How to Sharpen Lawn Mower Blades – Step-by-Step
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A craftsman is only as good as his tools – so it pays to keep everything in top condition. Maintenance is an essential part of any gardening routine. Sharp blades matter not only on hedge trimmers and similar tools, but you should also sharpen your lawn mower blades regularly to achieve the best possible cut. It's easier than you might think: we explain what to look out for, when maintenance is due, and exactly how to go about it.
What happens if you don't sharpen your lawn mower blades?
Under normal circumstances, the rapidly rotating blade reliably cuts grass with a clean, straight edge, producing an even finish without torn or ragged grass stems. However, this changes as blades wear down over time – both through regular use and unavoidable contact with twigs and stones. They become blunt and the cutting surface uneven.
This naturally affects the quality of the cut. Edges become frayed, grass stems are partly torn rather than cut cleanly, and the overall finish becomes uneven. Not only does this look unsightly, but it also damages the grass itself. A frayed cut edge is larger, causing more moisture to be lost. As a result, the grass dries out and develops an unattractive greyish tinge. It also becomes far easier for disease to take hold, meaning your lawn can quickly look unhealthy despite regular care. You'll find many more lawn mower tips here.
When should lawn mower blades be sharpened?
By the time the cut becomes uneven, it's clear: it's time to sharpen the mower blades. But by then, it's already too late. The damage has been done, which means you'll need to mow again to rectify it – cutting the lawn shorter than intended. It's therefore far better not to let things get to that point. Check your blades regularly for signs of wear. As soon as clear signs of use appear, you should sharpen the lawn mower blades.
How often should lawn mower blades be sharpened?
As a general rule: you should remove and sharpen the blades at least once per season. The best time to do this is after winter, before you mow for the first time in spring. This will keep you on the safe side for smaller lawns at least. For a larger garden, you should also keep track of your mowing hours. After 20 to 25 hours of use, it's time to sharpen the blades again. This is the best way to prevent your lawn from being torn rather than cut cleanly.
Sharpen lawn mower blades yourself or hire a professional?
If you don't mind putting in a bit of time and effort, you can sharpen your lawn mower blades yourself. However, you should at least have a basic understanding of what you're doing. It's important that you end up with the blade properly balanced when you're finished, meaning you remove an equal amount of material from both sides. If you lack the experience, it may be a better idea to entrust the job to a professional.
If you already take your lawn mower in for regular servicing, the blades will typically be sharpened as part of that. If not, you can still use a sharpening service to have your lawn mower blades sharpened professionally. In that case, you only need to remove and refit the blade yourself. For a modest fee, scissor and knife sharpeners, tool retailers, or garden centres can help. The price varies depending on the type of mower and the work involved.
- Petrol lawn mower: £18 to £40
- Electric or cordless lawn mower: £7 to £22
How to sharpen lawn mower blades yourself – a step-by-step guide
Have you decided to sharpen your lawn mower blades yourself? Then it's important to take safety precautions. You should wear gloves whenever handling the machine and the blade. You should also guard against the mower starting accidentally. To prevent this, switch the mower off completely first. For an electric mower, unplug it from the mains; for a petrol mower, disconnect the spark plug lead; and for a cordless model, remove the battery. Then you're ready to begin.
Note: Before you start, inspect the blade for obvious damage such as cracks. Use a wire brush to remove all dirt and any rust. If damage is present, avoid sharpening the blade and replace it instead. If only the cutting edges are worn, you can proceed with sharpening. At this point, it comes down to whether you work by hand or use a machine.
Step 1: Removing the blade
Once you have put on your gloves and safety goggles, tilt the mower so that you can access the blade. When doing this with a petrol mower, make sure the air filter is facing upwards – it's best to tilt it backwards rather than onto its side. Remove the worst of the dirt from the underside of the machine as a basic clean. You can now detach the blade bar from the cutting deck – your mower's manual will explain exactly how. It is usually secured with right-hand threaded bolts, though left-hand thread is occasionally used. Simply unscrew the bolts while using a wooden wedge to stop the blade from turning. If the bolts are too tight, leave some penetrating oil to soak in overnight. You can then loosen them with light taps of a hammer on the bolt head.
Step 2: Sharpening the lawn mower blade
If you are using hand files, clamp the removed blade horizontally in a vice so that the wings face upwards. Take a coarse file and begin smoothing out any irregularities. Pay attention to the correct sharpening angle – for lawn mower blades, this is 30 degrees. Always file away from the cutting edge and try to remove the same amount of material from both sides. Once you have removed the burrs, switch to a finer file and refine the cutting edge. For an optimal finish, finish by drawing the blade across a sharpening stone.
If you own a bench grinder, you can simply clamp the blades in and sharpen them with ease – the correct angle for lawn mower blades is maintained automatically. Alternatively, you can use an angle grinder or a multi-tool with a grinding attachment. For the angle grinder method in particular, you should be an experienced DIYer. One wrong move can damage the blade during sharpening. Otherwise, the same rules apply as when sharpening by hand.
Step 3: Checking the balance
Once you have sharpened both sides to your satisfaction, it's time to check the balance. To do this, place the blade over a screwdriver or similar tool through the centre hole and allow it to balance freely. If the blade tips to one side, you need to remove more material from that side. It's best to check this regularly as you work. This is an essential step – if the blade is unbalanced, the high rotational speed can cause vibration. The blade will wobble up and down, leading to increased wear, reduced performance, and noticeable vibration from the mower. This is why you should always balance the lawn mower blade using this method.
Step 4: Refitting the blade
Once the lawn mower blade has been sharpened, you can refit it straight away. Use the bolts you removed earlier. Once everything is secure, you can reconnect the starting mechanisms you disconnected – the spark plug lead, battery, or mains plug.
Tools and equipment for sharpening lawn mower blades
To sharpen your lawn mower blade, you'll need a few tools. For the best results, it's important to secure the blade while you work – this helps prevent injury and allows for more precise filing. A vice that you can move around is ideal for this. For the actual sharpening, there are two options: by hand using various files, or with a bench grinder. A sharpening stone is also useful, as is an angle grinder if you have one.
You'll also need some tools to remove the blade in the first place. In some cases, complete kits are available that are tailored to specific mower models. For your own safety, it's also a good idea to wear gloves and safety goggles to minimise the risk of injury.
Depending on your mower, the necessary tools may include:
- a screwdriver
- an Allen key (hex key)
- a ratchet
- a pipe wrench
- a rubber mallet (sometimes)
- a wire brush (sometimes)
- penetrating oil (sometimes)
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