Project Engineers, John Deere

Worldwide Commercial & Consumer Equipment Division

Reels are typically configured with five-, seven- or eight-inch diameter reels and have either five, six, seven, eight, 10 or 11 blades on each reel.

For commercial grounds care professionals, whoever can cut the most grass in the least amount of time with the desired finished look wins the game. Choosing the right mower for the application - be it a walk-behind, wide-area front mower or a greens mower - is certainly a step in the right direction. But having the right machine coupled with the right cutting unit is what will ultimately keep you on top. Below is a quick overview of the primary cutting systems, how they work and how to care for them.

Reel Mower Systems

Reel mowers are used most often in golf and sports turf applications because they can closely follow undulations when cutting grass at a height of one and a half inches or below without scalping the turf. The clean, precise cut of a reel mower lessens the chance for grass to become susceptible to disease and fungus.

A reel mower system is made up of three main components - the reel, the bedknife and the roller. The reel itself is a series of blades with sharp edges. The bedknife, which has an edge with a five-degree relief angle on the front and a five to 6.5-degree angle on top, creates the shearing edge. The combination of the reel and bedknife takes grass in and shears it much like a pair of scissors cuts paper.

Reels are typically configured with five-, seven- or eight-inch diameter reels and have either five, six, seven, eight, 10 or 11 blades on each reel. The lower the number of blades usually means mowing at a higher level of cut. For instance, five blade units are most often used for intermediate or rough areas where the height-of-cut is approximately _ inch or higher. These reels have a low frequency of clip, which is required for applications involving cutting taller stands of grass. At the other end of the spectrum, 10- and 11-blade units provide a much finer cut and are ideal for tees, approaches and collars.

Bedknives can come in a couple variations depending on the application. A standard bedknife is used for regular fairway mowing and can cut down to 3/8 inch. Tournament bedknives can cut down to .1 inch. Some manufacturers now offer ultra-low tournament bedknives for cutting grass to .078 inches for use on Hybrid Bermuda and Bentgrass greens.

Reel mower systems use rollers to control the height of the bedknife from the ground and determine the height of cut. Several types of rollers - smooth, grooved and spiral grooved - are available to use depending on desired cut finishes and mowing conditions. Smooth rollers will give a neater appearance and can follow ground contour without scalping. A grooved roller helps stand grass blades straight up for an even cut. Spiral-grooved rollers allow reels to pass through small stones or acorns without getting caught and scaring the turf. Spiral rollers also help remove excess thatch.

Within the reel mower system family, there are a few variations - one of which is the is the vertical cutting unit. This system consists of a set of vertical disks with cutting edges. They are designed for vertical cutting to eliminate runners, promote new growth, dethatch and expose soil surface for overseeding applications.

Consumer walk-behind and some smaller commercial walk-behind mower decks with a cutting width ranging from 18 to 22 inches usually have a single-blade configuration. Most commercial decks have either a two- or three-blade configuration.

Since reel mower systems provide for such precise cutting, sharpening and maintaining these systems must also be a precise process. Sharpening a reel mower system is a three-step process. First, spin-grind the cylinder to "true it up" so that one end of the reel cylinder is not larger than the other. Also, as the blade wears, a radius is made on the cutting edge, so it’s important to grind the blade to get that sharp edge back. Once that is complete, a relief grind is the next step. Relief grinding is a blade-by-blade process where the blade is beveled back 20 degrees. This 20-degree bevel provides the relief necessary to create a place for the grass to be cut without pinching. Reel sharpness can be maintained by grinding or backlapping at regular intervals, and cut quality can be maintained on a continuous basis by backlapping. Backlapping is actually sharpening the blades in a reverse spin as if sharpening a pocketknife for a clean edge. Most manufacturers recommend backlapping every 25 to 35 hours to maintain a sharp edge on both the bedknife and the reel. On greens where an operator is mowing with a lot of topdressing, backlapping may be required as much as every 10 hours.

Rotary Mower Systems

Rotary mowing systems are the most common and have the broadest applications. When buying rotary mower blades, one of the most important things to remember is to look for those that have been designed to perform for the specific mower in question. Using blades in an application that they were not specifically designed for may actually decrease mowing effectiveness or even be unsafe.

Rotary mower blades can be divided into two broad categories - side- or rear-discharge and mulching. However, the primary function of most rotary decks is side discharge. The blades on these decks have a more aggressive wing and higher airlift so they propel grass out the side discharge chute more efficiently and disperse the clippings more evenly.

Mulching blades typically have a downdraft feature inboard from the airlift that directs materials back into the turf. Recently there has been increased interest in blades with short notches in the airlift portion, which can cause more shredding of the cut grass but generally does not improve cut quality or dispersion.

Rotary mowing systems are often configured with single, two and three blades. Consumer walk-behind and some smaller commercial walk-behind mower decks with a cutting width ranging from 18 to 22 inches usually have a single-blade configuration. Most commercial decks have either a two- or three-blade configuration.

Blade sharpness is the essential element of mower blade maintenance. Sharp blades require less power, give a cleaner cut and do not fray the end of the grass blade (which results in grass tips browning). Mowing conditions and hourly use determine when to sharpen blades. Generally, if blades are cutting lush, thick lawn areas, they may only need to be checked once during the middle of the season. If the mower is being used on an all-day, everyday basis, the blades should be checked every 25 to 30 hours. If the blades are cutting in areas with sandy soil conditions, the blades should be checked more often.

Most manufacturers recommend that certified technicians sharpen mower blades. However, if you do this yourself, you can use a grinder, hand file or electric blade sharpener. Keeping the original bevel, the blade should have a .40mm (1/64 inch) cutting edge. Make certain to file a uniform edge to ensure a clean, even cut.

After sharpening and during reinstallation, it’s important to remember to properly balance them. An unbalanced blade causes vibrations and movement in the deck that can lead to premature part failure and possibly unsafe mowing conditions. A balanced blade helps to ensure even cut quality, lower sound levels and increased operator comfort.

To balance, place the blade on a nail in a vice or vertical wall stud. Turn the blade to a horizontal position. If the blade remains horizontal, the blade is balanced. If one end drops, grind the bevel of the heavy side and rebalance. Repeat the process as necessary until the blade is balanced.

Damaged or bent blades are inevitable for any mower deck. To check for a bent blade, lower the mower on a flat surface and measure the distance between one end of the blade tip and the ground. Turn the blade 180 degrees and measure the distance between the blade’s other tip and the ground. If the distance between the two measurements is more than 3mm (1/8 inch), it is time to install a new blade.

A blade should be replaced when it is either bent or is substantially worn from either resharpening or sandblasting. When operating in areas that have sandy soil, the airlift portion of the blade may wear away more rapidly as the sand erodes the blade material even though there may still be material left for sharpening the cutting edge. If the cutting edge has been sharpened enough to move it back more than _ inch to 3/8 inch, it should be replaced.

No matter the blade type, it’s important to remember to handle blades carefully to help prevent injury. Always use gloves when handling blades. Keep the factory-installed chute guards intact and in the proper position, and avoid mowing areas with hidden obstacles that can damage the blades.