l68 SCIENCE OF SUCCESSFUL THRESHING 



which prevent the risers from sagging in the middle. (See 

 Fig. 43). Fish-backs are nailed to the straw-rack risers, 

 two on the second riser (from the front), three on the 

 third and four on the fourth. The fish-backs aid mater- 

 ially in separation. 



A Special Straw-Rack called the "Oregon" straw-rack 

 is made for use where the straw is badly cut up or so short 

 owing to the grain being headed that most of it passes 

 through the regular rack. Parts can be furnished for 

 making the regular rack into one of the Oregon style. 



Pounding. The crank-boxes and pitmans should be 

 kept adjusted so that the machine does not make a knock- 

 ing or pounding noise. The maple boxes on the straw- 

 rack and conveyor are inexpensive and should be replaced 

 when worn out. The pitmans shorten as they wear, and 

 this, with the wear of the crank boxes, sometimes allows 

 the rear vibrating arms to drop nearly to their dead-centers. 

 This causes the machine to run hard, pound badly, and is 

 liable to break the vibrating arms. The rear vibrating 

 arms may be prevented from dropping too low in three 

 ways: first, by moving the, crank-shaft ; if the frame be of 

 wood, the crank boxes may be moved forward by putting 

 leather between them and the post ; second, by lengthening 

 pitmans by putting leather over worn surface at ends or 

 by getting new and longer pitmans ; and third, by moving 

 the rock-shaft boxes to the rear. This last method is the 

 most difficult and should it be attempted, care must be taken 

 to move all the boxes exactly the same distance. 



