Beam compass

Claim 2

A beam compass comprising: a. a trammel head including 1. a hollow slide body having an outer face and three, approximately equiangularly offset inner faces bounding a passage extending in a predetermined direction through said slide body, 2. a guide rail projecting from each of said inner faces into said passage, each guide rail being elongated in said direction,

Claim 3

an arm mounted on said slide body and projecting from said outer face perpendicularly to said direction, said arm having a free end remote from said slide, and 4. attaching means for attaching a compass point to said free end; b. an elongated scale of triangular cross section having three longitudinal faces formed with respective longitudinal grooves, 1. said scale being received in said passage, 2. said rails respectively engaging said scale in said grooves, 3. each of said longitudinal faces being separated from a respective one of said inner faces by a clearance; and c. clamping means on said trammel head spaced from said rails for securing said slide body to said scale.

Claim 4

an arm mounted on said slide body and projecting from said outer face perpendicularly to said direction, said arm having a free end remote from said slide, and 4. attaching means for attaching a compass point to said free end; b. an elongated scale of triangular cross section having three longitudinal faces formed with respective longitudinal grooves, 1. said scale being received in said passage, 2. said rails respectively engaging said scale in said grooves, 3. each of said longitudinal faces being separated from a respective one of said inner faces by a clearance; and c. clamping means on said trammel head spaced from said rails for securing said slide body to said scale.

Claim 5

A beam compass as set forth in claim 1, wherein said slide body is formed with a slot extending therethrough between said passage and said outer face, said clamping means bridging said slot for varying the width of said slot and for thereby varying the cross section of said passage.

Claim 6

A beam compass as set forth in claim 1, wherein said passage has an axis extending therethrough in said direction, said guide rails being distributed approximately equiangularly about said axis.

Claim 7

A beam compass as set forth in claim 3, wherein each of said guide rails has a tubular portion integral with said slide body, and a reinforcing portion conformingly received in said tubular portion, said reinforcing portion being elongated in said direction.

Claim 8

A beam compass as set forth in claim 4, wherein said slide body and said tubular portion jointly constitute a unitary body of synthetic resin composition, and said reinforcing portion consists of metallic material.

Claim 9

A beam compass as set forth in claim 3, wherein said inner faces are formed with respective grooves elongated in said direction and receiving said guide rails, said guide rails consisting essentially of metallic material.

Claim 10

A beam compass as set forth in claim 1, a ring mounted on said free end for rotation about an axis perpendicular to said direction.

Claim 11

A beam compass as set forth in claim 1, further comprising a handle member mounted on said slide body and projecting from said outer wall in alignment with and away from said arm.

Claim 12

A beam compass as set forth in claim 1, further comprising another arm mounted on said slide body and projecting from said outer wall in alignment with and away from said first-mentioned arm, said other arm having a free end remote from said slide body, and attaching means for attaching a compass point to the free end of said other arm.

Claim 13

A head as set forth in claim 1, wherein each of said guide rails is permanently fixed to the associated inner face.

Claim 14

A beam compass as set forth in claim 1, wherein one of said longitudinal faces carries calibration markings.