The disk-plow bottom is a perfectly round, concave disk of heat-hardened steel, sharpened on the edge to aid in the penetration of the soil. The size of a disk-plow bottom is the diameter of the disk and ranges from 20 to 38 in. the average thickness of the steel for disk-plow bottoms is 4.8 mm for the smaller sizes and may be as much as 9.5 mm for the larger sizes.
Angling of disk-plow bottoms The disk bottom is attached to a standard which may extend downward from the heavy steel beam. The disk rotates on a chilled-iron ball or roller bearing. The standard is adjustable to give variable degrees of vertical and horizontal angle to the disk bottom.
The disk plow can be made to penetrate more easily when the disk is set more in a vertical position. The flatter it sits, the less tendency there will be for it to penetrate. Further to enable the disk plow to take the soil properly, weight is added to the frame and wheels to force the plow into the ground. There is one great difference between moldboard and disk plows: the moldboard plow is pulled into the ground by the suction of the plow, while the disk is forced into the ground by added weight or force and by the suction of the disk due to the angle at which it is set.
The horizontal angle of the disk influences the width of the furrow slice and tendency to roll. Disks set more nearly perpendicular to the direction of travel cut wider furrows and don’t turn so freely as those set more nearly parallel to the furrow. The top of the disk is revolving to the tractor operator’s left. The furrow slice is pulverized to some extent when carried over the concave surface of the disk.
The center of resistance the center of resistance on disk plows is closer to the furrow wall than on moldboard plows. Its location is to the left and below the center of the disk. The exact point varies with the vertical and horizontal angles, the depth, and the amount of concavity of the blade.
Accessories for disk plows
Disk-plow bottom should be equipped with scrapes which can be adjusted to work from the center to the edge of the disk. With the aid of the scrapper , it is possible to get greater pulverization of the furrow slice. It is also possible to invert the furrow slice and cover trash much better. Weights aid in forcing the disks into the soil and hold the wheel in the furrow to prevent the disks riding out of the soil when plowing extra-dry and hard soil. Most types of disk plows can be obtained with hydraulic lifts. Levers or screw cranks aid in leveling the plow and adjusting for depth.
Wilkes, smith. Farm machinery and equipment. TMH edition