208 FARM MACHINERY 



shrinking wrought-iron bands over the bars. A solid 

 cylinder may be used instead of the bars. The bars in some 

 makes are made of two pieces, and hence are called 

 double-barred cylinders. The teeth are held in place by 

 nuts or wedges, and are often provided with lock washers. 

 Wooden bars may be placed under the nuts and act as a 

 cushion, preventing the teeth from loosening as readily 

 as otherwise. The cylinder has usually 9, 12, or 20 bars, 

 the latter being spoken of as a big cylinder. 



The cylinder travels with a peripheral speed of about 

 6,000 feet a minute. The usual speed for the 12-bar 

 cylinder is 1,100 revolutions per minute, and of the 2O-bar 

 cylinder is 800 revolutions per minute. A large amount of 

 power is stored in the cylinder when in motion and 

 enables the machine to maintain its speed when an undue 

 amount of straw enters the cylinder at a time. 



The kernels of grain should be removed from the heads 

 and retaining hulls in passing through the cylinder. The 

 other devices in the machine do not have a threshing 

 effect. In threshing damp, tough grain, a higher speed 

 must be maintained than when threshing dry grain. It 

 is attempted, however, to run the cylinder at about uni- 

 form speed in nearly all cases. 



As the cylinder is heavy and travels at a high speed, 

 it must be properly balanced, or it will not run smoothly. 

 In the factory the cylinder is made up and then balanced 

 by running at a high speed on loose boxes. The heavy 

 side is located by holding a piece of chalk against the 

 cylinder while in motion. When the cylinder teeth be- 

 come worn they must be replaced with new teeth, which 

 are heavier, so that there is a tendency to put the cylinder 

 out of balance. After putting in new teeth the cylinder 

 may be balanced by removing from the machine and 

 mounting it on two level straight edges placed on saw 



