Removing the blade can sometimes be the hardest part of the job. A good way to start is to squirt some penetrating oil on the blade bolt and nut and let it stand for a few minutes. While you are waiting, pull the spark plug wire to make sure the mower does not accidentally start. Never work on your mower with the spark plug installed because the engine can unexpectedly, this is especially true when removing the blade as you can easily turn the engine.
Next, block the blade so that it does not turn while you are removing the blade nut. A blade holder will make this easy. However, if you do not have one, a block of wood under the deck and a C-clamp will do the job.
Once the blade is removed, use a scraper to remove excess grass build up. This will enable you to balance the blade properly when finished sharpening.
The primary goal is to consistently maintain the correct angle on the blade. Manufacturers perform hours of testing to determine the angle that will give the user the best cut with the longest span of time between sharpening. It's important to keep the angle as it was intended. Around 40 - 45 degrees is typical, but this can vary, so check with the blade manufacturer to obtain the exact figure.
A narrower angle, such as that of a pocketknife, will cut well initially, but will dull quickly and nick easily. On the other hand, a blade with a less severe angle will not provide the same quality of cut, even though it might wear more slowly.
Blades come from the manufacturer with a milled edge. Milled edges are the best, but machines that provide a milled edge are expensive. You still can do a good job with a professional blade grinder. A sharpener with a grinding wheel is not preferred, because it will give you a hollow grind.
As you sharpen, move the blade back and forth across the grinder, maintaining the proper angle until you get the edge you need. Do not force the blade into the grinder. Forcing the blade to grind faster heats the blade and will cause the metal to lose its temper.
It is not necessary to grind a blade until all nicks are out. Grind until you have a sharp edge on the blade in the area where there are no nicks. A blade with numerous nicks should be replaced, but a few can be tolerated.
Try to grind both edges of the blade evenly, removing the same amount of metal from both ends. This is important when you check the balance. An inexpensive cone-shaped blade balancer can do an excellent job. Wall-mounted blade balances are also available. These help you see if the blade is straight. You can also insert a screwdriver in the center hole and check to see if the blade remains horizontal. If the blade does remain horizontal then the blade is in balance. If one end falls lower than the other then you will need to grind a little more off the lower end. Keep doing this until the blade remains horizontal
An out-of-balance or bent blade can cause severe vibration and damage to your equipment. You can balance a blade by grinding just a little more metal off the heavy end of the blade. However, never try to straighten a severely bent blade. Straightening it could cause a weakened or cracked blade. A cracked blade could break apart when turning at high RPM under the deck. The potential liability or injury is not worth the cost of a replacement blade.
Once you have finished balancing the blade and checking it for straightness, clean any burrs or jagged edges with a metal file. Now it's time to put the blade back on the mower deck. Remember you now have a very sharp blade. Use extreme caution when installing.
A few words about safety Small engines and the equipment they drive can and are very dangerous to work on. Always use your good judgment when working on power equipment. Never wear loose clothing and never rest any part of the machine on your legs or any other part of your body. Read and understand the owner’s manual that came with your equipment. Always remove the spark plug from your engine when doing any type of maintenance. It’s not enough to just remove the plug wire, take the extra step and remove the plug from the engine.
» left by Tony from MA (3 years 115 days ago.)
Yes the article was helpful, but I still have a question and it might sound stupid but here goes!! Which way should you be sharpening, going with the angle or against it Respond to this comment
» left by Outdoor Power Parts (3 years 115 days ago.)
Go with the angle. Just make sure you don't bring the edge to a razor sharp edge. Leaving the edge slightly blunt will make the edge last longer. Respond to this comment
» left by Tony from MA (3 years 113 days ago.)
YES! it was , thank you very much. I'm very impressed with this Respond to this comment
» left by John from Raleigh, NC (2 years 173 days ago.)
This article was very helpful and Thanks for the Q&A which confirmed my 5-7 yrs since last time I sharpened a blade. Cheers Respond to this comment
» left by Sid Irwin (2 years 32 days ago.)
I use a fine wire thru the bolt hole to balance the blade. is this OK? Respond to this comment
» left by outdoor power(3,384) (1 year 183 days ago.)
Most mowers have the standard thread direction, righty tighty.. lefty loosy..however, some do use the reverse. Its pretty easy to tell though, start with turning to the left if it feels like its getting tighter then go the other way. you shouldn't have to turn it more than a half turn to know which direction.
» left by Ziglar from NC (1 year 177 days ago.)
Great Article! Have a question, do you have to use a torque wrench to tighten the bolt when you are done, or can you just tighten it down the best you can? My manual recommended it, but they are almost half the price of the lawn mower! Respond to this comment
» left by Anonymous (1 year 176 days ago.)
Torque wrenches are good to have, but it's just lawn mower. I never use one. Respond to this comment
» left by Anonymous (1 year 173 days ago.)
Thanks for the article. Do you have to have a bench grinder, or can you just use metal rasps/files to get the edge you need? Thanks! Respond to this comment
» left by Joe Hawking from Hawking's Fix-It Shop (94 days 3 hours ago.)
I've always used a file myself. It takes a bit longer, but not much if you have a good file, and you'll also have more control over the entire operation, and be able to obtain a keener edge. A good set of files is far superior to a bench grinder. Respond to this comment
» left by Anonymous from cincinnati (1 year 172 days ago.)
The blade configuration of the new blade i purchased is different than the original blade does make a difference?
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