Choosing the right angle grinder disc for sharpening your lawn mower blades is crucial for achieving a clean, sharp edge. With so many options on the market, it can be tricky to determine which disc will work best. This article will examine the key factors to consider when selecting an angle grinder disc for sharpening blades and provide recommendations on the best discs to use.
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Angle Grinder Disc Types
Angle grinder discs come in a variety of materials, grit sizes, shapes and thicknesses. Here are the main types of discs used for sharpening lawn mower blades:
- Aluminum oxide grinding discs – These abrasive discs are common for sharpening. They come in various grit sizes with coarse grits being more aggressive for removing material and fine grits better for polishing.
- Zirconia alumina discs – More durable than aluminum oxide, these discs have excellent cutting ability and last longer.
- Diamond discs – Contain industrial grade diamond for the most aggressive grinding. Diamond is extremely hard and cuts very fast.
- Flap discs – Abrasive flaps on the edge of the disc conform to curves and sharpen difficult to reach spots.
- Unitized wheels – Composed of layered grit material bonded together. Provides consistent grinding across the disc surface.
- Cup stones – The abrasive is mounted on the edge of a cup-shaped disc. Allows sharpening inside curves and crevices.
For sharpening a typical lawn mower blade, aluminum oxide and zirconia alumina discs in the 36 to 60 grit range are recommended. Coarse grits cut aggressively to reshape and sharpen the edge quickly. Finer 80-120 grit discs can then be used for honing and polishing the edge. Flap discs and cup stones also work well for sharpening the curve of the blade.
Disc Size
Angle grinder discs come in sizes from 4 inches up to 9 inches in diameter. For sharpening lawn mower blades, 4 1/2-inch and 5-inch discs are ideal. The small size allows sharpening the curve of the blade and accessing tight areas around the mounting bolts. Larger discs may work for the main straight cutting edge but cannot sharpen the entire blade.
Safety Considerations
Use caution when sharpening with angle grinder discs. The grinding process generates sparks and dust. Wear safety goggles to protect your eyes and a face shield if you have one. Use hearing protection as the noise levels are high. Wear cotton or leather gloves to protect your hands. Work outdoors or in a well-ventilated area to disperse dust and particles. Let the tool do the work rather than forcing it to avoid potential kickback from the disc. Keep the guard on the grinder and adjust it to block sparks from hitting your hands or body.
How to Sharpen Lawn Mower Blades
Follow these steps to sharpen your lawn mower blades with an angle grinder:
- Remove the blade from the mower -Disconnect spark plug wire, drain gas and use a block of wood to prevent the blade from turning as you loosen the mounting bolt.
- Inspect and clean the blade – Look for cracks or excessive wear and wire brush off any built up debris.
- Clamp the blade securely in a vise with the cutting edge facing up.
- Attach the grinding disc to the angle grinder. An aluminum oxide 36-60 grit disc is a good choice.
- Position the grinder so the disc is on the cutting edge with the edge angled up slightly. This will recreate the original bevel angle as you sharpen.
- Turn on the grinder and slowly move the disc from side to side across the edge. Apply light pressure and let the disc do the work.
- Continue sharpening until you have an even, uniform edge. Remove any nicks, gouges and indentations.
- Use a finer grit 80-120 disc to refine the edge.
- Turn blade over and repeat the process on the opposite cutting edge.
- Balance the blade and reinstall on the mower, checking for clearance.
Taking your time with each step will result in a razor-sharp edge. Remember to keep the original bevel angle. Test the edge for sharpness and examine for any high spots or uneven grinding. A nicely sharpened blade will glide through grass and provide a clean, even cut.
Best Angle Grinder Discs for Sharpening
Based on performance, durability, safety and value, here are my top picks for the best angle grinder discs to use for sharpening lawn mower blades:
| Disc | Details |
|---|---|
| Norton Rapid Prep Abrasive Disc | Aluminum oxide disc that cuts fast and smooth. Stays cool while grinding. Durable anti-loading design. Good value for the performance. Multiple grits available. |
| 3M Cubitron II Flap Disc | Lasts up to 10X longer than standard discs. Conforms to complex blade curves. Cooler grinding reduces risk of altering metal properties. Highly versatile for sharpening. |
| Weiler Unitized Wheel | Engineered grit layers prevent loading for consistent grinding. Cuts faster and cleaner than other discs. Leaves a satin finish edge. Great for initial shaping and sharpening. |
| Diamond Tech Dia-Sharp Cup Stone | Industrial grade diamonds cut the hardest steels with ease. Ideal for sharpening straight edges or inside curves. Wet or dry use. Multiple grits available. |
I recommend starting with a lower cost but high performance option like the Norton Rapid Prep to reshape and sharpen the majority of the edge. Then use a finer grit Rapid Prep or Weiler unitized wheel to hone the edge to sharpness. For the curve of the blade, the 3M flap disc will follow the contour well. The Dia-Sharp cup stone can also be used dry on the inside curve where a disc can’t reach.
Tips for Sharpening Lawn Mower Blades
Here are some additional tips to help sharpen your mower blades like a pro:
- Check that the blade mounting holes are round without wear to ensure proper bolt torque when reinstalling.
- Balance the blade after sharpening to prevent vibration and uneven cutting. Special balancer tools make this easy.
- Match the original blade bevel angle – often 25-35° for mower blades. Use a protractor to check.
- Work slowly and methodically. Causing excess heat can change the blade temper.
- Grind until the edge burr forms, then flip to remove it. This will leave a very sharp edge.
- Consider removing the blade for sharpening if possible. It’s much easier than grinding on the mower.
- Invest in a bench grinder with a grinding jig for easy sharpening without a vise.
- Angle grinders with advanced vibration control allow you to better feel the grinding process.
When to Sharpen Lawn Mower Blades
Here are signs it’s time to sharpen your mower blades:
- The lawn appears frayed after mowing instead of a clean cut.
- Blades seem to lightly skim over the tops of grass rather than cutting.
- Your mower is leaving uncut patches in the lawn.
- Engine bogging down easily when mowing.
- Excess vibration from the mower.
- Blades show nicks, dings or deformation from hitting objects.
As a general rule, sharpen mower blades at least once per year. But it’s best to inspect blades periodically and sharpen when dullness is noticed. Dull blades make mowing harder on your engine and uneven cutting will leave your lawn looking bad. Keeping blades freshly sharpened will have your mower working like new again.
Conclusion
Choosing the best angle grinder disc for sharpening lawn mower blades boils down to selecting abrasive discs in the right grit, size and shape to effectively grind and hone the cutting edges. Aluminum oxide and zirconia alumina discs in the 36-120 grit range offer a balance of cutting speed, life span and finish quality. Smaller 4 1⁄2 or 5-inch discs allow sharpening the curve of the blade. Premium discs from brands like Norton, 3M and Weiler provide excellent cutting performance and durability for a reasonable cost. Follow basic sharpening steps and safety precautions, and you can restore your mower blades to like-new condition.