Why Sharpen Your Mower Blade?

A dull blade tears grass rather than cutting it cleanly, leaving ragged brown tips. Torn grass is more susceptible to disease and drought stress. A sharp blade cuts cleanly, the lawn recovers faster and looks better. Sharpen at the start of each mowing season or every 20–25 hours of use.

Safety First

Always disconnect the spark plug lead before working under a mowerThe blade can spin if the engine fires accidentally while you work. Remove the lead from the spark plug and tuck it away from the plug before tilting the mower or touching the blade. Wear heavy gloves when handling the blade — even a dull blade can cut.

Step-by-Step

  1. 1

    Disconnect the spark plug lead and drain or stabilise fuel

    Remove the lead from the spark plug. If the tank has fuel, either drain it or keep the carburettor side up when tilting (prevents fuel leaking into the air filter).

  2. 2

    Tilt the mower and remove the blade

    Tilt the mower so you can access the underside. Block the blade with a piece of timber to stop it rotating while you loosen the central bolt. Use the correct spanner size (usually 15–19mm). The bolt is typically reverse-threaded — turn clockwise (right) to loosen. Remove the bolt and blade carefully.

  3. 3

    Clamp the blade in a vice

    Secure the blade in a vice for safe sharpening. Do not attempt to sharpen a blade by hand without securing it first.

  4. 4

    Sharpen at the existing angle (30–45 degrees)

    Use a metal file or an angle grinder (faster). Match the existing bevel angle — typically 30–45 degrees. File in one direction (away from you, into the edge) using long smooth strokes. The goal is a sharp edge, not a razor edge — a razor-thin edge chips quickly. 10–15 passes per side is usually sufficient. Remove equal metal from both cutting ends to maintain balance.

  5. 5

    Balance the blade before refitting

    A blade that is heavier on one end causes vibration that damages the mower engine. Balance by hanging the blade through its centre hole on a nail in the wall or a dedicated blade balancer. If one end drops, that end is heavier — remove a little more metal from that end and retest until it hangs level.

  6. 6

    Refit and reconnect

    Refit the blade with the cutting edges pointing the correct direction (usually cutting edge faces the direction of rotation). Tighten the bolt firmly — it must not come loose during operation. Reconnect the spark plug lead.

When to replace rather than sharpenReplace the blade if it has large nicks, cracks, severe bends, or is worn very thin. A damaged blade can break during use and become a serious projectile hazard. Replacement blades cost $15–40 and are worth the money for safety.

Frequently Asked Questions

Look at cut grass after mowing — brown or torn tips rather than clean cuts indicate a dull blade. Also check the blade directly: run a fingernail carefully across the edge (carefully). A sharp edge catches slightly; a dull edge feels rounded and smooth. Significant nicks or divots visible to the eye mean the blade needs sharpening or replacement regardless of age.
You can use a drill-mounted sharpening attachment designed for in-place blade sharpening. Results are less precise than bench sharpening and you cannot balance the blade in place. For occasional home use it is acceptable, but for best results remove the blade and sharpen properly on a bench.