What is "beam compass"

Compass \Com"pass\ (k[u^]m"pas), n. [F. compas, fr. LL. compassus circle, prop., a stepping together; com- + passus pace, step. See Pace, Pass.]

1. A passing round; circuit; circuitous course.

   They fetched a compass of seven day's journey.
   --2 Kings iii. 9.

   This day I breathed first; time is come round, And where I did begin, there shall I end; My life is run his compass.
   --Shak.

2. An inclosing limit; boundary; circumference; as, within the compass of an encircling wall.

3. An inclosed space; an area; extent.

   Their wisdom . . . lies in a very narrow compass.
   --Addison.

4. Extent; reach; sweep; capacity; sphere; as, the compass of his eye; the compass of imagination.

   The compass of his argument.
   --Wordsworth.

5. Moderate bounds, limits of truth; moderation; due limits; -- used with within.

   In two hundred years before (I speak within compass), no such commission had been executed.
   --Sir J. Davies.

6. (Mus.) The range of notes, or tones, within the capacity of a voice or instrument.

   You would sound me from my lowest note to the top of my compass.
   --Shak.

7. An instrument for determining directions upon the earth's surface by means of a magnetized bar or needle turning freely upon a pivot and pointing in a northerly and southerly direction.

   He that first discovered the use of the compass did more for the supplying and increase of useful commodities than those who built workhouses.
   --Locke.

8. A pair of compasses. [R.] See Compasses.

   To fix one foot of their compass wherever they please.
   --Swift.

9. A circle; a continent. [Obs.]

   The tryne compas [the threefold world containing earth, sea, and heaven.
   --Skeat.]
   --Chaucer.

   Azimuth compass. See under Azimuth.

   Beam compass. See under Beam.

   Compass card, the circular card attached to the needles of a mariner's compass, on which are marked the thirty-two points or rhumbs.

   Compass dial, a small pocket compass fitted with a sundial to tell the hour of the day.

   Compass plane (Carp.), a plane, convex in the direction of its length on the under side, for smoothing the concave faces of curved woodwork.

   Compass plant, Compass flower (Bot.), a plant of the American prairies ( Silphium laciniatum), not unlike a small sunflower; rosinweed. Its lower and root leaves are vertical, and on the prairies are disposed to present their edges north and south.

   Its leaves are turned to the north as true as the magnet: This is the compass flower.
   --Longefellow.

   Compass saw, a saw with a narrow blade, which will cut in a curve; -- called also fret saw and keyhole saw.

   Compass timber (Shipbuilding), curved or crooked timber.

   Compass window (Arch.), a circular bay window or oriel window.

   Mariner's compass, a kind of compass used in navigation. It has two or more magnetic needles permanently attached to a card, which moves freely upon a pivot, and is read with reference to a mark on the box representing the ship's head. The card is divided into thirty-two points, called also rhumbs, and the glass-covered box or bowl containing it is suspended in gimbals within the binnacle, in order to preserve its horizontal position.

   Surveyor's compass, an instrument used in surveying for measuring horizontal angles. See Circumferentor.

   Variation compass, a compass of delicate construction, used in observations on the variations of the needle.

   To fetch a compass, to make a circuit.

Beam \Beam\ (b[=e]m), n. [AS. be['a]m beam, post, tree, ray of light; akin to OFries. b[=a]m tree, OS. b[=o]m, D. boom, OHG. boum, poum, G. baum, Icel. ba[eth]mr, Goth. bagms and Gr. fy^ma a growth, fy^nai to become, to be. Cf. L. radius staff, rod, spoke of a wheel, beam or ray, and G. strahl arrow, spoke of a wheel, ray or beam, flash of lightning. [root]97. See Be; cf. Boom a spar.]

1. Any large piece of timber or iron long in proportion to its thickness, and prepared for use.

2. One of the principal horizontal timbers of a building or ship.

   The beams of a vessel are strong pieces of timber stretching across from side to side to support the decks.
   --Totten.

3. The width of a vessel; as, one vessel is said to have more beam than another.

4. The bar of a balance, from the ends of which the scales are suspended.

   The doubtful beam long nods from side to side.
   --Pope.

5. The principal stem or horn of a stag or other deer, which bears the antlers, or branches.

6. The pole of a carriage. [Poetic]
   --Dryden.

7. A cylinder of wood, making part of a loom, on which weavers wind the warp before weaving; also, the cylinder on which the cloth is rolled, as it is woven; one being called the fore beam, the other the back beam.

8. The straight part or shank of an anchor.

9. The main part of a plow, to which the handles and colter are secured, and to the end of which are attached the oxen or horses that draw it.

10. (Steam Engine) A heavy iron lever having an oscillating motion on a central axis, one end of which is connected with the piston rod from which it receives motion, and the other with the crank of the wheel shaft; -- called also working beam or walking beam.

11. A ray or collection of parallel rays emitted from the sun or other luminous body; as, a beam of light, or of heat.

    How far that little candle throws his beams!
    --Shak.

12. (Fig.): A ray; a gleam; as, a beam of comfort.

    Mercy with her genial beam.
    --Keble.

13. One of the long feathers in the wing of a hawk; -- called also beam feather.

    Abaft the beam (Naut.), in an arc of the horizon between a line that crosses the ship at right angles, or in the direction of her beams, and that point of the compass toward which her stern is directed.

    Beam center (Mach.), the fulcrum or pin on which the working beam of an engine vibrates.

    Beam compass, an instrument consisting of a rod or beam, having sliding sockets that carry steel or pencil points; -- used for drawing or describing large circles.

    Beam engine, a steam engine having a working beam to transmit power, in distinction from one which has its piston rod attached directly to the crank of the wheel shaft.

    Before the beam (Naut.), in an arc of the horizon included between a line that crosses the ship at right angles and that point of the compass toward which the ship steers.

    On the beam, in a line with the beams, or at right angles with the keel.

    On the weather beam, on the side of a ship which faces the wind.

    To be on her beam ends, to incline, as a vessel, so much on one side that her beams approach a vertical position.

n. a device for creating circle curves, which has a central pivot pin, and an outer curb scribing point, connected by a horizontal beam

A beam compass is a compass with a beam and sliding sockets or cursors for drawing and dividing circles larger than those made by a regular pair of compasses. The instrument can be as a whole, or made on the spot with individual sockets (called trammel points) and any suitable beam.