Appreciating the Plow Coulter

A simple part, the plow coulter, improved the performance of the moldboard plow.

| August 2017

As folks today enjoy “plow day” events in larger numbers, newcomers and old-timers alike are increasingly interested in getting old plows into working condition. While there are many aspects of moldboard plows that I could cover, coulters always seem to be an area in which old plows are deficient.

Coulters (among other parts) are nearly always mangled, mismatched, farmer-fixed or missing all together. In addition to original “factory” coulters, several aftermarket companies – including Lantz, Yetter, and M&W Gear Co. – offered “improved” solutions.

If the word coulter doesn’t ring a bell for you, perhaps you know the piece as a rolling cutter, cutting wheel, disc blade or disc jointer. I’ve heard many different names for the rolling coulter, but they are all (at least in the basic sense) the same thing. The job of the coulter is to cut through trash and open the soil ahead of the moldboard, leaving a clean-cut furrow.

One day while I was working in the shop, my eldest daughter asked what I was working on. After explaining to her that I needed new blades on my plow coulter, as I was in the process of removing the old ones, she said it looked like a big pizza cutter. Ever since, her suggestion of a pizza cutter seems about the most basic way to describe the function of a plow coulter. Imagine trying to scoop up a slice of pizza without first cutting it; plowing in the field is nearly the same. Go without coulters and the field is left much messier than if you would have had them.

Designed to enhance plow performance

The earliest form of plow coulter was actually a sort of standing knife (or a vertical knife edge), which aided in cutting through roots and vines. The downfall of a fixed knife is obvious; it dulls quickly and plugs often. By using a rolling disc blade, plugging was greatly reduced. Most tractor-drawn plow coulters were simply straight, flat blades with smooth edges carried by chilled cone-type bearings (tapered solid iron bearings) inside a forked-type yoke. These commonly used chilled bearings were primitive, but provided long life when regularly greased.

Properly adjusted coulters enable a moldboard plow to do the best job possible and even reduce the draft (amount of power) required to pull the plow. The blades should be sharp and turn freely. Correct coulter adjustment is evident in the open furrow behind the plow by leaving a crisp, clean-cut furrow wall. Adjustment usually involves three factors: for-aft adjustment, lateral adjustment and vertical adjustment. An operator’s manual is an essential resource.