Beam compass

A draftsman's beam compass consists of a set of points and holders, mounted on a plated brass, aluminum, or German 'silver'[2][3] rod.

The locked tip holder consists of a needle, for the centre of the radius, and the other holds either a lead clutch, or an inking nib.

The beam compass is used to scribe a circle, either by drawing with lead, penning by ink, or scratching with a sharpened point.

Some trammel sets include a support roller for attachment at mid span of the beam or rod, to take out the sag.

Each point is rotated 180° along a straight line or large circle, and this process is repeated until the desired measurement or division is reached.

This cutter is used primarily to score a circular pattern in the drywall to fit over recessed lighting in the ceiling.

The tool consists of a square shank with a sliding pivot that is locked into the desired location with a turn knob.

Keuffel & Esser Arrow Beam Compass Set for Drafting.
sharp point used to score a fine line in the birch plywood connected to each other by a piece of 3/4" × 3/8" mahogany
Circle cutter used to score drywall.