38 SCIENCE OF THRESHING. 



It will be seen that if the straw rack had a slight 

 motion, it would not handle or scarcely move the 

 straw at all, while if the conveyor and chaffer sieves 

 had as much motion as the straw rack, they would 

 throw the grain so fiercely as to prevent a good 

 portion of it from passing through. This is because 

 of the difference in the elasticity or springiness of the 

 materials to be moved. It is thus quite essential that 

 the motion should be adapted to the class of work to 

 be done. In end shake sieves, that is, where the 

 stroke is endwise of the machine, this motion should 

 be upwards and backwards with quite an uplift, and 

 should be just strong or rapid enough to cause the 

 grain to be carried along as quietly as possible. 



In side shake sieves, that is, where the motion is 

 sidewise to the machine, the motion should be suffi- 

 ciently strong and long to cause the sieve to move 

 continually under the grain and chaff, thereby aiding 

 the blast in carrying the chaff along toward the rear. 



The blast may be at a greater angle from the 

 perpendicular in side shake sieves than in end shake 

 sieves as it is the only means of carrying the chaff and 

 refuse along to the rear. 



In the end shake sieve, the upward and backward 

 motion assists in moving the mass. 



Side shake sieves may be given an upward 

 rocking at each side, as the stroke is finished. 

 This is accomplished by using comparatively short 

 hangers and adjusting them at an angle (sidewise to 

 the machine). As the sieve is moved sideways, one 

 side will continue to rise, and the other to lower 



