Appreciating the Plow Coulter

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

Properly adjusted coulters.

Properly adjusted coulters.

Photo by Tyler Buccheit

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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.

The gold standard for coulters, which were historically offered by equipment companies, was a simple straight blade. If farmers wanted something better for high residue conditions, straight notched blades were usually the only option. Notched blades helped cut through heavy trash, but of course were less than desirable in rocky field conditions, as rocks tended to wedge between coulter blade notches and the plow share/bottom.

The single dished coulter

As early as the 1940s, aftermarket coulter options began to appear. Both the Lantz and Yetter companies offered aftermarket options early on; M&W Gear Co. entered the market in the 1950’s. While those manufacturers’ designs were distinctly different, each utilized concave disc blades carried by dust-proof, tapered Timken roller bearings. Precision roller bearings reduced drag as well as the need for constant greasing required by traditional designs.  

Yetter’s design was simply a dished blade carried on a spindle sealed with long-lived Timken roller bearings. The coulter attaching arm clamped tightly to the plow round coulter shank. An additional clamp was added to the top of the shank to ensure the side pressure created by the disc blade wouldn’t cause the shank to turn inside the plow frame clamp.

While a coulter at heart, Yetter’s offering was marketed as a disc jointer. A jointer is an aide (usually in conjunction with a straight coulter blade) shaped like a miniature moldboard to assist in turning under trash ahead of the furrow slice. Replacing the jointer (which has a bad reputation for plugging in the field) and straight coulter with one dished assembly would have made the piece an easy sell for an equipment dealer.

The one main drawback to a single dished coulter blade is that it can add an undesirable amount of side draft that can make a plow pull crooked. From experience, I can say that there is a trick to making the Yetter disc jointer work properly, but once set, the Yetter is a real joy to use. When set properly and with good blades, these coulters can cut right through residue with ease while leaving a cleanly plowed field.

The Trash Master Coulter

The Lantz approach to coulter design featured two blades. One large straight blade (17 inches in diameter) sliced through trash with help from a smaller (13-inch diameter) shallow dished blade set at an angle. The beauty of the Lantz design was that any side draft created by the small dished blade is negated by the large straight blade acting as a stabilizer. Both the angle and depth of the smaller dished blade were adjustable to ensure proper function in varying conditions (and to compensate for wear on the larger blade).

Lantz Kutter Kolters found on plows today are often missing the smaller disc blade (most likely discarded) and have been used as a straight coulter only. These parts were obsolete for many years but have recently become available again. From personal experience, the Lantz coulter design – with may adjustments – may seem daunting at first, but once set properly is virtually unstoppable and will ensure a very crisp furrow wall and clean plowing.

M&W Gear Co. began offing heavy-duty dished coulters in the 1950s and continued for several decades. The M&W design was by far the most heavy-duty of any of the aftermarket coulter options. Marketed as Trash Master Coulters, it was available with blades sizes up to 22 inches (according to plow frame clearance). The M&W flat bar mounting arrangement with shear bolt protection was an excellent remedy to the vulnerable round shank OEM coulter design that often resulted in broken shanks. Trash Master Coulters were some of the best available from either aftermarket manufacturers or factory equipment.

After years of aftermarket coulter competition, the OEM’s figured out that customers wanted more options and began offering improved versions. Eventually the most deluxe coulters would be large concave disc with spring-loaded arms for non-stop plowing in even the worst conditions. Toward the end of the moldboard plow era in the late 1970s, most heavy duty plows of all makes came standard with spring-loaded coulters that ensured little chance of damage from obstructions such as rocks, driftwood or tree roots. Improved coulter offerings from original equipment manufacturers led to the decline in popularity of and demand for aftermarket coulters. FC


Plow enthusiast Tyler Buchheit lives in southwestern Illinois. Email him at tyler@mrbtractors.com; visit his website at www.mrbtractors.com.