218 AGRICULTURAL ENGINEERING 



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- 



Fig. 127. An alfalfa harrow. 



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 aje 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 FigTm. A^ood form of bearing 



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. 



