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Aviation History
1952
1952 - 0558.PDF
PRECISION FACTORS CONTRIBUTING TO 29 FEBRUARY 1952 ENGINE EFFICIENCY Inspecting Helic WlflGdS A feature contributing to the quiet running and long life of "Bristol" engines is the precision manufacture of gearwheels. It is normal practice at "Bristol" for spur gear teeth to be finished by grinding, and to ensure the requisite degree of accuracy a very careful inspection is carried out. One of the instruments in current use at "Bristol" is the "Maag" testing machine, which measures and records any deviations from the ideal involute tooth profile with a magnification of 500 times. The above illustration shows a gearwheel mounted on a mandrel for testing. The mandrel is supported on a disc of diameter equal to that of the base circle of the gearwheel. This disc is rolled along a straight track, and a follower is placed in contact with the tooth being inspected. _l 1 i 1- ~ -T-JM-.E m iiii ^rfff '- ' •••[ -!— i^g ~j [~i"fe __ •i.ff jag TfTT: Bffifljt The principle is shown diagrammatically above where it can be seen that the follower will only deflect if the tooth is not a pure involute. A pen coupled to the follower records on a rotating drum the result of traversing the tooth flank, any movement of the follower being greatly magnified. A pure involute would produce a straight line on the chart. Sample traverses for three tooth flanks are shown on the left. Intentional deviation, such as tip relief, can also be measured from the chart. This machine is one of many precision tools in constant use in the "Bristol" workshops. Typical chart produced by the testing machine. Sleeve-valve and turbine engines for reliability THE BRISTOL AEROPLANE COMPANY LIMITED onomy UUV 998£ ENGLAND
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