How to sharpen lawnmower blades with a grinder, step by step:


Lawnmowers are the machines of choice for maintaining your lawn. But over time, the blades get worn out. If you notice some uncut patches or uneven cut grass, the blades are probably dull. Of course, you replace the blades, but this is often not needed. You can sharpen them at home with some simple tools like a grinder in less than 15 minutes. This blog post will explain the involved steps.

How to sharpen lawnmower blades with a grinder, step by step Step

  • Step 1: Gather the necessary tools
  • Step 2: Inspect the blades
  • Step 3: Remove the center nut of the blade carefully and clamp it
  • Step 4: Set the blade and edges and prepare the angle grinder
  • Step 5: Run the angle grinder along the edges of the blade
  • Step 6: Align the angle grinder disk with blade angle
  • Step 7: Sharpen and polish the beveled edges
  • Step 8: Balance the blade, grease it and fix it back

For all types of lawnmowers the blades are located at the bottom of the machine. Most powered mowers have a single set of double-edged blades. The blades can get dull if used for an extended period or after hitting stones, dirt, and water. A lawnmower loses its efficiency if its blades are not in their prime condition. Sharpening them in due time will help prolong their life too.

If you feel like taking up the job yourself without the help of an expert, the following article includes all the necessary steps and precautionary measures to help you do so.

How to sharpen the lawnmower blades with a grinder

Sharpening your lawnmower blades with a grinder involves several steps.

● Step 1. Gather the necessary tools:

Using the right tools for the job makes the work easier. The following tools are needed for sharpen the lawnmower blades with a grinder:

  • A pair of safety goggles and gloves.
  • Wrench set
  • An angle grinder
  • Clamps
  • Piece of wood
  • A bench vise to clamp the blades.
  • Plastic bag
  • Wire brush
  • Sandpaper

● Step 2. Inspection of existing mower blades:

The first step before starting the sharpening process is to disconnect the sprak plug cables. This prevents unintentional starting of the engine. Also apply the parking brakes.

Lawnmower blades usually need sharpening after 30-40 hours of usage, depending upon the quality and usage. It is important to check the lawnmower blades to better understand the extent of damage and then decide whether sharpening is the way to go, or if blades need to be replaced.

To examine the blades you need to access under the lawnmower. Depending on the type it is easy or difficult to tip the mower on its side. If you have a heavy sit mower a lawnmower lift can make this part much easier. To prevent any fuel leakage, you should close the fuel valve (if available), or remove the gas from the gas tank.

Inspect the blades. Look out for rough edges of the blade. Try rotating the blade to check if there is any play or hindrance offered to the rotation. Make sure to have your safety gloves on while inspecting. Check for any severe cracks or presence of rust. Mark your blade on one side, so you know which way to reinstall it. If you notice severe damage you need to replace the blade.

● Step 3. Remove the center nut of the blade carefully and clamp the blade

To remove the blade loosen the nut at the center of the blade with a socket wrench. If you notice that it is difficult to loose, spray the nut with some cleaner spray like WD-40 and wait few minutes. If the blade rotates while removing the nut, clamp a piece of wood to the lawnmower’s underside with C-clamps. After removing the nut, remove the blade from the lawnmower body.

Place the blade in a bench vise and tighten up as much as possible to hold it firmly in place. The blade comprises two cutting edges on opposite sides of one long piece of metal. You will have to work on each turn by turn.

● Step 4. Set the blade and edges and prepare the angle grinder

Wipe up all grass, dirt, and debris from the blade with a stiff wire brush. Rub the blades with sandpaper if you cannot clean all the dirt and debris with the wire brush.

Adjust the angle grinder with a metal grinding disk. You may sharpen it prior with a sharpening stone. The metal grinding disk comes with other complementary tools like a polish disk, buffing disk, and cutting disk. However, they come in later. Make sure you have the blade edge at the top and have some thick safety gloves on. It is also advisable to wear goggles while operating the tool.

● Step 5. Run the angle grinder along the edges of the blade

Now hold the grinder above the blade so that it is at some angle with the cutting edge. Now, turn on the grinder. First, you have to run the grinder along the edge, thrusting it to the insides. Start from the tip and move to the central non-sharp part. Repeat the process along the length of the blade edge for both sides of the blades.

Make sure that your grinder angle is adjusted to the cutting edge angle. Rub the central part of the rotating grinder blade with the blade gently so that you only chip off the rough, uneven metal and cause no cracks.

● Step 6. Align the angle grinder disk with blade angle

Align the angle grinder disk with the blade’s angle from the inside. Notice that this step is opposite to the previous step and must come after it. This step is done to sharpen the edge and set the cutting corner in proper shape. With gentle thrusts from the center of the blades to the cutting tip, carry out the process along the whole length. The outcome will be a sharp, finer blade that has a defined cutting edge.

● Step 7. Sharpen and finish the beveled edges

The finishing steps include running the grinder side by side along the beveled edge of the blade. A shiny, scratch less surface is the indication of a smooth blade. It is important to note that the grinder is used to smoothen the surface evenly. It is a powerful machine, so going deep on one side and remaining shallow on the other is common. Avoid this to keep the blade balanced.

The final step is to polish the edges. Remove the metal cutting ring and attach the polishing and buffer rings turn by turn. Repeat the same steps with a different tool to finish the blades. This will help to prolong their lives and remove any scratches caused by the grinder.

● Step 8. Balance the blade, grease it and fix it back

To avoid wear and tear it is important that the blades are balanced. You can check the balance by hanging it horizontal on a nail on the wall. If it is balanced it will stay horizontal. If not balanced corectly it will move down at a certain side. The side that hangs down is heavier and needs to be grinned a little bit more. When the balancing is done you can lubricate the tightening nut and the fresh edges with some lubricating gel. Using the mark you added earlier you can put it back and tighten the nut.

Reattach the spark plug cable and start the mower engine. Let it run for a few minutes and check if there are no strange noises are heard. If all looks ok it is time for a test run.

Additional Tools

Using a bench grinder to sharpen the lawnmower blade works efficiently. The process is similar to the process above. A bench grinder reverses the process. Instead of moving the grinder over the blade, you move the blade across the grinder wheel.

Frequently asked questions

1. What is the best angle to sharpen a lawnmower blade?

Sharpen the mower blade’s edge using a 10-inch file or an angle grinder, keeping the file or a grinder at roughly a 45 to 60-degree angle with the cutting edge. The angle may vary for some models. Check the user manual before performing the sharpening. It should contain the specifications of the blade’s cutting angle.

2. How many times can you sharpen a lawnmower blade?

A mower blade should be sharpened after around 30 to 40 hours of use. Depending on the uage and type of grass. You can roughly sharp your mower blades at least 2 to 3 times before replacing them. If the blades has hit stones or other sharp objects it can be even less.

3. Can a mower blade be too sharp?

Mower blades should be aggressively sharp but not as sharp as a razor’s edge. You should be able to touch the blade with your hand without getting cut. Additionally, lawnmower blades that are too sharp get duller, faster, resulting in sharpening more frequently and a shorter blade life.

Final remarks:

Lawnmowers, like all machines, require regular maintenance, especially their blades. They cut through tough, dry grass, so they are likely to get dull over time. Angle grinders provide one of the most efficient and fastest ways to remove out rough chips from the blade and reestablish a sharp edge. The article provides you with the key technique involved with using a grinder to sharpen the blades. The edges should be made smooth and properly defined. We hope that you can do the task easily at home by following the steps without going to a professional.

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