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April 06, 2018 | Lawn Guides

Recommendations on How to Sharpen a Lawn Mower Blade

Recommendations on How to Sharpen a Lawn Mower Blade

Trimming the excess grass from the lawn is possible even if the edges of the mower blades are obviously dull. However, the shoots will separate in the longitudinal direction, turning into a fringe. A few days after mowing, the grass will become rotten, which will last for a few weeks. The cut must be smooth and neat, then the grass will heal in just a few hours and the lawn will always be juicy-green. This requires the blade to be sharpened almost perfectly.

At first glance, it might seem that it’s easier to replace a dull blade with a new one. But it will lead to expenses and it may be quite difficult to find a blade of the necessary configuration. This option is justified only if there is significant damage to the cutting edges or damage to the blade after colliding with a solid obstacle such as a stone.

More often than not, it is quite easy to restore the efficiency of the knife – all you need to do is to sharpen the lawn mower blade yourself, so there is no need to wonder where to get lawnmower blade sharpened.

Lawnmower blade sharpening or replacement of a lawn mower blade can be easily done at home. Initial skills of working with a hand toolkit will be enough.

Please note that the sharpening technology depends on the type of blades installed on the lawn mower. There are two kinds of mowers used for lawn work – lawn mowers with a rotary knife and push reel lawn mowers with cylinder blades.

How to Remove a Blade from a Lawn Mower

It’s impossible to sharpen the blades without removing a blade. So, first, remove the blade.

Before you start partial dismantling of the lawn mower, you need to protect both the equipment and yourself her. If it’s simple to disconnect the electric mower from the mains, gasoline lawn mowers require preliminary preparation. First, you need to remove the cap from the spark plug. Next, it is necessary to exclude fuel leaks, that is, either drain the tank or put a sealed rubber membrane under the lid and shut off the fuel faucet.

It’s required to turn the lawn mower only towards the handle, unless otherwise explicitly stated in the operating instructions. Before turning the lawn mower, do not forget to squeeze the exhaust hose so as not to spill the oil.

Video – how to remove mower’s blade properly:


Blades of different configurations are used in lawn mowers. Usually, this is an ordinary two-bladed plate of complex shape. However, the blade can also be a composite – the upper blade is intended for mulching the mown grass. There are also four-bladed knives, which can be both composite and on a common base.

The blade can be fastened either with one bolt in the center through a shaped washer or two bolts with a landing on the center hole or pin. In any case, the screw thread is on the right. To lock the shaft from the rotation, place the block under the knife, resting on the ground. It is desirable to memorize or outline the position of the blade (s), in order not to confuse anything when reassembling.

Cleaning and Stropping

When the blade is removed, it is necessary to clean it first of the mud and hardened herbal juice. The easiest way to do this is to use a metal duster. The strip of the blade should be clean from all sides.

Often, solid objects such as stones and chips get into the working area, which deforms the blade very much. Most blades are not straight but the cutting edge and strip at 10–15 cm from it should be examined for the presence of local bumps and curvatures. This is done with a short straight line.

You can straighten the blade with a usual hammer, whose edges are slightly rounded. Put the blade on an even massive support (anvil), then give the correct shape with the weak blows on the metal.

You need to strop the blade starting from the edges of the curved section, gradually moving towards the center. The twisted body of the blades is a small problem but it is very important that the cutting parts are straightened into one straight line. Also, it is necessary to check the throwing blades, which are often unbent from the impact. If the blades are bent at different angles on different shoulders of the knife, this will worsen the air flow and the mown grass will not be properly mulched.

Sharpen with a File Fixing the Descents

If the blade has not been sharpened for a long time, chipped chips are likely to appear on it. You need to get rid of them by removing the edge of the blade at a uniform angle along the entire length of the cutting area. Note that there may be several edges on each side, in this case, several cutting planes are formed at the lawn mower.

Lawn mower blades have one-sided grinding, the descent of which, as a rule, is turned upwards. To bring the descent to the desired angle, you should use an electric sharpener such as Dremel, and in the absence of such a small file. It is very important to remove the metal evenly from both blades. Therefore, hold the same pressure and at least roughly count the number of passes of the sharpener.

Sharpen mower blade

Slight deviations of the angle of sharpening are not critical but the smoother the slopes are, the greater will be the resource of the blade. Using the grinder or the drill for pre-sharpening isn’t recommended – overheating can degrade the quality of the metal.

Sharpening by Hand

The purpose of DIY sharpening is to eliminate small cleavages of the edge and to bring the descent into one straight plane. The presence of a saw on the blade leads to a rapid reduction in sharpness, while with a rounded descent, there is too much impact on the cut stems. In addition, the blade with a rounded shape gets dirty much faster.

The best way to sharpen mower blades is to use a flat emery block with a grain size of about 400–600 grit. Soak the bar in sapwood for 10–15 minutes and periodically moisten during the process.

When sharpening, try to stick to the same position of the stone in order to maintain a constant angle. As in the case of stropping descents, the sharpening should be carried out with the condition that the same amount of metal is removed on opposite blades.

Stropping the Edges

When the blades are sharpened, they need to be corrected. This is done using a piece of moisture-resistant sandpaper with a grain size of about 600–800 grit. The paper needs to be moistened with water and rolled into a cylinder 100–150 mm in diameter.

The stropping is done to remove the slightest burrs and flakes, due to which the thinnest edge of the blade can wrap. The sandpaper sandwiched into the cylinder should be pressed lightly against the plane of descent and stretched out smoothly from the grain. It is also recommended to make a smooth displacement from the center to the edges.

When stropping the descents and sharpening mulching blades, all manipulations are carried out with only one side of the blade. During the process, the blade is also processed from the back side. Here, the paper is pressed almost against the body of the blade but with a slight inclination towards the edge. The pressing force is quite small but a lot of the movements need to be made, seeking to eliminate the large grooves on the brilliant descent that remained after sharpening.

How to Balance Lawn Mower Blades

Before installing the blade back, you need to make sure that its shoulders have at least about the same weight. Otherwise, vibration will occur during operation, which will not affect positively the life of the spindle.

Balancing is carried out mainly for two-sided single and composite blades. The four-bladed blades are not so strongly subject to imbalance. To check the knife, it is necessary to clamp the smooth bar in the vice in a horizontal position. On it, the blade is put through the hole in the center, after which attempts are made to establish it strictly horizontally. If one of the shoulders weighs significantly more than the other, the blade will steadily turn to one side.

The equalization of the weight of the shoulders is carried out by grinding a small amount of metal from the back of one of the blade’s shoulders. It is not necessary to achieve super precise balancing but the blade should stay at least for a few seconds in a strictly horizontal position. When the balancing is done, you can put the blade in place and, finally, update the look of your lawn.

Video on how to balance blades:

How Often to Sharpen Mower Blades?

Mower blades should be sharpened when necessary when the blade gets dull. You will see when it’s time to sharpen the blades – the lawn mower will start working weird or there will be more fuel consumption if it is a gasoline mower.