212 FARM MACHINERY 



through. The endless apron was the first device used 

 and is now found in only a few machines, and there only 

 in short lengths. 



The oscillating rack is made in sections and attached 

 to a crank shaft directly. The sections are made to bal- 

 ance each other and offer a great advantage in this re- 

 spect. An oscillator is a very good device for separating 

 the grain, but perhaps somewhat difficult to keep in re- 

 pair. 



The vibrating rack may be made in one or more sec- 

 tions. When made in one section there is usually an 

 attempt to balance its motion with that of the grain pan. 

 The rack is provided with notched fingers, called "fish- 

 backs." These are given a backward and upward thrust 

 by a pitman attached to a crank, causing the rack to 

 swing on its supports. This motion causes the straw to 

 move backward and at the same time be thoroughly agi- 

 tated. Machines are constructed with two racks, the 

 upper to carry off the coarse straw and a lower to sepa- 

 rate the finer. The double rack permits of their motion 

 being balanced the same as the rack built in two 

 sections. 



291. The grain conveyor or grain pan extends from 

 under the cylinder back almost the full length of the 

 machine. Its function is to convey the grain to the 

 cleaning mechanism. It should be of light, yet strong, 

 construction. It must not sag, or grain will be pocketed 

 in such a manner that its motion will not cause it to 

 pass on. 



292. Chaffer. At the end of the grain conveyor and 

 really forming a part of it is the chaffer, which is a sieve 

 with larre openings permitting all but the coarse straw 

 to pass through. A part of the blast from the fan passes 

 through the chaffer, and a large portion is carried off in 



