THE CLEANING APPARATUS 173 



Twenty-penny wire nails may be used as pins in adjusting 

 sieves. 



Screens. A screen removes particles smaller than the 

 grain or seed being threshed, such as weed seeds, sand, or 

 other foreign matter which is generally valueless. Some- 

 times, however, a useful seed,, such as timothy is screened 

 out of one of the large grains, as wheat. In general, for 

 weed seeds that are approximately round, the round hole 

 are better than the oblong hole screens. However, the lat- 

 ter are the only ones that will take out "cheat" which is 

 often found in wheat. The screen lies in the bottom of the 

 shoe and is held in place by hooks with thumb nuts which 

 engage castings fastened on the frame of the screen. When 

 a screen is used the removable strip in the bottom of the 

 shoe must be taken out to allow the screenings to fall to the 

 ground. All screens are liable to become clogged and in 

 this condition obstruct the passage of the grain and wind. 

 They should therefore be kept clean and only used when 

 necessary. The list of screens is given on page 172 and 

 they are illustrated on page 173. 



The Tailings Elevator returns to the cylinder for a 

 second threshing the unthreshed heads and all trash 

 dropped through the straw-rack which is too coarse to fall 

 through the sieves and too heavy to be blown out by the 

 blast. It consists of an elevator (with cups or flights 

 carried on sprocket chain), into which the tailings are de- 

 livered by an auger (called the tailings auger) and a spout 



