Machine Design
If T is the actual number of teeth on a helical gear and φ is the helix angle for the teeth, then formative number of teeth is written as

T/sec³φ
T sec³φ
T cosecφ
T sec²φ

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Machine Design
Elastic nut is a locking device in which

One small nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming
Through slots are made at top and a cotter pin is passed through these and a hole in the bolt, and cotter pin splitted and bent in reverse direction at other end
Hard fibre or nylon cotter is recessed in the nut and becomes threaded as the nut is stewed on the bolt causing a tight grip
A slot is cut partly in middle of nut and then slot reduced by tightening a screw

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Machine Design
In oilness bearings

The oil film pressure is generated only by the rotation of the journal
The oil film is maintained by supplying oil under pressure
Grease required to be applied after some intervals
Do not require external supply of lubricant

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