Sharpening mower blades can be DIY job
Late fall can be an ideal time to sharpen lawn mower blades. They're nearly always dull and dirty then. Besides, sharpening is a chore gardeners can do early, so they'll be ready to go when the weather warms up again.
"With a few safety precautions, many do-it-yourselfers can handle the job. It's fairly straightforward. The steps are always much the same, even for riding mowers," said Ward Upham, horticulturist with Kansas State University Research and Extension.
In fact, the main difference among today's various approaches to the job is simply the tools people choose to use, Upham said.
A surprising number of DIY-ers still like the control of using a hand file, he explained. Some use a Dremel-type tool or electric drill with a grinding attachment. Nowadays, however, many prefer such power tools as a bench grinder or hand-held angle grinder.
The wrenches they use can vary just as widely, as can the devices chosen to hold and then balance the blades. For example, some homeowners buy a gadget designed to help in balancing blades. Others hang the middle of their sharpened blade on a nail and check whether the blade will balance (i.e., it has equally heavy sides).
Upham warned, however, that before they begin sharpening, DIY-ers must take several steps:
1. Make sure the mower cannot accidentally start up. Unhook or remove the spark plug and/or the battery. Check twice that all power controls are off.
2. Follow your owner's manual directions and expose the mower blade(s), noting what the top and bottom look like, so you can replace them in that position later. Also note whether the blade is supposed to have bends, curves (typical on mulching mowers). To get this done, you may have to tilt over a walking mower, watching out for oil or gas leaks. Or, you may have to remove the blade-holding deck on a riding mower and turn it over.
3. Use a block of wood or a couple of adjustable-jaw wrenches (spanners) to chock the blade in place. People have lost fingers when a blade slipped as they were trying to remove it.
4. Preferably with a socket (ratchet) wrench, remove the nut, washers, etc. that are holding the mower blade against the deck. If you need extra torque for a tight nut, use a breaker bar, possibly including a wrench handle-extending pipe. Number the pieces as you go, especially if you have any doubt that you'll remember what goes back where.
5. Remove and check the blade for damage. If you can't fix it, you'll need to replace it. You may be able to do something, for example, about most nicks. In practical terms, however, a cracked or bent blade is scrap metal.
6. Clean away grass and debris with a moist cloth. Dry before going on.
7. To increase your odds for success, fix the blade in a vice or other stable holding devise.
8. Put on eye or face protection and be ready to watch out for loose clothing and sparks.
"After that, sharpening is simply a matter of trying to duplicate what the manufacturer did originally," Upham said. "Follow the angle of the cutting edge that's already there. Make the same number of passes on both sides, to keep things even. Particularly with a grinding wheel, avoid overheating the blade, because that can cause a loss in temper (ability to hold an edge). Keep grinding or filing until the edge is 1/32 inch--about the size of a period or pencil lead."
Creating an angle that's "thicker" than the original will simply make the blade blunt--even less able to cut cleanly, he said. But, working for a "tighter" angle and knife-sharp edge during sharpening will weaken the blade plus sometimes result in the edge's curling during mowing, leading to a poor quality cut.
To check whether a newly sharpened blade will turn without vibrating and causing unnecessary mower wear, the next step is to check its balance, then make any needed corrections with grinder or file. Inexpensive cone-shaped blade balancers are available at most hardware stores. A nail in a wood stud also can do the job.
"For optimum winter storage, you can finish up by cleaning the blade with solvent or oil, much as you would when cleaning a gun. Don't use water as a substitute; water promotes rust," Upham said. "Then you'll start working in reverse, getting all of the parts and pieces back in the correct place.
"Just be sure everything is fastened tightly enough to operate safely when the grass greens up again next spring."