Mower Care

How to Sharpen Lawn Mower Blades

A dulled lawn mower blade can cause a range of issues in your garden, even putting your grass at risk of disease. It’s essential then to ensure the consistent upkeep of your lawn mower, sharpening its blade regularly. In this guide from Sims Garden Machinery, we’ll take a look through the reasons you need to sharpen a lawn mower, the frequency with which you should look to sharpen, and the techniques for sharpening the blades of various lawn mower designs. This can help you to maintain an effective lawn mower, and a clean, healthy garden.

Why Do You Need to Sharpen Your Lawn Mower Blades?

Dull lawn mower blades can cause both aesthetic and health issues with your lawn. A dulled blade can leave turf with a brown or ragged look, leaving your garden visually unappealing. It can also put your grass in more serious ailments. This is because a sharpened lawn mower blade will cleanly cut through grass blades, whereas a dulled one will pull and tear at it, promoting fungal growth and lawn diseases. This can obviously have long term consequences for your lawn, which can be difficult and time consuming to remedy. As explained in our yearlong guide to lawn care, regular effective mowing is vital for a healthy, beautiful lawn.

When Should You Sharpen Lawn Mower Blades?

There are different schools of thought on how often you should be sharpening lawn mowers blades, but a good rule of thumb is to sharpen them roughly every 25 hours of use. If you are merely maintaining a small lawn every few weeks, then this would mean you won’t need to sharpen your blades very often at all, but those working with larger gardens, or looking to have the perfect lawn may hit that number far more regularly. 

How Many Times Can You Sharpen Your Lawn Mower Blades?

With careful maintenance, you should be able to sharpen your lawn mower blades several times. When sharpening, check the blade over each time, looking for cracks, wear, and damage. Once you see any of these it may be time to invest in a new blade.

How to Sharpen Your Lawn Mower Blades

Closeup of plastic lawn mower drive-wheel with drive gear teeth completely destroyed. Sharpened lawn mower blade in background with nuts bolts tools all on wooden workbench.

There are several different types of lawn mower blades, with rotary being the most common. Other options will be for various types of cylindrical mowers, like reel mowers and manual lawn mowers. There will be a slightly different method to sharpen both of these.

Always Remove the Spark Plug

An absolute essential before you handle the inside of your lawn mower is to completely disconnect the power source. A lawn mower blade when activated can cause a serious injury to anyone currently handling it. All powered lawn mowers will have a spark plug, which when disconnected will mean the mower is not at risk of accidental starting. This will typically be on the front or side of your lawn mower, but if in any doubt check the manufacturers’ guide. Wearing heavy gloves whilst handling your lawn mowers blades is also essential. A lawn mower can be a source of great injuries, making it vital to fully disconnect it from power before removing the blades. 

How to Sharpen Rotary Lawn Mower Blades Manually

Parts scattered on workshop floor with lawn mower on side exposing disassembled cutting blade drive belt and damaged gears on front wheel.

  1. You’ll have to turn your rotary mower onto its side to access the blade. While this won’t be an issue in an electric model, in petrol models you will have to be a bit more careful. Before tipping your mower, determine the location of the fuel tank (or gas tank for Americans), tipping the lawn mower at such an angle that the fuel tank faces up. This will reduce the risk of fuel spilling onto the rest of the mower.
  2. Remove the blade. You’ll need to use a long-handled wrench or a spanner to loosen the blade. Depending on the model of your lawn mower, the method may be slightly different. It can be a good idea to leave a mark on the underside of the blade, using tape or a permanent marker, to ensure you re-install it the correct way round.
  3. To sharpen by hand, first clean your blade, removing all dirt and cut grass debris. Clamp the blade within a vice. You should use a flat hand file to sharpen it, moving from the inside of the sharp edge to the outside. Maintain the current angle of the blade, which is likely to be around 45°. You should be looking to have a shiny, clean edge to your blade. It does not need to be especially sharp, with a butter knife representing a suitable level. Once you have done the first side, flip the blade over and sharpen the other. When both sides are sharpened, balance the blade over its centre, ensuring that it is evenly balanced. If not, you’ll need to sharpen further on one side to restore the balance
  4. Reinstall the blade within your lawn mower. Use WD-40 on the bolt to avoid it rusting over time. Make sure you install the blade the correct way round.

Sharpening Rotary Lawn Mower Blades With a Machine

The rotary lawn mower blade sharpening process can also be accomplished with a bench grinder or belt sander. You should wear a full range of protective gear, including glasses, gloves, and a mask while doing this. In both cases you can hold the blade against the belt, moving it back and forth at the correct angle. If using a machine to sharpen a blade, you should place it within water when hot. The high heat that comes with using a friction sharpening machine can cause the blade to warp. Cooling the blade and drying it can help to avoid this. Another option is to use a power drill with a specialist filing head, combined with a vice.

How to Sharpen Cylinder Lawn Mower Blades At Home

Various lawn mower models have cylindrical blades, such as manual lawn mower blades, or reel lawn mower blades. The best at-home method for sharpening a cylindrical lawn mower is backlapping. This involves applying paste or sharpening compound to the cutting edges of all blades in a cylinder, then running the blades backwards. This technique can give additional sharpness, but for a fully sharpened cylindrical lawn mower you will need to take it to a professional sharpening service. There are also sharpening kits available for cylinder lawn mowers, which can offer another at-home method.

Can You Sharpen Lawn Mower Blades Without Removing Them?

You can backlap a manual lawn mower, or other models with cylinder lawn mower blades, without removing them. For rotary lawn mower blades, it is possible to sharpen them in place, securing them within the lawn mower and then sharpening the edges with a file or angle grinder. But most professionals would recommend removing the blade to ensure a consistent sharpening. 

Where Can You Can Get Your Lawn Mower Blades Sharpened

Whether you have a more complicated cylinder model, or are simply looking for a professional sharpening, professional lawn mower sharpening is available. Sims Garden Machinery are able to sharpen your lawn mower blades from our Stratford Upon Avon HQ. Simply bring your mower along to our shop and our skilled team will be able to restore it to full working order.


Our Comprehensive Range of Lawn Mowers For Sale

Sims Garden Machinery has a huge range of quality lawn mowers for sale through our website, from brands like Honda, Ariens, and Husqvarna. Whatever you are looking for in a lawn mower, we have options; Professional or personal, ride-on or walk-behind, electric or petrol, we can deliver it across the UK. We assemble and demonstrate all products with delivery, ensuring you have a quality lawn mower that you know how to operate. If you’re looking to buy a new lawn mower, then browse our fantastic selection today.

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