sine bar

sine bar
Name	Sine bar
Classification	Precision measuring tool
Used for	Setting angles, inspection, calibration
Invented	19th century (approx.)
Manufacturers	Starrett, Mitutoyo, Brown & Sharpe, Moore

sine bar

A precision measuring tool used for setting and measuring angles in metalworking and inspection, the device employs trigonometric principles to convert linear height into angular displacement. It is widely used in machine shops, toolrooms, metrology laboratories, and by instrument makers to achieve accurate angular setups for milling, grinding, and inspection tasks. Typical contexts include work associated with Henry Maudslay-era machine tools, standards labs such as the National Institute of Standards and Technology, and firms like Brown & Sharpe and Mitutoyo.

Description

A sine bar is a hardened, precision-ground steel bar with two cylindrical rollers or bosses mounted at its ends; the centers of the cylinders define a baseline used with precision gauges. In practice, the tool is paired with gauge blocks from makers like Carl Zeiss AG or standards produced by the International Organization for Standardization to establish known heights. Operators commonly employ surface plates from manufacturers such as Granite (material) suppliers or metrology tables in facilities exemplified by Sandia National Laboratories and Los Alamos National Laboratory.

Construction and design

Typical construction uses hardened tool steel or stabilized alloy with ground flat surfaces and accurately lapped cylindrical rollers affixed at a precise center-to-center distance, often 100 mm, 200 mm, or an inch-based distance reflecting practices of companies like Brown & Sharpe and Starrett. The cylindrical rollers are made to close tolerances to ensure concentricity and parallelism; companies such as Mitutoyo and Moore Tool Company produce calibration certificates that reference national metrology institutes like the National Physical Laboratory (United Kingdom). Designs may include lightening holes, tapped mounting points for fixtures, and datum faces for clamping on machine vises used in facilities similar to General Electric toolrooms.

Principle of operation

Operation relies on the trigonometric sine function: angle = arcsin(opposite/hypotenuse), where the gauge-block stack provides the "opposite" height and the bar center-to-center distance provides the "hypotenuse." This method mirrors principles applied in classical works on precision measurement from figures such as Joseph Whitworth and institutions like the Royal Society. Users compute angles for setups in concert with angular measuring instruments like bevel protractors from Starrett or optical comparators produced by Federal Products Corporation.

Use and applications

In machining, inspection, and toolmaking, the device is used to set compound angles for milling, grinding, layout work, and jig and fixture inspection; such activities are typical in historical contexts affiliated with Vickers Limited and modern aerospace firms like Boeing and Lockheed Martin. Metrology labs in universities such as Massachusetts Institute of Technology and Technical University of Munich use sine bars for research and calibration. It is also used in conjunction with surface gauges from Brown & Sharpe, height gauges from Mitutoyo, and coordinate measuring machines in quality control environments like those at Siemens plants.

Accuracy and calibration

Accuracy depends on the precision of the center-to-center distance, the flatness of contact surfaces, the straightness and concentricity of the rollers, and the correctness and traceability of gauge blocks referenced to standards from organizations such as the International Bureau of Weights and Measures. Calibration procedures often involve comparison to angle blocks, rotary tables manufactured by firms like Heidenhain, and interferometric standards used in national labs including NIST. Environmental factors such as temperature control in metrology labs at institutions like CERN or Fraunhofer Society affect measurement uncertainty, which is evaluated following standards developed by bodies such as the International Electrotechnical Commission.

Variants and related tools

Variants include sine plates, adjustable sine tables, and precision angle blocks; related tools encompass bevel protractors by Starrett, optical flats from Carl Zeiss AG, autocollimators produced by Renishaw, and rotary tables by Heidenhain. Specialized fixtures used in gear inspection at firms like AGMA members and precision grinding shops often integrate sine devices with surface plates and coordinate measuring machines by companies such as Zeiss and Hexagon AB.

Category:Precision instruments