Lawnmower Blade Sharpening. AKA, I Need to Sharpen My Lawnmower Blade?





Introduction: Lawnmower Blade Sharpening. AKA, I Need to Sharpen My Lawnmower Blade?

About: Alton Brown taught me how to cook, now I want to tackle diy projects.

Soooo, I was not one of those kids who had to mow his lawn when I grew up. Lucky me right? Now that I am 40(ish) years wiser it dawned on me that this grass-chopper-thingy needs to be sharpened once in a while to do its job more effectively. Normally I cook, so digging around in my garage is a slightly new thing for me. This is not an exact "this is the best way to do it" type guide, but I think it's a good rough outline.

Watch the video if you swing that way, or keep on reading and view the pretty pictures instead. (your boss knows you aren't working, your ruse is fooling no one.)

Step 1: Still With Me? Good, Let's Get Things

Flip the mower over. Be sure to leave the air filter pointing up. If you point the filter down you stand the chance of dumping all your mower move juice into the air filter and making it no workie.

Step 2: Unplug the Plug or You Will Die, by the Plug, Due to the Plug, With the Plug. ...plug.

Unplug the sparkplug wire. Neglecting to follow this step can lead to accidental decapitation of your little man hands, (or woman hands respectfully). How can this happen you ask?

You know when your manual 1973 Volkswagon bug won't start and you have to push it and pop the clutch and it magically starts? That's called jump starting and this is what your lawnmower can do with as little as one blade turn.

Are you scratching your head about the words "clutch" or "manual" or even "1973"? Stop what you are doing and go get an adult to help.


(It's a sad truth that Millenials can't get their hands dirty. It makes their beards fall out. Do your part for society, give to the United Millenials Fund. Don't force your little angels to do work, they are not capable. Your money will go towards an ironic t-shirt that proves that you showed your support, minus the work.)

Step 3: Scrape Ya Goop

While you are under the lawn haircut machine, scrape off all the old crap under there. Odds are you have years of leftover lawn crud jammed up in there and now is your chance to get a clean start.

I started with a screwdriver and moved up to a chunk of angle iron to speed things up.

I scraped a good 3-4 pound of dead grass bodies off my old mower and in turn made it much lighter and easier to push.

Step 4: Unhand Me!

Now, loosen ye old bolt. Sometimes it's on pretty tight, but if you grab the blade with your gloved hand you should be able to muscle it off. Remember, righty-tighty, lefty-loosey.

Step 5: Mark It, or Run the Chance of Forgetting.

Mark the blade before you take it off. If you put it back on upside down you won't be mowing your lawn when you put it all back together, you will just be giving it a blow dry.

Step 6: Get Yourself Something to Grind On.

This could mean a lot of things, but stay away from "da club". I'm referring to strapping a belt sander to your workbench.

I'm using these mega cheap Tekton clamps for the strapping, but any will do of course.

My belt sander is another mega cheap item I use all the time. It's a plain old Black and Decker and it's maybe 50$. I even sharpen my kitchen knives using this.

Step 7: Now, Start Grinding

Hold the blade at a 45 degree and apply gentle pressure.

Remember, too much will bog everything down, too little will just be useless. (if I had a quarter for all the times I heard that)

Step 8: Quench As Needed

No, not you, quench your blade. If it gets too hot it will lose its temper and slap you around at night and send you to bed without dinner.

What are we talking about again?

Step 9: Ok, It's Sharper.

Make the blade sharp, but don't try to cut your moustache hairs off with this ladies. You don't need the blade so sharp you can cut cans and tomatoes with laser accuracy, you just want a nice edge. Once the big pits are gone you should be good to go. If you take off too much material the blade will go out of balance and be totally useless.

Step 10: Lube That Hole People

Squirt some WD-40 in the bolt hole before re-assembling. This will keep things from seizing up on your for future disassembly.

*edit, don't use WD40

Step 11: Now Watch the Video Backwards and Re-assemble Your Mower.

Tighten the bolt up until it is snug. Don't go too tight, but don't go too loose. Nobody likes loose hardware.

Step 12: Make Like an Air Freshener and Plug It in Plug It In.

Invariably you will forget to plug in your spark plug and stand in the front yard cranking away until your arm falls off. Plug it in now so you don't have to suffer that embarrassment like I did.

