Lawn Mower Blades

Ronald Strahan, Koske, Thomas J.  |  5/12/2005 11:46:04 PM

Mulch blade (top) vs lift blade.

Cone balancer and wall nail.

Dull blades leave jagged-end cuts.

For a healthy, good-looking turf, you must perform proper mowing. Mowing is what we do most to the lawn. That process removes the food-making structure known as the leaf blade; thus, we must do it properly to avoid excessive stress to the plant.

Simply put, we never want to remove more than the top 1/3 of the foliage in any one cut. When the turf grows back out about 50 percent, then it's time to mow (even if it's not yet Saturday morning). By this rule, we see that lower (shorter) mowing heights will require more frequent mowing. Mowing heights for St. Augustine are 2½ inches in sun and 3 to 3½  inches in shade. Centipede and common Bermuda grasses are best cut to 1½  inches. Mowing at cutting heights of 1 inch or lower is best done with a reel mower.

A sharp mower blade produces a prettier cut with less stress on the turf plant. This requires a fairly sharp mower blade. Sharpening a reel mower blade assembly is difficult and best left to a professional, but sharpening a common rotary mower blade is not a big problem.

Rotary sharpening stones that fit on a hand drill are available. They can sharpen a blade or 'bring out the edge' without removing the blade from the mower housing. These, however, will just do light-duty sharpening and will not allow for balancing the blade to reduce vibration. Plan to sharpen your blade three times a season with zoysia and twice a season with other grasses.

The best way to sharpen a rotary mower blade is to take off the blade and sharpen with a grinder or metal file. When grinding, use eye or face protection and watch out for your loose clothing and sparks. Don't stand in front of the grindstone as it first starts up.

Before working on the mower, always disconnect the spark plug wire. Tilt the mower body to reach the blade, and watch for leaking gas and oil. Chock the blade with a piece of wood so that it can't spin. Remove the blade’s fastening bolt with a wrench or socket. Note the top side and bottom of the blade. Installation is the reverse procedure.

When sharpening the two cutting end surfaces, maintain the cutting surface angle at about 40 degrees. Thinner will be too knife-like and weak; it won't hold up. Thicker angles will be more blunt and will not cut as cleanly. As you sharpen, move the blade back and forth with light pressure. Avoid overheating the steel and losing the metal's temper (hardness). You may cool the steel by dipping it into water.

After sharpening, always check the blade's balance using an inexpensive, cone blade balancer. A nail pivot in a wall or stud can do in a pinch. If the blade leans more to one end, take more metal off of that end's cutting surface to balance it. A balanced blade will vibrate less and cause less engine wear.

Never try to straighten a badly bent blade. Never try to use a cracked blade. If the blade is damaged or the cutting surfaces are worn too thin, replace the blade.

Choose the correct blade type and length for the mower housing and type of mowing you do. Mulching blades have more bends and greater cutting surface than do standard, or high-lift (bagging) blades. Mulching blades are designed to circulate the clippings and cut them several times. Lift blades are designed to cut, lift and blow out the clippings. The high lift creates more suction and air flow to better bag the clippings.

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