Disc Harrow

Overview

A disc harrow is a towed tillage implement that prepares ground for planting by slicing through surface residue and stirring it into the topsoil. Rows of concave steel discs, set at an angle to the line of travel, cut the soil, lift and turn a thin slice, and drop it back broken up. Run after harvest or before drilling, it chops stubble, levels ruts, and mixes trash and soil into a rough seedbed. Like a Seed Drill or a Disc Harrow's sibling tools, it is a draft implement: the tractor supplies all the force through the Hitch, and the discs are turned only by their grip on the moving soil, there is no driven shaft.

Because the discs are angled, they generate a large sideways thrust, so the machine is built heavy and braced. Weight is part of the design: the harrow has to press the discs into firm ground, and many models can be ballasted to cut deeper.

How it works

The working elements are the Disc Gang assemblies. Each gang is a line of concave discs threaded onto a common square axle, held apart by spacer spools and clamped into one rigid unit by an end nut; the whole stack turns together on sealed bearings carried in hangers bolted to the Main Frame. As the tractor pulls the tool forward, soil resistance spins the discs, and their concave, angled faces slice down and roll a ribbon of soil sideways.

How aggressively each gang works depends on its angle to travel, set by the Gang Angle Adjuster, a hydraulic cylinder and linkage that swing the gangs from nearly straight to a steep attack angle. A tandem harrow uses two opposed sets of gangs so the side thrust of the front gangs is cancelled by the rear, and the field is left level. The Transport & Depth Wheels raise the frame clear of the ground for road travel and, lowered partway, gauge the working depth in the field.

Wet, sticky soil tends to pack onto the disc faces and stop them cutting, so the Scraper Set rides spring-loaded blades against each disc to wipe it clean. Springs through the frame and scrapers let individual elements ride over rocks without bending, and the folding wing frames bring the wide tool down to road width for transport.