142 SCIENCE OF SUCCESSFUL THRESHING. 



prevent the risers from sagging in the middle. (See cut, 

 page 120). 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 straw-rack ordinarily does good 

 work without the fish-backs, but in cases where the separa- 

 tion is very difficult, they will aid materially. 



A Special Strazv-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 

 an Oregon rack of the regular one. 



Pounding. The crank-boxes and pitmans should be kept 

 adjusted so that the machine does not make a knocking 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 often breaks the vi- 

 brating arms. The rear vibrating 1 arms may be prevented 

 from dropping too low in three ways : first, 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. 



