HOME CLINIC; How to Sharpen Tools To Their Fine Points
By JOHN WARDE
Published: May 30, 1993
EXCEPT for lawnmower blades and hedge clippers, yard and garden tools are seldom sharpened adequately. Many owners of shovels, hoes and other digging tools may not be aware that the tools should be sharpened.
For sharpening most outdoor tools, all that is needed is a 10- or 12-inch mill-bastard file. For finer-edged tools like pruning shears, also buy a 10-inch smoothing file, and for both tools buy a file card, a type of wire brush for cleaning filings from between files' teeth. Using a file card is a key to keep files sharp.
Before sharpening an edge or blade remove any rust by scrubbing the metal with steel wool or an emery cloth or by applying rust remover like naval jelly. To keep outdoor tools free of rust, mix a quart or two of motor oil, even used oil, with sand in a bucket. After using a tool, plunge it into the mixture several times to clean and lubricate it before storing it.
To sharpen a shovel, clamp it in a vise or to the top of a workbench so that the upper surface of the blade, the side that holds the dirt, is accessible. If you lack a vise or clamps, stand the shovel at an angle against a bench and brace it with your knee. Grip the file by the handle and tip. Then push the file forward and sideways at the same time to file the shovel's leading edge.
It does not matter whether you file from the handle toward the edge or vice versa, but try to keep the file at a uniform angle to the shovel so that a slope, or bevel, is formed. It should be about 70 degrees to the upper surface of the shovel. File with moderate pressure and at an even rate, but let the tool, not your strength, do the cutting. Avoid drawing the file backward over the metal. That can dull the teeth. As the file fills with metal chips or dirt, brush it with the file card and continue.
The bevel should be shiny and of even width. If you are filing from the handle toward the edge, from time to time draw your finger in that direction along the underside of the blade. You should feel a slight ridge of metal, a burr. This forms as the beveled surface meets the underside of the blade, and it is a sign that the edge is sharpened.
When a burr can be felt along the entire forward edge of the shovel, the job is finished. If desired, you can remove the burr by gently filing the underside of the shovel with a few light strokes, but that is not necessary.
Sharpening a hoe is basically the same, but the burr should be filed off when the tool is sharp. Gardeners debate which side of a hoe should be beveled. Conventionally, the side farthest from the handle receives the bevel, and that side is usually the easiest to file, because the handle is not in the way. But some users insist that a hoe cuts weeds more easily if the bevel is on the side facing the
operator. In any case, a hoe used primarily for chopping soil should be filed at an angle of about 80 degrees. Otherwise it will quickly dull.
For trimming weeds, the angle should be about 45 degrees, to provide a sharper edge. Because weeding with a hoe is often done with the tool's corners, some gardeners sharpen the sides of the blade at 45 degrees and the long edge at 80.
File the beveled edge of a mattock to the same angle as the original. Usually that is about 35 degrees to the surface. File the point so that the tip measures about an eighth of an inch square. If either end is chipped or broken, have the tool reground.
Delicate gardening snips and grass clippers that resemble scissors are best sharpened professionally by a scissors grinder or lawnmower center. Amateurs can file hedge clippers and tree-pruning shears. With either tool, spread the handles wide and brace the tool or clamp it in a vise so that the blade to be sharpened is horizontal. Using a smooth file, stroke across the cutting edge toward the blade. Maintain the original bevel or, if the bevel is not apparent, at an angle of about 60 degrees. Remove as little metal as possible, especially near the tip. On pruning shears that cut against a curved bar, square the bar's edges with the file if they have become rounded. You may need a half-round file to follow the bar's upper contour.
Sharpening an ordinary rotary-lawnmower blade, not a mulching blade, is not too difficult if done often enough so that the blade remains well maintained. Some manufacturers advise sharpening blades after every third mowing. If the blade is in good condition, empty the fuel tank, disconnect the spark-plug cable and tape or wire the cable securely so that it cannot spring back against the plug. Doing so could allow the mower to start accidentally. Next, turn the mower on the side opposite the carburetor.
Rotate the blade so that it is vertical. Stand behind the mower in a position to see the blade. Then file against the beveled part by holding the file in one hand while steadying the blade and guiding the tip of the file with the other. The procedure resembles playing a cello. File evenly, counting the strokes. When finished, rotate the blade and file the other end the same number of times to preserve the balance.
To sharpen a neglected blade, remove it from the mower and clamp it in a vise or to a workbench for filing. New blades cost less than $10, and it often makes more sense to replace an extremely dull or damaged blade than to resharpen it. Blades for mulching have curved cutting edges and should be professionally sharpened. To always have a sharp blade, buy an extra one to put on the mower while the other is being serviced.
Diagrams: Sharpen a shovel so that the upper surface slopes toward the edge at an angle of about 70 degrees. Sharpen the bottom edge of a hoe at an 80-degree angle on either side. Empty fuel tank and disconnect spark-plug wire before tilting a mower to sharpen blade. (Edward Lipinski)Source: www.nytimes.com