If the blades of grass appear frayed after mowing, the blades are blunt. High time to grind the lawnmower blade. With a little manual skill, you can do this work yourself. The following instructions explain step-by-step how to do it.
Safety is the key – this preparation is what counts
Occupational safety is the top priority when you sharpen a lawnmower blade yourself. It must be ensured that the mower cannot startup. You should exercise this caution in all work related to the maintenance of a lawnmower.
Here’s how to do it:
- Disconnect the spark plug connector on the petrol mower
- With the electric lawn mower, pull the cable out of the power plug
- Remove the battery from a cordless mower
In addition, robust work gloves and protective clothing are mandatory. Ideally, wear long-sleeved clothing, long trousers, sturdy shoes, and safety goggles.
material and tool requirements
If all the work materials and tools are within reach, the lawnmower blades can be sharpened quickly. This is how you should be equipped:
- Open-end wrench or adjustable wrench
- Allen key
- pipe wrench
- File in workshop quality
- whetstone, e.g. B. Scythe whetstone
- rubber mallet
- Lawnmower Owner’s Manual
How to remove the lawnmower blade
Turn the mower over to access the mower blade. Position a petrol mower so that the air filter is at the highest point. This way, on most models, no petrol will leak out of the tank. Now refer to the lawn mower’s operating instructions and then remove the cutter bar.
If the operating instructions have been lost, this does not prevent you from continuing your work. Use the ring or open-end wrench to loosen the center retaining screw. Memorize the position of any washers well.
A lawnmower blade of a petrol lawnmower should never be sharpened while installed. The risk of flying sparks igniting spilled petrol is far too great. It is safer to remove the cutter bar to grind it some distance away from the mower.
Manual sharpening tops the grinding machine
The removed lawnmower blade is fixed in a vice, which simplifies all subsequent work steps. Proceed with these steps:
- Use the file to grind the lawnmower 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 sharpening a lawnmower blade with a flex. The knife is heated excessively, which results in a coarse grinding pattern. In addition, the removal increases unnecessarily, which can cause greater imbalance. This is only corrected by a corresponding material removal 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 blade should be resharpened immediately.
Unfortunately, this is at the expense of a relatively large amount of material on the blade.
As long as the quality of cut on the grass is acceptable, the lawnmower blade will be progressively worked from the correct side with each subsequent grind. In this way, the correct edge angle gradually moves to the desired side. Here the angle should be set a little flatter as long as both sides of the knife are still sharp.
If the bevel on the wrong side has disappeared due to wear, increase the angle again on the right side.
Protecting the lawnmower blade from an imbalance
If you do not grind a lawnmower blade to the same extent on both sides, the cutter bar will later flap back and forth more or less uncontrollably due to an imbalance in the mower. You can prevent this situation as follows:
- Drive a nail horizontally into a piece of sturdy wood
- Use this to hang up the cutter bar by its central hole
- If one side tilts down, there is an imbalance
- Sand the heavier side on the lawnmower blade again
Ideally, you should use this method to check the balance on the lawnmower blade 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 leads to an extensive lawnmower repair.
How often should lawn mower blades 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 blunt them more quickly.
As a rule, one grinding per season is sufficient to mow a lawn perfectly. If you take a regular look at the lawnmower blade, you don’t have to worry about frayed grass.