Let's Talk Sharpening Lawn Mower Blades

We've discussed sharpening chainsaw chains recently and you guys gave me some great insights. How about mower blades? I've always just thown them in a vise and wailed on them with a grinder until there was kind of an axe edge, albeit with a bevel only on the top side. This cuts better than the round blade that it was, but never as well as I'd like. We have thick bahaia grass that is a beast to cut, I've always got sprigs sticking up that got missed.

Any expert tips or tricks for sharpening a lawnmower blade? Is there a magic angle? Bench grinder, angle grinder, file, sharpening stone? 

I use a bench grinder.  chisel edge with the bevel on top like you said.

https://youtu.be/1baxssnbMMw

Expensive!

I've never understood why people take a motorized grinder to them.  I always use a file.

Grind at the existing angle. go slow, stopping often, and letting it cool until you can hold your hand on it. If you see colors in the metal, you are removing the temper. Lawnmower blades are tool steel. Cooling it in oil can't hurt. I like to finish with a file.

I sharpen mine with a file, but make sure to hang it on a nail every once in a while to check balance.  Years ago, I sharpened one and took off too much on one end and it almost shook the mower to death.

-Rob

I will dress mine with a file, but sometimes it has taken one two many ugly sticks at 3400 rpm to be fixed with elbow grease.  That's when I fire up the bench grinder.  As with any blade, a shallow angle will be sharper, but lose its edge faster.  Just try to copy the factory bevel.

I like the nail balance method, but I take it a step further.  The friction between the blade and the nail can sometimes be an issue, so I have a nail with an old clutch throwout bushing on it.  The blade can roll the bushing on the nail easily without having to physically move on the nail and can be more accurate.  No need to be perfect, but get it as close as you can for the health of the crank and bearings.

Since I moved here, my neighbor has a sharpening business and he'll do it for $6 so I have kinda quit doing it myself.  Nice to support a mom n pop business and have a beer with a neighbor.  He has a piece of rebar on his bench with a funnel on top of it upside down.  The rebar is ground to a point like a pencil so the funnel balances. Kinda like the old analog tire balancers.  He sets the blade on the funnel on the rebar and eyeballs the blade with the surface of the bench for level.

Keeping a sharp blade will have big benefits that you can't really see.  A dull blade will cut grass and it will look the same as a sharp blade, but if you look closely at the cut grass, a dull blade kinda rips the grass with a jagged edge.  This leaves a lot more surface area that evaporates more water, and also it's more of a wound for the grass to heal.  Kinda like if you get a cut from a razor blade it will heal faster than if you got a cut from a chainsaw. If you mowed half of your lawn with a dull blade and half with a sharp blade, you would see a notable difference by the end of the season.

Ermagerd!  A file?  Really?

Maybe if you sharpened it after every use.  The blades I see will typically have a rounded, blunt edge with a few big chunks missing.  I always use a bench grinder, and it takes a while to remove enough metal to bring the edge back.

1988RedT2 said:

Ermagerd!  A file?  Really?

Maybe if you sharpened it after every use.  The blades I see will typically have a rounded, blunt edge with a few big chunks missing.  I always use a bench grinder, and it takes a while to remove enough metal to bring the edge back.

Samesies. I only do mine once a year, generally in the fall when I'm doing all the other maintenance. If I used a hand file to sharpen all three blades on the rider, plus the one on the push mower, I'd still be out there now!

Dremel with a grinding stone is how I do it. Takes maybe half an hour to drop the deck, flip it over, grind both blades, then put it all back together.

I use a bench grinder.  Takes me about 3 mins once every couple of years.

I don't cut my lawn, I beat the weeds into submission.

At least I did, recently sharpened the blade for the first time in the 8 years I've owned it. Eye opening difference!

Bench grinder. Mine get so destroyed so quickly that I keep a spare set to sharpen and then swap them on.  I also put a nail in the vice and make sure they aren't too light on one side. 

I have an old foley blade sharpener and balancer. I still just buy new blades if they get too screwed up.

Not like they cost enough to warrant worrying about.

Belt sander. 220 grit. Lock it in a bench vice and go to town.

Good tips. I never thought about the nail balance but that's an excellent idea. Also hadn't thought about watching the heat for temper. 

X about 10 on using a file at this point    Part of my spring PM routine on the tractor, I’ve never had any issues with balance / vibration.  Sharp blades definitely make a difference in keeping the lawn healthy and looking good.