Simplifying Gear-tooth Measurement
Page 31
If you've noticed an error in this article please click here to report it so we can fix it.
Bench-type Version of the David Brown Tangent Micrometer for Use in Gear-making
I N our issue dated September 1, we made reference to a hand-type of tangent micrometer for use in making gear-tooth measurements. David Brown and Sons (Huddersfield), Ltd.. Huddersfield, the concern responsible for this'instrument, has now produced a logical development in the form of a bench-type instrument on more pretentious lines.
The basic principle underlying the design of the David Brown micrometer is that the length of a tangent to the base circle of an involute gear between the opposite flanks of any two teeth cut by that tangent is constant, no matter at what angle the tangent may be drawn.
In practice, the actual measurement is taken over a number of teeth and compared with a calculated dimension to which the micrometer has previously been set.
As compared with a standard type of gear-tooth calliper, certain distinct advantages are claimed for the David Brown instrument. Amongst them may be mentioned that it is necessary to make only one measurement, this being entirely independent of the outside diameter of the gear; as the reading is given on a dial indicator greater accuracy is possible; once set it will, without re-adjustment, give a direct indication of the amount by which the measured thickness differs from the correct value.
The instrument is designed for bench mounting and the main framework measures, approximately, 15 ins. by 19 ins. by 3 ins, A vertical pillar carrying the gauging head, is carried on this base, and there are two parallel bars, arranged horizontally, upon which to rest the gear being tested. These bars are adjustable, in a lateral sense, to accommodate gears of various dia * meters.
The framework of the gauging head is bored to suit the vertical pillar, and is provided with two rigid arms carrying the gauging anvils and clock-indicating mechanism. The left-hand anvil is adjustable, along a hardened and ground bar, to suit the different gears to be gauged, whilst the right-hand anvil is securely fixed to a floating, sensitive carriage—mounted on ball bearings—which is normally held against a stop. , When the gear teeth being gauged are inserted between the anvils, this floating carriage moves outwards to operate the dial indicator by means of a hardened and .ground button.
It may be of interest to mention that David Brown and Sons (Huddersfield), Ltd., has acquired control of the share capital of Muir Machine Tools, Ltd., Britannia Works, Manchester, a century-old concern associated with gearmaking machinery.