” mark. Next, place the 60-degree or blunt point at the center of the circle, and use the very sharp point to then scribe a mark. Use light pressure to scribe, and if a deeper mark is desired, make several passes rather than one heavy pass that will tear up many materials.


To scribe a very sharp line in wood grain, use the optional knife blade which will cut cleanly with and against the grain. It is also very effective for slicing paper and thin films very cleanly. If you desire a pencil line, an optional pencil attachment is available which will hold a standard hexagonal wood pencil, but this is not a direct reading device. Mark the start point and end point of the desired length and adjust the trammel pencil holder to those marks, and draw a perfect circle or arc.

Another useful and handy device for use with the Trammels is the Slider-Coupler . This is used to couple two rulers together, thereby extending their length and the size of the arc that can be created with the trammels . The other use of the slider-coupler is to be able to take direct readings of interior spaces, such as the inside of a drawer or box over 12.5” in interior width. In use, the slider-coupler is mounted flush with the end of the ruler and locked in place with the two setscrews. Another ruler is placed in the adjoining slot, and the second ruler is moved until it contacts the opposite side of the object being measured. With both ends of the rulers touching the opposite ends, the thumbscrew can be locked and the rulers withdrawn to reveal the inside, direct measurement which would be 12” plus the measurements that the second ruler is extended.

The trammels, along with the pencil attachment and a framing square or similar right angle square of suitable size, can be used to generate very accurate ovals to specific dimensions of length and width. In use, one trammel with the point reversed to expose a smooth 1/8” dowel is set flush with the ruler. The second trammel, with the point reversed, is set to the radius of the short side of the oval, plus 1/16” to compensate for the radius of the 1/8” pin. The pencil holder is then set to the radius of the long side of the oval, plus 1/16. Using a square as a guide, the pins are placed, one at the apex of the square, and the other along one side of one leg. While keeping both pins of the trammels in contact with the sides of the square, the pin at the apex is moved along down the leg while the other pin is moved towards the apex with the result that the pencil will draw a perfect quarter pattern for the oval. The pattern produced will be accurate and to size, without using any complex systems or calculations. Because all the parts are inflexible, the pattern will be crisp and sharp.


Trammels can also be used to mark off increments of distance easily. The first trammel is set flush to the ruler end and the second trammel to the distance required and then locked in place. The trammels and ruler are then walked along a line or curve from point to point and swung from one point to the next, making for a very accurate increment of distance layout.


By using some basic geometry, a line can be divided equally, a true vertical can be established, and any angle can be divided equally to determine a miter angle. Many angles and geometric forms can be generated quickly and easily with such a solid and easily adjustable set of trammels.

Copyright © 2003 by John de Marchi