SOME COMMON MACHINES 527 



In the oscillating-hook or oscillating-shuttle machine, the 

 hook or shuttle makes one-half of a rotation, i.e., turns one- 

 half way around on its axis, and then reverses and returns to 

 its former position, for each stitch. 



In the vibrating-shuttle machine the shuttle may move in a 

 straight line or in the arc of a circle. In either case, the shuttle 

 makes one complete vibration, i.e., a motion forward and back, 

 for each stitch. 



Exercise 101. A Study of the Sewing Machine 



(This exercise may be studied at home if no machine is available 

 at school.) 



1. Note the name of the machine. 



2. Note just how the motion of the treadle is transferred to the 

 drive wheel by means of the PITMAN. One complete vibration of 

 the treadle produces how many revolutions' of the drive wheel? 



FIG. 328. Head of a vibrating-shuttle machine. 



3. Measure the diameter of the drive wheel. What, then, is its 

 circumference? Measure the diameter of the pulley on the head of 

 the machine over which the belt passes. What is its circumference? 



4. Provided there is no slipping of the belt, how many revolutions 

 of the pulley will be produced by one revolution of the drive wheel? 



5. Turn the pulley carefully and see how many stitches are taken 

 by the needle for each revolution of the pulley. How many stitches 

 are taken, then, to each complete vibration of the treadle? Move 

 the treadle through one complete vibration and count the number of 

 stitches taken to check your calculation. 



