Sharpening the end of a lawnmower blade?

ToddS

ToddS

Joined
Jan 15, 2015
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446
I came across the idea a while ago that the end of rotating blade should cut (or slice) much more efficiently than the side. Just like a string trimmer cuts most efficiently with the tip of the string. The person suggesting this seemed to imply that lawnmower blades should be sharpened at the ends, not the sides (as they normally are). Essentially the end draw-cuts while the side push-cuts and obviously the draw cut is much more efficient.

My question is whether anybody has seen or heard of blades sharpened this way? I've been waiting for the grass to start growing to experiment with this myself.
 
When you buy a set of blades, the areas that are supposed to be sharpened are already sharpened. No need to reinvent the wheel on it, R&D lab engineers are paid lots of money to figure out what cuts best. Also, if you were to attempt to regrind the blades, you might throw things out of tolerance and at best decrease efficiency... and at worst injure yourself or others.

Personally, I’d stick to just touching up the designated areas. I use one of those rough circular stone drillbits that come in a kit with a plastic balance. I think they’re like $20.
 
3fifty7 said:
Id expect dramatically reduced blade life if you do.

Also, why ?
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The article I am referring to was written by Tony Atkins who literally "wrote the book" on cutting, and is an expert on rotary slicers, like deli slicers. In particular, he explains why slice-cuts are so much more effective than push-cuts.

The quote is:

Rotary lawnmowers cut quite well with badly damaged blades owing to the high rotational speed giving high (slice-push ratio); it is the tangential edge, rather than the radial edge, of the blade that does most of the cutting.
 
Perhaps the design of a mower blade has as much or more to do with flinging air and grass up and out the exhaust port as it does with actually cutting grass? For the outer edge to do most of the cutting it will need to have a sweep, and that swept edge might negatively affect flow, e.g. if it relies on tip vortices?

If the blade rotates at 2500 rpm and the mower moves forward at 2 mph that's 0.85" per rotation or 0.425" per tip, so there would need to be that much sweep to the edge to keep the cutting on the end rather than the face of the blade.
 
Professional Landscaper here.
A mower blade does more than just cut. A well designed blade creates suction and lifts up the blades of grass while cutting it.
On a blade for example thats 21 inches long, the most used section of blade is about 6-7 inches on each end. That takes the most wear. The closer to center edge takes the least. Sharpening the outer end of the blade will give no benefits. There’s no really contact with that section and the mowers cutting path.

The reason a string trimmer cuts at the tip is the angle at which it’s used. If you lay a string trimmer perpendicular to the ground and run it across the grass it cuts horrible. Secondly a string trimmer cut in a whipping motion.
 
My curiosity piqued by the question posed, I found this video explaining the importance of the 'vacuum' effect in making lawnmower blades work. I agree, for it to work this way, the aerodynamics inside the blade's rotating radius are what make it work. The 'lift' of air, which makes the blades of grass stand upright to be cut, is created by the upturned trailing edge of the blade. I'd think the same uplifting suction-effect might not exist at the outer ends of the blade, which might render sharpening the blade at the end essentially moot.

 
fatBatman said:
When you buy a set of blades, the areas that are supposed to be sharpened are already sharpened. No need to reinvent the wheel on it, R&D lab engineers are paid lots of money to figure out what cuts best. Also, if you were to attempt to regrind the blades, you might throw things out of tolerance and at best decrease efficiency... and at worst injure yourself or others.

Personally, I’d stick to just touching up the designated areas. I use one of those rough circular stone drillbits that come in a kit with a plastic balance. I think they’re like $20.
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You forgot the lawyers who are the final word of the design, which is never good for how well the design functions for it's intended purpose. Like keep those mower blades butter soft so if you hit a rock, or anything else you shouldn't be running over, it won't fracture. God forbid the cutting edge was hardened at all!

Hey, I'm in. I am always curious to see if something can be improved. Not sure how to measure the difference in blade changes though? I have an electric mower and just got 2 new blades for it this spring. I am open to modifying one if need be. I have been curious about a swept forward cutting tip to grab the grass as it cuts into it. Think positive rake on a cutting tool.
 
Diemaker said:
You forgot the lawyers who are the final word of the design, which is never good for how well the design functions for it's intended purpose. Like keep those mower blades butter soft so if you hit a rock, or anything else you shouldn't be running over, it won't fracture. God forbid the cutting edge was hardened at all!

Hey, I'm in. I am always curious to see if something can be improved. Not sure how to measure the difference in blade changes though? I have an electric mower and just got 2 new blades for it this spring. I am open to modifying one if need be. I have been curious about a swept forward cutting tip to grab the grass as it cuts into it. Think positive rake on a cutting tool.
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My thought was to compare a new blade to an old blade with the standard radial edge ground off and a 15 degree tanto-like edge ground into the end. Also, i don't see any reason not to sharpen both the radial and tangential edges.

I guess it would be easy to compare the cleanness of the cut edges on the standing grass, but it might be worth measuring the current draw from an electric mower.
 
I inherited a lawn mower from my blind grandfather. It was soon very evident he had been cutting the lawn with the blade on backwards. It still cut.
 
eveled said:
I inherited a lawn mower from my blind grandfather. It was soon very evident he had been cutting the lawn with the blade on backwards. It still cut.
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I think the lawn was the least of his (and everyone else's) worries!
 
I should have said he was legally blind. He could see a little. Enough to mow the lawn. More or less.

I could not beat him in bowling unless I lied about what pins were still up. But if I pushed it too far he’d catch me and say. I’m not that blind. Lol.
 
On behalf of scythe users everywhere, thank you for demonstrating its superiority. :cool:

(One of the best tools I've ever purchased or employed.)
 
That was never the intended use for a string trimmer, and a scythe could not easily trim around swingset legs.

still a neat video, scythes are amazingly effective.

I have two new old stock scythe blades that have never even been handled. I’d like to play with them someday.
 
Blues said:
On behalf of scythe users everywhere, thank you for demonstrating its superiority. :cool:

(One of the best tools I've ever purchased or employed.)
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While I do love my scythe it will certainly put a spotlight on any back problems I may be having.

And if cutting thick grass putting a saw blade on the string trimmer will certainly up its game. Mine is a Honda 35cc 4 stroke with lots of torque.
 
Diemaker said:
While I do love my scythe it will certainly put a spotlight on any back problems I may be having.

And if cutting thick grass putting a saw blade on the string trimmer will certainly up its game. Mine is a Honda 35cc 4 stroke with lots of torque.
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I used to use one of these for clearing the raspberry canes that grew behind my cottage:

https://www.stihlusa.com/products/trimmers-and-brushcutters/trimmer-heads-and-blades/brushknife/

The end of the blade is sharpened at about 45 degrees from the motion to give it the mechanical advantage of a slice cut. It's funny that I forgot all about this until you mentioned it.
 
Diemaker said:
While I do love my scythe it will certainly put a spotlight on any back problems I may be having.

And if cutting thick grass putting a saw blade on the string trimmer will certainly up its game. Mine is a Honda 35cc 4 stroke with lots of torque.
Click to expand...

Showoff! :p

(I hear ya. If I've got a twinge, I'll definitely be aware of it while mowing with the scythe.)
 
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