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EXAMPLE QUESTIONS AND ANSWERS (4)

V. Ryan 2001

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Below is a question regarding 'compound gears'. Gears C and B represent a compound gear as they appear 'fixed' together. When drawn with a compass they have the same centre. Two gears 'fixed' together in this way rotate together and at the same RPM. When answering a question like this split it into two parts. Treat gears A and B as one question AND C and D as the second part.

     

 

This is an example of a compound gear train. Gear A rotates in a clockwise direction at 30 revs/min. What is the output in revs/min at D and what is the direction of rotation ?

     

GEAR A

GEAR B

GEAR C

GEAR D

120 T

40 T

80 T

20 T

First find revs/min at B;

B is smaller therefore it rotates faster and revs/min increase.

C is fixed to B and therefore, rotates at the same speed.

90 REVS/MIN at C

Next find revs/min at D

D is smaller than C, therefore rotates faster (increased revs/min).

A revolves in a clockwise direction, B is therefore anti-clockwise, C is fixed to B and is also anti-clockwise, which means D revolves in a clockwise direction.

 
 
 
 
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