Sharpen Those Dull Blades
Sharp mower blades reduce horsepower and give a clean cut.

The amateur takes his mower blades for granted. The professional babies them. We asked Lyle Grafton, a Plattsburg, Mo., farmer and lawn-service owner, to tell us what he has learned in his 20-plus years of professionally mowing lawns and sharpening blades—the first being the importance of having sharp blades. "Dull blades will tear the grass, not cut it," he says. Dull blades leave a rough cut; you can see streaks in the lawn. They also require more horsepower and therefore more fuel. Dry grass and weedy lawns dull blades fast. Well-watered lawns produce sweet, soft grass that is easier on blades.

Then we asked him for some tips on sharpening.

Safety first. The job is not difficult, but remember to do it safely. You will have to raise the heavy mower deck to remove the blades. Be sure the deck is properly supported so it does not fall on you.

Removing the blades. Most riding-mower blades are mounted with standard threads ("lefty loosey, righty tighty") at between 70 and 100 pounds of torque. To keep the blade from turning as you loosen the bolt, use a block of wood to hold the blade in place.

Blades usually are secured with a bolt, a metal washer, a fiber washer then the blade,followed by another fiber washer. When you reattach that blade, don't overtighten and tear the fiber washers. They are important to hold the blade properly. Replace them as they get worn.

Clean debris and rust. Once you have the blades off (most riding mowers come with a set of three blades), clean them with a putty knife and wire brush.

Straighten blades if needed. Stack the blades side by side to check for bends and twists. Bent blades can easily be straightened with ahammer and anvil. Twisted blades are more problematic. Severe twists can cause vibration and machinery wear. You may have to replace the blade.

Sharpen with a grinder. Grafton prefers a coarse stone to a fine one. A fine stone takes longer to put an edge on a blade. The longer the metal blade is in contact with the stone, the hotter the metal gets and the more chance it has to lose its temper. Always use a stone dresser before sharpening to remove metal filings that may have become imbedded in the stone.

Get the right angle. Manufacturers recommend a blade be sharpened to a 45-degree angle. New blades sometimes have a 30 degree angle, but that is sharper than you need. Besides, if a blade is too sharp, it gets dull more quickly and you have to sharpen it more often. To check your sharpening angle, use a square.

As you sharpen, occasionally dip the blade in water. This will keep the metal cool.

Finish the edge. Once the blade is sharp,examine it for burs and nicks. You likely will have burs on the back of the cutting edge. Remove them with a file. Most nicks areinconsequential; they do not affect blade performance. If you ground all the nicks out, you would shorten the life of your blade.

Check for balance. The last step before reattaching the blade is to make sure it is balanced. Stick a thin (three-eighths inch or less) rod into the hole, and hold the blade in front of you so it can swing.

It should come to rest with both sides level. If one side is lower than the other, it is heavier. A few more swipes on the grinder should bring it into balance. This is important because unbalanced blades create vibration, which can cause mechanical problems with the whole mower. After checking balance, the blade is ready to be reinstalled.

Sharpening Steps:

Tools you will need: protective safety devices for eyes and ears; a putty knife and wire brush for cleaning the blades; sturdy gloves; a square for adjusting the angle of your grinder; a stone dresser; a file for cleaning up burs.

1. Feather the blade against the stone at a 45-degree angle. As the stone and blade heat up, occasionally dip the blade in a bucket of water.

2. After sharpening, check for balance using a thin rod. The blade will dip toward the heavy end if not balanced.

3. Minor nicks in a blade look bad but are not usually a problem. To take all the nicks out, you would have to sharpen it three or four more times, so just ignore them.

By Jim Patrico