Push lawn mowers are a great way to cut your grass if you don’t have any other options. The only downside is that the blades go dull over time and need to be sharpened periodically. It’s not hard to do, but it can be an annoyance when you’re in the middle of cutting your grass! The process for sharpening a push lawn mower blade requires only minimal tools and simple steps. We will go over these steps now so you can sharpen your own blades without any trouble!
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When to sharpen lawn mower blades
A trained eye can tell when a blade needs sharpening by simply looking at the lawn after mowing. If the height of the grass is uneven because the mower has not mowed in some areas or if there are cracks in the blades because the blade is dull. But it will be easier for the average homeowner to remember to sharpen the lawnmower blade about every two months. This equates to three times a year in the north for the typical homeowner.
Removing the push lawn mower blade
Before you sharpen the rotary mower blade yourself, you need to make some preparations. One of them is to remove the blade. If you have an older rotary mower, it is usually located directly on the crankshaft. Newer machines have a blade clutch. This decouples the blade from the drive.
Before you remove the blade, pay attention to safety. Make sure that the device cannot be started unintentionally. Some machines start when you turn the blade.
If you have a gasoline mower, disconnect the spark plug. Disconnect electric mowers from the mains before removing the blade. Remove the battery from a cordless mower. Then carefully lay the machine on its side. Gasoline mowers are stored with the air filter facing up. This way, no gasoline or oil will leak out. Place a thick piece of corrugated cardboard underneath to protect it.
The next step is to put on work gloves and remove the blade bar from the mower. Refer to the manual of your push lawn mower. The screws often have a right-hand thread. You loosen them counterclockwise. Some manufacturers have installed screws with a left-hand thread. Therefore, it is also worthwhile to take a look at the instructions.
If a screw is tight, put a little penetrating oil on it. Let it soak in overnight. With a few careful hammer blows on the screw head, the screws will loosen. Do not hit too hard. Otherwise, the crankshaft bearing or the blade clutch may be damaged.
Wedge the blade to the inner housing wall with a hardwood wedge. This will prevent the crankshaft from turning when the bolts are loosened. Place all screws and washers in the correct order. This will make it easier for you to put everything back together properly later.
Sharpening lawn mower blades manually
For the grinding work, you need the right tools. This includes a vice. In this, you fix the blade bar. The vice prevents you from injuring yourself while sharpening. It also makes it easier to adjust the grinding angle.
Use hand files of different thicknesses. This way you will achieve a precise sharpening. Hand files are also suitable for inexperienced sharpeners. They allow you to grind slowly and in a controlled manner. This makes it easier to correct any errors.
Experienced craftsmen use a sanding file after rough sanding. This allows you to work more precisely. Finally, you pull the knife over a whetstone.
Use hand files to sharpen the rotary mower blade. Use files with different thicknesses.
Sharpening lawn mower blades electrically
If the blade is badly worn or the work is too strenuous for you, there are power tools that will help you. For example, a wet grinder with a clamping device and speed control is suitable for sharpening.
If you are a skilled craftsman, you can also use grinding finger attachments for multitool devices. But don’t use an angle grinder to sharpen your push lawn mower blade. This has many disadvantages. For one thing, it is difficult to guide. In addition, you remove too much material at once. The blade also heats up a lot. This is due to the high speeds. The high temperatures “burn” the soft steel. The blade turns black. As a result, it loses its elasticity.
Dry and fast rotating grinding stones are also unsuitable. They also generate too much heat.
Knife sharpening guide
Once you have removed the knife, clean it roughly. This gives you a good view of the cut surfaces. Then clamp it in the vice. The blade bar lies horizontally with the wings pointing upwards.
Sharpen the lawn mower blade only from above. Do not work on the underside. Keep as close as possible to the specified cutting angle of the blade. Use a coarse file to remove old burrs and other damage. Then sharpen a new cutting edge in the sides of the knife. Rework the cut edges with a finer file or a grinding file.
Remove equal amounts of material to the left and right of the knife bar. This keeps the knife in balance. You can check this with a trick: Place the knife bar with a center hole on a screwdriver. Alternatively, place the bar in the middle on a spike or a small elevation. If the bar tilts to the side, remove some material from the heavier side.
The balance is important, otherwise, an imbalance will occur at high speeds. This causes the crankshaft bearing to wear more quickly. You will also feel strong vibrations when mowing.
Finally, you drag the cut edges over a grindstone. If the blade is covered with rust spots, remove them with a wire brush. Brush it over the cutting edge to remove the stains. Then reinstall the push lawn mower blade. The blades will be facing up. The flat, unsharpened side is at the bottom.