218 



AGRICULTURAL ENGINEERING 



Fig. 127. An alfalfa harrow. 



disk harrow. This new implement is certain to become 



very popular for cultivating alfalfa fields. 



Scrapers. A disk harrow should be provided with 



scrapers or cleaners which 

 will keep the disks clean 

 under all conditions. The 

 scraper with a rather nar- 

 row chisel blade which 

 can be moved from the 

 center to the outside of 

 the disk is very satisfac- 

 tory and is used upon 



a large number of modern disk harrows. 



Bearings. The part that receives the most wear, except 



the cutting edges of the disks themselves, is the bearings. 



Both chilled iron and wooden boxes are used. The wood 



seems to be the more satisfactory, not only on account of 



durability, but also on account of the ease of replacement. 



Maple boiled in oil is generally used for the bearings, yet any 



hard wood might answer. 



Ball-and-socket joints between the disks are not generally 



satisfactory. If the bearings 



do not care for the entire 



thrust of the gangs, bumper 



plates seem to be the most sat- 

 isfactory devices. These are 



large oval washers on the ends 



of the gang bolts which run 



through the center of the disks. 



Tongue Truck. The modern disk harrow has a tongue 



truck. This device relieves the horses of the most tiresome 



part of the work when the harrow is used on loose and rough 



ground. With a tongue truck, side lashing is prevented. 



8. A good form of bearing 

 for disk harrows. 



