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PULLEY EXAMINATION - QUESTION

V. Ryan © 2006-2017

 

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Pulley systems are used widely in industry and on production lines. The power hacksaw shown below moves backwards and forwards continuously, cutting metal. A basic drawing of this machine is shown below.

The diagram has been divided into two sides - A and B

1. On side ‘A’ add a pulley system that connects shaft 1 and 2 so that two different speeds can be selected. USE NOTES AND SKETCHES

2. On side ‘B’ show how a single pulley is held securely on to the shaft. USE NOTES AND SKETCHES

   
POSSIBLE ANSWER
 
Two pulley wheels are added to shaft 2. They have different diameters.

Changing to the large pulley slows down movement of the hacksaw.

Changing to the small pulley speeds up movement
A cotter pin can be used. It is tapped through a hole that runs through the pulley and the shaft, holding it firmly together.  
     
2b. Why are different speeds needed for the power hacksaw needed?  
   
   
   
POSSIBLE ANSWER  
     
2b. Why are different speeds needed for the power hacksaw needed?  

Each type of metal has a particular speed at which it can be cut efficiently. Choosing the wrong speed may damage the blade and it may take longer to cut through the metal.

 
     
     
3. To make the power hacksaw safe to use to ‘push to make’ (PTM) switches have been added. The incomplete circuit below shows one of the switches in position. Complete the circuit be adding the second switch.  
     
 

POSSIBLE ANSWER

 
   
   
3b. What is the colour of the ON button of any machine?
 
3c. What is the colour of the OFF button of any machine?
 
   
POSSIBLE ANSWER
   
3b. What is the colour of the ON button of any machine?
GREEN IS NORMALLY THE 'ON' BUTTON
 
3c. What is the colour of the OFF button of any machine?
RED IS NORMALLY THE 'OFF' BUTTON
 
4. Why should the switches be placed at least 500mm apart?
 
 
   

POSSIBLE ANSWER

   
4. Why should the switches be placed at least 500mm apart?
 

Placing the buttons 500mm apart means that both hands of the operator must be used to turn the machine on. This means that the operators hands cannot be near the saw blade.

   

5. The drawing of a new style of power hacksaw needs two types of switches - a foot switch and a normal ON/OFF switch. Draw each switch in its best position on the diagram and explain your reasoning with notes.

 
   
POSSIBLE ANSWER
   
   
POSITION OF FOOT SWITCH - EXPLANATION:
 
 
   
POSITION OF NORMAL SWITCH - EXPLANATION:
 
 
   
POSSIBLE ANSWERS
   
POSITION OF FOOT SWITCH - EXPLANATION:

The operator can stand at the front and watch the machine working. He/she can turn it off using the foot switch without getting close to the moving blade.

   
POSITION OF NORMAL SWITCH - EXPLANATION:

The operator can stand at the side of the machine and switch it on, then move to a more suitable position to watch it cut.

     
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