Trammel Points - Overgrown Dividers

Trammel points or beam compasses are typically used to measure distances between points or scribe a circle that is beyond the reach of the legs of large dividers. They are used in conjunction with a beam to which they attach that can be of any length. Collecting trammels is a focus unto itself, but since they are related to dividers, the primary focus of this blog, I’ll mention a few variations from my limited collection.

The earliest trammels were likely made of wood and clamped onto a wooden beam which might be graduated or unmarked. One trammel head was usually fixed in place at the end of the beam while the other could slide along the beam a desired distance and be clamped in place with a thumb screw. The tips of the trammel heads were sharp metal points. These wooden tools were typically craftsman-made.

                                                                             

Two head wooden beam compass on a 32" beam with fine adjustment

 

                                                                        

Three head wooden beam compass on 28" beam; possibly for making elipses?

Nineteenth century and earlier cast brass trammel heads with steel points are often ornate and finely crafted, much in the manner of fancy plumb bobs. They are often attached to a short piece of wood, the keeper, separate from the beam. This makes them very portable, as a beam was often fashioned when needed out of scrap wood. One of the pair of trammel heads often provided a means for attaching a pencil or other marking device. There is often a brass shoe under the attachment screw which presses on the beam (below left). This piece is easily lost.

                                                                        

           Left: Unmarked, likely Edward Preston, Birmingham, England.    Right:: Marked "Bumidge"                                   

  

Machinist's and architect’s beam compasses were offered by all the major machine tool companies and can be quite complex with a fine adjustment mechanism and exchangeable points that allowed them to be used for large-scale outside and inside measurements beyond the reach of calipers. Some, such as those offered by Stanley, could be attached to straight or folding rules.

         

Left: Dietzgen #646, unmarked    Right: L.S. Starrett #89A, with cone center and coupling.