DISK TILLERS
These tools are designed for both tillage and seeding. They consist of a single gang of disk blades, 20 to 26 in. in diameter, on a common axle, all throwing the soil the same way. The common axle differentiates these tools from regular disk plows which have the disk blades tipped back, necessi¬tating separate axles and bearings for each blade.
Disk tillers are made as small as two-blade models cutting 15 in. wide up to models cutting 20 ft wide. They are highly economical of power. Seeding boxes are available for some models, enabling seed-bed preparation and wheat seeding to be done in one operation.
The forces acting on a disk tiller are similar to those act¬ing on a plow except that the resultant lengthwise soil force on the blades is usually upward, requiring extra weight for penetration.
Trail-type disk tillers usually permit the angle of attack of the disk gang to be adjusted from 40 to 55°. In hard high-draft soil, penetration can be improved and width of cut de¬creased by increasing the angle, while maximum width can be taken with less angle in loose easy-working soils. This adjustment is provided by changing the angle of the land wheel and the furrow wheels with respect to the disk gang.
Hitching principles are similar to those for mold-board plows. The centre of draft is at the centre disk blade slight¬ly below the surface of the ground. Disk tillers are necessarily built heavier than mold-board plows and wheel weights can be added for penetration in hard soil.