426 APPLIED SCIENCE 



bed is the distance the tail-stock will move backward. If 

 accuracy is desired, this measurement should be the distance 

 between the two centers when the tail-stock is pushed back- 

 ward as far as it will go. The length of the piece the lathe 

 will turn is limited by the % distance between its centers. 



490. Simple and Compound Lathes. A simple or single- 

 geared lathe has a straight train of gearing from its spindle 

 to its feed screw, with intermediate gears which serve as 

 idlers to take up the distance between the driver and driver 

 gears or spindle and screw gears. Index plates, giving the 

 change of gear used for different threads, are usually found on 

 lathes, but when threads are called for that are not indexed 

 or when those ending in fractions are to be cut, the machinist 

 must resort to his own figures. 



The term compound in lathe practice means that in the 

 train of gearing from the spindle to the lead screws of the 

 lathe, there is a stud or spindle with two different sized gears. 

 These gears are so connected as to change the link of revolu- 

 tion between the spindle and the lead screw to a different 

 number of revolutions from that which would take place if 

 the straight line of gears were used. 



491. Lathe Tools. The ordinary lathe tool is a short 

 bar or rectangular cross-section of tool steel with a cutting 

 edge at one end. It is produced by forging and grinding. 

 It must be hardened and tempered to cut the metals upon 

 which it is to operate. The lathe chuck is a device for hold- 

 ing the work firmly and adjusting it accurately. 



492. Vise. The machinist's vise is one of the simplest 

 as well as one of the most important parts of the machine- 



