A Trammel of Archimedes—also called an elliptic trammel or ellipsograph—draws an ellipse with a writing point attached to a bar. To make a basic version, guide two sliders along perpendicular tracks, connect them with a rigid bar, and attach a pencil to the bar. Moving the bar makes the sliders travel in their tracks while the pencil traces the curve.
What is a Trammel of Archimedes?
It is a mechanical ellipse-drawing tool. Two sliders move along tracks set at right angles to one another. A connecting rod or beam joins the sliders, and a writing point on the beam traces an ellipse as the assembly moves. The Smithsonian describes the mechanism as an elliptic trammel and documents its use for engineering drawings and blueprints. Smithsonian National Museum of American History: Keuffel and Esser Trammel
The tool is useful when a drawing needs an ellipse rather than a circle. The Smithsonian notes that a circle viewed at an angle appears elliptical, which is one reason ellipses arise in technical and architectural drawings. Smithsonian National Museum of American History: Ellipsographs
How do you make a basic trammel?
The essential layout is two perpendicular tracks, a slider in each track, a rigid bar connecting the sliders, and a pencil or other tracing point attached to the bar. The Science Museum Group describes the simplest form as two bars at right angles, blocks that slide in them, and an adjustably fixed rod with the tracing point at its outer end. Science Museum Group: Elliptic trammels by Shuttleworth
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- Set out the tracks: Arrange two straight tracks so they meet at a right angle. The sources describe the geometry but do not specify dimensions or construction tolerances.
- Fit one slider to each track: Each slider needs to travel along its track while remaining connected to the bar.
- Join the sliders with a rigid bar: The bar must keep the sliders linked as they move. Arrange their attachment points so their positions along the bar can be changed if you want to adjust the ellipse.
- Attach a writing point: Fit a pencil, lead holder, or other tracing point to the bar. The documented Keuffel and Esser instrument has an adjustable writing tip and a reversible pencil-lead holder. Smithsonian National Museum of American History: Keuffel and Esser Trammel
- Move the bar to draw: Keep the sliders in their tracks and guide the writing point across the drawing surface. Its path forms an ellipse.
This is a description of the mechanism, not a dimensioned construction plan. The cited museum descriptions do not establish preferred materials, a fastening method, or tolerances for a modern homemade tool.
How do you adjust the ellipse?
Change the sliders’ positions along the connecting beam. On the Keuffel and Esser instrument documented by the Smithsonian, bringing the sliders closer together makes the resulting ellipse more circular. The source does not give measurements for particular ellipse shapes, so set the positions by drawing and checking the curve you need rather than relying on a specified numeric ratio. Smithsonian National Museum of American History: Keuffel and Esser Trammel
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Should you build a trammel or use an ellipse template?
| Option | Adjustability | Simplicity and cost | Precision |
|---|---|---|---|
| Adjustable trammel | Slider positions can be changed to draw different ellipses. Smithsonian National Museum of American History | The cited sources do not state a comparative price or a preferred modern build method. | The Smithsonian notes that more elaborate ellipsographs are intended for more precise drawings, but supplies no quantified accuracy comparison. Smithsonian National Museum of American History |
| Static ellipse template | Draws one ellipse size. Smithsonian National Museum of American History | The Smithsonian says a template made from wood or plastic is easy and inexpensive to make. It does not give a price comparison with trammels. Smithsonian National Museum of American History | The cited source gives no quantified accuracy data. |
Choose a template for a single fixed curve when simplicity matters. Choose an adjustable trammel when you need to vary the ellipse; more elaborate ellipsographs are an option when drawing precision is the priority, although the cited source does not quantify the difference.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What does the name mean, and did Archimedes invent it?
“Trammel of Archimedes” is a familiar name for the device, alongside “elliptic trammel” and “ellipsograph.” The cited museum sources do not establish that Archimedes invented this exact mechanism, so the name should not be treated as proof of its origin.
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The Science Museum Group says early versions date back to the 1600s, while noting that the date and maker of its Shuttleworth example are unclear. It separately records a W.F. Stanley elliptic trammel dated 1876. Those collection records document examples; they do not identify the original inventor. Science Museum Group: Shuttleworth elliptic trammels Science Museum Group: W.F. Stanley elliptic trammel, 1876
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