Sharpen lawnmower blades yourself - explained step-by-step

Sharpen lawnmower blades yourself - explained step-by-step

Safety is the key - this preparation is what counts

Occupational safety is a top priority when you sharpen a lawnmower knife yourself. It must be ensured that the mower cannot start up. You should exercise this caution in all work relating to the maintenance of a lawnmower. How to do it:

  • Pull out the spark plug connector on the petrol-powered mower
  • On the electric lawn mower, pull the cable out of the power plug
  • Remove the battery from a cordless mower

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Robust work gloves and protective clothing are also mandatory. Ideally, wear long-sleeved clothing, long trousers, sturdy shoes and protective glasses.

Material and tool requirements

If all work materials and tools are ready to hand, the lawnmower blades can be sharpened quickly by hand. This is how you should be equipped:

  • Open-end wrench or adjustable wrench
  • Allen key
  • Pipe wrench
  • Workshop quality file
  • Grindstone, e.g. B. Scythe whetstone
  • vice
  • Rubber mallet
  • Operating instructions for the lawn mower

How to remove the lawnmower blade

Turn the mower over so you can access the lawn mower blade. Position a petrol mower so that the air filter is at its highest point. In this way, most models will not leak gas from the tank. Now take the operating instructions for the lawn mower to hand in order to then remove the cutter bar.

If the operating instructions are lost, this is not a reason for continuing work. Use the combination wrench or open-end wrench to loosen the retaining screw in the center. Make a good note of the location of any washers.


A lawnmower blade on a petrol lawnmower should never be sharpened while it is installed. The risk of flying sparks igniting spilled gasoline is far too great. It is safer to remove the cutter bar so that it can be sharpened at a distance from the mower.

Manual sharpening tops the grinding machine - this is how it works

The removed lawnmower blade is fixed in a vice, which simplifies all of the following work steps. Proceed in these steps:

  • Use the file to grind the lawn mower blade from the outside in
  • In the second stage, rework the knife edge with the whetstone
  • Completely remove the remaining burr so that it does not fold over later and the knife becomes blunt again

Experts do not recommend sanding a lawnmower blade with a flex. The knife is heated excessively, which results in a rough finish. In addition, the removal increases unnecessarily, which can cause a greater imbalance. This is only corrected by a corresponding material acceptance on the other side.

What to do if you sanded from the wrong side?

In the heat of the moment, inexperienced hobby gardeners sometimes grind a lawnmower blade from the wrong side. If the quality of the lawn suffers as a result, the knife should be sharpened immediately. Unfortunately this is done at the expense of a relatively large amount of material on the blade.

As long as the quality of the cut on the grass is acceptable, the lawnmower blade is machined from the right side step by step with every further sanding. In this way the correct cutting edge angle gradually moves to the desired side. Here, the angle should first be set a little flatter, as long as both knife sides are still sharp. If the bevel on the wrong side has disappeared due to wear, increase the angle on the right side again.

Protecting the lawnmower blade from unbalance - how it works

If you do not sharpen a lawnmower blade to the same extent on both sides, the cutter bar will later swing back and forth more or less uncontrollably due to an imbalance in the mower. You can prevent this by:

  • Drive a nail horizontally into a sturdy piece of wood
  • Hang the cutter bar on its central hole
  • If one side tilts down, there is an imbalance
  • Sand the heavier side of the lawn mower blade again

Ideally, you should use this method to check the balance on the lawnmower blade in between and at the end of the grinding work. Only when the cutter bar is perfectly balanced is it reinstalled in the mower. Otherwise, the engine block could be damaged and a simple sanding process results in an extensive lawnmower repair.

How often do lawnmower blades need to be sharpened?

The level of use largely determines how often a lawnmower blade needs to be sharpened. If the knives often hit branches and stones, they dull faster. As a rule, a single sanding per season is enough to mow a lawn perfectly. If you take a look at the lawnmower blade regularly, you don't have to worry about frayed grass.

Tips & Tricks

In order to grow a perfect English lawn, a cylinder mower is essential. Unfortunately, its construction resists any attempt to sharpen the knives manually. Special grinding machines for cylinder mowers, however, cost more than 2,000 euros, so that such an investment will pay off in the 2nd or 3rd generation of gardeners at the earliest.