[Jeff Higgins]

I grew up using a pair of trammel points as an apprentice tool maker at a large commercial aircraft manufacturer. We most commonly used them as a big set of dividers when laying out locations of tooling components on what is known as a "surface table". This table is ground flat within a few tenths (.0001") and leveled via jack screws while being shot with a surveyor's transit. We would paint the top of it with Dykem Blue so the scribe lines imparted by the trammel points would show up better.

Not apparent in the photos is that the points are offset. This allows one to twist the shaft in the clamp to make fine adjustments. We would typically use a steel scale to set the distance between the points, since the sharp point will catch the hash marks on the scale. We would clamp the trammel points to a piece of wood, or a piece of aluminum square tubing of appropriate length.

Surprisingly accurate work can be done with these. We were held to a tolerance of +/- .010" when doing this kind of layout work. This experience served me well as I later transitioned to an engineering career, and, at first (pre CAD days), a drafting board.