How to Sharpen Your Lawn Mower Blades

This is our wheel grinder fully equipped with safety warnings and the last date it was worked on.

Its been a wet and wild spring and summer. This is great news for your lawn but terrible news for your lawn mower. Our grass is the healthiest its been in years, that means a little more maintenance to get you through! We’ve been through the steps to mid season mower maintenance, but in this article we’re going to focus on the maintenance tip that has the most impact on your quality of cut-your blades. We’ll discuss how to know when you should sharpen your blades, how to take them off, how to sharpen them and even how to put them back on to make sure you’re getting the most out of your lawn mower.


When to sharpen your lawn mower blades:

We’ve been saying in numerous blogs that you need to sharpen your blades at least 2-3 times a year, but how do you know when its time? The answer comes straight from the grass itself. When your blades are sharp they will slice your grass thoroughly. When your blades are dull they will tear your grass. These tears leave a white streak behind your lawn mower after you’ve mown. White streaks are the biggest indicator that its time to sharpen the blades.


How to take your blades off:

Removing your lawn mower blades can be a lot easier with air tools. 

Push mower:

Turn your push mower on its side so that the carburetor is facing up. You’ll want to do this in order to keep the gas from flooding the carburetor while you’re working on the machine. Take and impact wrench or a socket and remove the blade bolt and blades
*Hint: This can be a great time to go ahead and clean out under your push mower. Cleaning it allows proper air-flow under the deck, and can help your engine last longer.

Riding Lawn Mower:

Depending on your lawn mower, the easiest way to take the blades off can be to remove the entire deck. Make sure that you know how to put it back on and give us a call if you have any questions. Most decks need to be removed from the side of the machine, don’t try to drive over the deck unless you know for a fact that you can. Once you have the deck off, simply use an impact or socket wrench to remove the blade bolt(s) and blades.

Zero Turn Lawn Mower:

Because zero turn lawn mowers have more complicated deck systems, it is generally easier to lift the machine to a point at which it’s safe to get under the deck and take the bolts and blades out, without removing the deck. A hoist or jack can be the best way to do this, just make sure that there is something around to catch the machine should your hoist or jack give out.

We use a chain hoist to lift zero turns off the ground but a standard floor jack can do just as well. 

How to sharpen your blades:

Once you have removed the blades there are two things you need to consider.

  1.  Structural integrity of the blade
  2. The sharpness of the edge.
  3. The balance of the blades.

1. Structural integrity: This refers to how the blade is holding up. This will indicate whether you need to sharpen the blades that you have or whether you need to purchase a new set. Check the following:

  • The blade edge: Look for cracks or cuts where you might have hit something. Make sure that you’ll be able to grind edge smooth without taking too much off the blade.
  • The blade width. Compare you’re blades to what they looked like new. Typically you start to see wear around the end, you’ll want to be able to grind the edge smooth without making the blade too narrow.
  • The lift wings. Often overlooked, the lift wings are what creates suction under your deck. These can be the one of the first things to wear and the most dangerous if they break. Make sure to look for cracks on the base of the wings.

2. Sharpness: If you find that your blades pass inspection it’s time to move on to sharpening them. A grinder, either in the form a mounted wheel grinder (what we use) or hand grinder can put a sharp edge on your blade. Wheel Grinders are by far the best way to sharpen your blades as you can set your angle and keep it consistent with minimal human error.

Run the blade against the grinder with the stone spinning downward

Make sure to have soapy water on hand so you don't burn the blade

  •  Wheel Grinder: Run the blade against the grinder (the grinder spinning downward) applying enough pressure to grind but while taking off the least amount of metal per pass. Try to maintain about a 30° angle. You’ll want to keep some soapy water around to dunk the blade to keep it from over heating. Grind the blade 1-2 times, then dunk until you’ve reached a sharp edge.
    *Hint: Take a hand grinder and grind the back of the blade on the sharp edge to make for an even better cut. Don’t over grind, just take the excess metal clippings off the back.

  • Hand Grinder: Secure the blade in vice so the edge is facing up. Apply the grinder, taking off as little metal as possible while maintaining a consistent 30°angle. You may want to apply soapy water to the blade to keep the heat down. Continue until you have a sharp edge then spin the blade around and do the other side.

3. Balance: The last step in the sharpening process is to make sure your blades are balanced. This will reduce wear on your machine and improved the quality of the ride and the cut. We use a blade balancer with magnet. They make many tools to do this as well. Feel free to give us a call so that we can direct you to the right tool. Many people use a piece of wood mounted into a nail. This can work as long as you have the blade perfectly centered on the nail. As long as the blade doesn’t spin you can be sure that it’s balanced.

This is the balancing tool we have here at Humphreys to make sure the blades stay centered.

You want the blades to stay level, this blade is not balanced. 

How to put your blades back on:

Clean your blade bolts washers and spacers. Maker sure there is no grass, dirt or mud then coat the blade bolt with an anti seize layer. This can be purchased from your local auto parts shop.

Anti Seize can be purchased from most auto parts stores

Applying anti seize can help make taking your blades off the next time an easier chore. 

Assemble your blades, bolts, washers and spacers just as they were when you took them off. Then start to tighten them. Tighten them with a socket or wrench by hand until you can’t turn the bolt any further. Be sure to consult your manual for the proper torque specs. 

Then you’re done. Make sure that everything is secure and get back out there and start mowing again. If this sounds like too much, go ahead and schedule and mid season tune up, or bring your blades in to be sharpened and we’ll handle everything!