Did you just buy a lawnmower blade, feel the edge, and thought it was dull? I recently was wondering this myself. Why are new lawnmower blades dull I thought? So I did some digging and here’s what I found out.
No, new lawnmower blades are not dull. They are sharp but not to the point that they would cut your finger on the edge. A super sharp edge would just bend over in the first 5 minutes of mowing. Plus sharp blades are more open to damage from rocks and roots. Instead, new blades are sold with a solid edge ready to work. They cut slower and last longer.
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Are They Actually Dull Or Do They Come Sharpened?
No, new blades aren’t dull. They’ve been precisely sharpened to the manufacturer’s specs.
The seemingly dull edge is done on purpose. It’s sharp enough to last for 25 hours of mowing (about 25 weeks of mowing an hour each weekend).
It’s dull enough that it won’t get damaged as easily by roots and rocks. Hitting a rock with a hyper-sharp blade will just bend the edge making it less effective. Ultimately super sharp blades die faster.
Why Lawn Mower Blades Are Like Blendtec Blades
Have you ever felt the edge of the blade in a Blendtec blender? I have. It’s dull. Or so it seems.
Why is that? Because they use a 2 hp engine that spins at 200 miles per hour. At this speed, it can break fruits and veggies down to individual cells.
If a Blendtec blade was sharp it’d simply get dull or possibly damaged while spinning. Then you’d have to replace the entire container as it comes fused with the blade.
The same thing is true for lawnmowers. Most push mowers are 2-7 horsepower. Many are just like the Blendtec blender. Just like the Blendtec that puts the tip of the blade at about 200-250 miles per hour.
Do Brand New Lawn Mower Blades Need Sharpening?
No, new lawnmower blades should be used as-is. We actually did a full analysis on what’s more cost-effective – replacing a new blade or sharpening the old one. You can read that article here to see the in-depth results.
The winner though – sharpening. Even at different assumed hourly rates for your time it was almost always better to sharpen the blade.
Both require you to take the blade off so you don’t save much time buying a new blade.
Better to sharpen it every 25 hours than replace it after 400 hours of use. That could be 10 years down the line.
Will Sharpening A New Blade Hurt It?
Yes, if the edge is too fine it could be nicked or damaged by rocks and roots. This will require additional sharpening. Each time you sharpen you whittle away the metal lowering the life of the blade.
If you buy and install a new blade just use it as is then sharpen it after a minimum of 25 hours of mowing. Check it before sharpening. If it seems to be mowing well and there are no nicks or damages, keep mowing even beyond the 25 hours.
The longer you wait between sharpening the longer the blade will last.
Can I Use The New Lawn Mower Blade Even If It Seems Dull?
Yes, just attach the new blade and start mowing. You should be able to go for 25 hours before you need to check it for nicks and scratches. Then check and sharpen as needed.
Remember, new blades aren’t dull. They are perfectly edged to maximize the time they can cut before needing sharpening.
Will A Dull New Mower Blade Kill Grass?
No, new blades are not dull. They are perfectly sharpened and ready to cut for the first 25-50 hours before sharpening is needed.
Even an old nicked dull blade that’s been running for 50 hours won’t kill your grass.
Instead of cleanly cutting grass tips a dull blade will leave the tips jagged. Plus dull blades might miss seed heads if they’re popping up. These can leave lots of tall stout seed stalks scattered throughout the yard.
When that happens just follow the videos below, spend about 1-2 hours sharpening your blade, and get back to mowing. The next time you mow those seed heads will be gone.
Is It Worth The Time To Sharpen A New Blade?
No, sharpening a new blade is not worth the time. It’s already perfectly edged and ready to cut.
Do not sharpen a new blade. You could damage it which would require more sharpening and even more of your time.
When Will a New Blade Need to Be Sharpened?
New blades need to be sharpened after at least a few hours of mowing. Typically after 25 hours, you should check the blade for nicks or damage then sharpen it as needed.
Tools Needed To Sharpen A Lawn Mower Blade
These are the tool you need to sharpen a lawnmower blade with hand tools:
- Eye protection
- Gloves
- 10 Inch File
- Vice grips to hold the blade while you file
If you plan to use power tools you’ll need a power grinder instead of a file and you won’t need the vice grip as you’ll be holding the blade and running it over the grinder.
How To Sharpen A Lawn Mower Blade With Power Tools
- Put on eye protection and gloves.
- Remove the blade from the lawnmower.
- Clean it to remove dirt and grass. You may need a metal brush to do this.
- If rusty, soak in white vinegar for 2-3 hours, use a metal scrub pad to remove rust.
- Turn on the angle grinder.
- Sharpen the 3-4 inch outer working edges.
- Use a 45-degree angle
- Sharpen till it’s butter knife sharp. Don’t over sharpen.
- Check the blade balance. Balance the center of the blade on your finger. If one side is heavier and sinking lower then sharpen that end more to lighten it up. Do this slowly and repeat till the blade balances evenly on your finger.
- Replace the blade on the mower.
How To Sharpen A Lawn Mower Blade With Hand Tools
- Put on eye protection and gloves.
- Remove the lawnmower blade from the crankshaft.
- Clean the blade of dirt and grass
- You can remove rust by soaking the blade in white vinegar for a few hours then scrubbing off the rust with a metal scrub pad
- Secure the blade with a table vice grip
- Use 40-50 strokes to sharpen the working edge at a 45-degree angle.
- Start at the top of the cutting edge and push the file down.
- Always push down. Don’t run the file back and forth.
- Feel the file teeth grab it and scrape away metal. If you don’t feel this push harder. If it still doesn’t work you may need a new 10-inch file.
- You only need to sharpen the 3-4 inch working edge at the tip of the blade. Do not over sharpen. It should cut like a butter knife. Too sharp and you’ll damage the blade when you use it.
- Repeat for the other edge.
- Check the blade balance. Balance the center of the blade on your finger. If one side is heavier and sinking lower then sharpen that end more to lighten it up. Do this slowly and repeat till the blade balances evenly on your finger.
- Replace the blade on the mower.
Hi, I’m John Stephens, chief editor and writer for Totalgardener.com. I’ve been gardening and raising animals for over 15 years starting with a small backyard plot in Northern Virginia where I grew corn, potatoes, squash, and using a high mulch technique called the Ruth Stout Method. I also raised ducks and small mammals for meat and eggs in a movable pen similar to the ones used by Joel Salatin. I later moved to Colorado where I experimented with growing greens using aquaponics inside. I eventually added a microgreens setup and home sprouting operation. I’m excited to share everything I’ve learned plus more from the other local gardening and animal raising experts I know.
