Sharpening versus Replacing Mower Blades: When Which Is Better

A mower blade that cuts poorly can often be sharpened back to work, but not always. The decision between sharpening and replacing depends on the blade's condition. Sharpening saves money, but a blade past its wear limit cuts poorly no matter how sharp it is.

When sharpening is the right call

A blade that is in good shape, with no bending, thinning or cracks, sharpens well. A slightly dull edge, honed to a clean bevel, restores a clean cut. Sharpen on a grinder, keeping the original bevel angle, and cool the blade so it does not overheat. Balance the blade after sharpening.

When the blade must be replaced

A blade that is bent, cracked, or thinned from years of sharpening has reached its limit. A bent blade cannot be straightened reliably; a cracked one can fail at speed. A blade that is worn thin near the bolt hole has lost the metal that gives it strength. These are replaced, not sharpened.

Watch for nicks and impact damage

Nicks from stones are ground out during sharpening, but deep nicks that leave the blade uneven need removal of so much metal that the blade weakens. If grinding out a nick leaves the blade noticeably thin, replace it. A blade that has hit a solid object should also be checked for hidden bending.

Match the replacement blade to the deck

When replacing, use the blade specified for the deck: correct length, lift angle and centre hole. A blade that fits loosely or has the wrong lift cuts poorly and strains the spindle. Follow the deck manufacturer's recommendation for the correct blade type.

Rotate blades to spread the work

Keep two sets of blades in rotation: one cutting, one being sharpened. This avoids downtime while a blade is sharpened. A sharp blade cuts cleanly, reduces tearing, and puts less load on the deck. Know when to sharpen and when to fit a new one, and the cut stays clean.

References

BROWN R T, DAVIES M K. Blade condition decisions for rotary mowers[J]. Biosystems Engineering, 2020, 198: 440-448.

Brown, R. T., and M. K. Davies. "Blade Condition Decisions for Rotary Mowers." Biosystems Engineering, vol. 198, 2020, pp. 440-448.

Brown, R. T., & Davies, M. K. (2020). Blade condition decisions for rotary mowers. Biosystems Engineering, 198, 440-448.