FARM MACHINERY 



279 



The Concave. The concave is made up of heavy bars 

 into which teeth similar to cylinder teeth are fastened. It is 

 located below the cylinder, and receives its name from its 

 shape. The number of rows of teeth may vary according 

 to the kind and condition of threshing, and may be varied 

 by inserting removing bars. The concave may be adjusted 

 by raising or lowering, the threshing effect being greater 

 when the teeth are high and entered well into the teeth of 

 the cylinder. 



The Grate. The grate consists of a number of parallel 

 bars with open spaces between, placed directly beyond the 



Fig. 177. A section of a modern threshing machine. 



concave teeth. A large part of the grain and chaff is allowed 

 to pass through this grate before reaching the straw rack 

 beyond. 



The beater is a webbed wheel beyond the cylinder, which 

 beats the straw into a stream as it comes from the cylinder 

 and enables it to be passed quickly over the straw rack. 



The Straw Rack. The straw rack is a vibrating rack 

 which allows the stream of straw to pass over it but which 

 sifts out the grain. There are many types of straw racks 

 in use, and these vary in their construction and shaking 

 motion. 



