PLOWS FOR MECHANICAL POWER 181 



Lengthening the chain between the engine and the rear of the 

 gant is one common method of changing the angle of the disks. 



With twenty-four-inch disks, furrows from four to eight 

 inches deep and eight to twelve inches wide may be cut. One 

 prominent designer recommends plowing furrows not less than 

 five or six inches deep and not over eight inches, preferably 

 seven, wide. The deeper the furrow the less prominent the 

 "hogbacks" left on the surface, and at a depth of six inches 

 a disk cutting not over seven inches wide will break out the 

 triangular space between it and the next disk and leave the 

 bottom of the furrow practically level. As a rule, however, 

 the average user cuts nine or ten inches with each disk, and 

 many not over four inches deep in the centre of the furrow. 

 In consequence, while more ground is covered, a seed bed of 

 uneven depth is formed. 



Different makes of disk plows vary considerably in strength 

 and durability. The frame must be very well braced, and the 

 castings heavy. Even with the best construction, simplicity 

 brings the cost low as compared with the best moldboard gangs. 

 If the disks are properly set and held in place, breakage is much 

 less frequent than where some play is allowed, and the disks 

 are to some extent self-sharpening. A twenty-four-inch 

 disk has nearly four times the cutting edge of a fourteen-inch 

 share, and being thinner stays sharp longer. The disk plow 

 rolls over obstructions instead of catching. These items 

 greatly reduce the cost of repairs, in which should be included 

 sharpening, as compared with moldboard plows. 



The common practice with disk plows is to plow a continuous 

 furrow around the field without lifting the plows. As the disks 

 seldom choke up with trash and do not require frequent sharp- 

 ening, lost time on" account of the plows is less serious. On the 

 other hand, larger triangles at the corners of the field are 

 usually left to be plowed out with horses. In rounding the 

 corners unplowed patches are apt to be left between strips, neces- 

 sitating extra trips between corner and centre to finish the field. 



