How to sharpen your lawn mower blades

1. Make the mower safe first

For petrol mowers, remove the spark plug lead so it cannot start by accident. For cordless mowers, remove the battery. Then wait for the blade to stop fully before doing anything else.

To be fair, this is the bit people rush. Take your time here and you avoid most accidents.

2. Empty fuel or position the mower properly

If it is a petrol mower, avoid tipping in a way that can spill fuel or oil into places it should not go. Check your mower manual for the correct tilt direction.

Put the mower on a stable surface and use gloves before handling the blade.

3. Mark the blade orientation

Before removing it, mark which side faces down (for example with chalk or masking tape). It depends on the mower, but blades fitted upside down are a common cause of poor cutting afterwards.

4. Remove the blade carefully

Use the right socket or spanner size and hold the blade with a block of wood to stop it rotating. Keep washers and bolts in order so they go back exactly as they came off.

5. Clean and inspect the blade

Scrape off packed grass and check for cracks, deep nicks, bends, or heavy corrosion. If the blade is damaged, replace it rather than sharpening it.

A cracked blade is not one to gamble with.

6. Sharpen both cutting edges evenly

Use a flat file, bench grinder, or sharpening tool to follow the existing bevel angle. You are aiming to restore the edge, not make it razor sharp like a knife.

Remove similar material from both ends to keep balance sensible.

7. Check blade balance

Use a simple blade balancer or rest the centre hole on a suitable round shaft. If one side drops, take a little more metal off that heavier side and test again.

An unbalanced blade can cause vibration and strain on bearings.

8. Refit and tighten correctly

Refit the blade in the correct orientation and tighten to manufacturer guidance. Reconnect spark plug lead or battery only when everything is back in place.

9. Test cut on a small patch

Start on a small area first and check finish quality. If the cut is still rough, the blade may need further sharpening or replacement.

How often should you sharpen?

For regular domestic mowing, once or twice per season is typical. If you hit stones, roots, or twigs often, you may need to do it sooner.

When to call for help

Call Richard if the blade bolt is seized, the mower vibrates badly, or you are not sure the blade is balanced and fitted safely. Better that than risking damage to the mower or yourself.