This mechanism consists of a base with two slots intersecting at right angles. Two sliders are confined within the slots and are attached to a handle by pivots (screws) at fixed positions along the handle. The mechanism can be used for drawing a perfect ellipse. This is done by positioning a writing utensil at the end of the handle while making a full revolution. For more information/history, see here.

With that said, it is often sold in novelty shops with interesting names like Bullsh*t Grinder, Bullsh*t Masher or Do-Nothing Machine. Interestingly, most of the names are preceded with state names such as Arkansas, Kentucky, etc. I guess that’s how locals make fun of their neighbors.

I made two versions of the Trammel. The first version is made from wood. This build is similar to LeumasYrrep’s version as shown here. I decided to take a different approach by making the slides from dowels instead of the layered approach. The second version is a 3D print. I’ve included all STL files in case you would like to print your own. The wood version was made from scrap wood; so my cost was minimal. The 3D printed version cost ~ $15 at my local library. The library charges $0.25/gram so I tried to reduce the weight by removing the four corners. I feel I could have reduced the weight by another 25% with a little more CAD work. If anyone is interested, I’ve also included STP files which can be modified or scaled in most CAD packages.

Trammel in Motion.

This video shows the actual build which should help in conjunction with the build instructions.