THE SCREW 63 



EXERCISE 60 

 THE SCREW 



Apparatus and Materials. Steel screw, metric rule, board of soft 

 wood, hammer, screw driver, carpenter's brace, screw-driver bit. 

 For examination: -copying press, jackscrew, carpenter's wood screws. 



a. Examine an ordinary steel screw, measure accurately 

 the threaded part, and count the number of threads. What is 

 the distance between two successive threads? 



6. Force a screw into a piece of soft wood. To do this, first 

 give the head of the screw a tap or two with a hammer, so as 

 to " start" the screw. Then use a screw driver, giving it a 

 few turns. Can you turn the screw with the fingers alone? 

 Why? 



c. Find out how far it is around the screw-driver handle 

 (circumference) at its thickest part. If the screw driver has 

 flat sides, get its greatest thickness (diameter) and multiply 

 this by 3y. Compare the circumference of the handle with 

 the distance between threads. How far must the hand be 

 turned in order to make the screw advance the distance between 

 two successive threads? If you exert a force of 1 kg. on the 

 circumference of the screw driver, how much do you exert on 

 the threads? 



d. Go to a hardware store, and ask to see the different vari- 

 eties of screws. Ask for what each kind is used. How are the 

 sizes of screws stated? Ask to see a copying press, a jackscrew, 

 and carpenters' wood screws, and have their uses explained to 

 you. 



e. Examine a carpenter's brace, and put into it the screw- 

 driver bit. Use this to drive the screw farther into the wood. 

 Can you drive the screw more, or less, easily than with the 

 screw driver? Why? 



Find out how large a circle your hand goes through in turning 