Step 13: Now, Take Your Little Toothpick Legs Outside and Mow.

Your grass heads will get cut off easy peasy, worms will be dead in one quick swoop, bugs will be turned into chum, all lickety split, due to your sharp new blade. Now go out and conquer your yard you weekend warrior!

Like my guides? You might like my videos too on YouTube.

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    65 Discussions

    As a Long Retired small engine Technician I have some help suggestions as well as some don't do's.

    1) Every new mower as an owners manual - read it- the manufacturer put it with the new mower for a reason. And while on that front, the engine manual will tell you to put gas stabilizer/extender into the gas container with the gas you just bought. This stops the buildup of bad Gas due to the ethanol in gas sucking up moisture. Failure to do so will lead to hard and harder starting till you end up with a fouled carburetor. And that will mean that many of you will throw away the mower in disgust. Take care of the equipment and it will take care of you. And yes the fouled carburetor can be either cleaned/parts replaced or completely replaced and still cheaper then buying a new mower.

    2) DO NOT MOW WET GRASS - it is hard on the mower, causes buildup under the machine, will not allow mulcher setup to work or will jam the opening into the collection bag. Also it is bad for the grass and may cause fungus to attack the wounded grass blade tips causing your lawn to get serious dead spots.

    3) Tipping the mower non carb side up will cause engine oil to go back thru the carb to the air filter and possibly to the gas tank - not only will you need a new filter but the carb will have to be cleaned and if gas is contaiminated , draining and replacing it. (got any ideas where you will put all the bad gas?) Also do not store a mower outside subject to the weather but do not put it in the house either(fire/explosion possible if gas is not drained out - shed, garage or under a tarp that keeps it dry. )

    4) I have found that trying to put a knife type edge on a blade is hard and actually will wear down quicker,. When you think you have a good edge gently remove the edge and leave a slightly square edge, it will cut as well but since that sgaure edge really has two edges it means it has a little bit more metal backing it up. And quench the blade frequently in water or quenching oil to retain the temper of the metal. And last the blade should be balanced - small nylon/plastic devices can be bought for a few bucks allowing you to balance it visually. There is a reason when you buy new tires or rotate your existing ones that they balance the tire rim combination. A mower blade is no different - don't run it unbalanced and risk having the vibrations go to the upper part of crankshaft and connecting rod for piston area. Oh one more thing visually check and make sure the blade is relatively flat from one edge to the other- it may have normal bends from the Manufacturing of it but if when you mount it one end protrudes lower then the safety of the edge of the deck, then buy a new blade and next time keep it from hitting rocks, roots, kids toyes etc..

    4) As suggested wire brush the underside of the deck after using a putty knife to take of the thick layers.A nice cup wire brush csn be bought at box stores to use on your hand drill. Wear gloves and eye protection. I personally think spraying your snow thrower with spam or other cooking or silicone sprays is a great idea, I do not think it adds any value to a mower deck except maybe a new mower with a virgin unused lower side of deck. If you want to make the mower more efficient then mow dry grass which will not clump and stick to the deck.

    5) SAFETY - Not only should the spark plug wire be removed, it must also not be in a position where it can flop down and make a touch contact - if any kind of contact is made the mower can start as you rotate the blade to get it in removal position. Also keep in mind if you spill gasoline tipping the machine and if there is a spark and gas fumes , then an explosion is possible. Last thought is DO NOT use antiseize fluids/grease on the mounting bolts or in the case of some mowers on the thread of the crankshaft. While it may make life easy when you decide 2 years from now that the blade is dull, it also increases the risk of vibrations loosening the bolt or nut. I love my ankles - do you? Mow the blade at the start of mowing season and during the year as needed depending on how much cutting you do.

    5 replies

    cheaper then buying a new mower

    protrudes lower then the safety of the edge

    Cheaper THAN, lower THAN, more THAN, less THAN.

    If I write it more THAN once, THEN maybe it will sink in.

    Do you really have nothing better to do than correct strangers on the internet?

    If one wants to be taken seriously for their creations/inventions, proper spelling, punctuation, and grammar make one appear more credible.

    Respectfully suggesting a few spelling corrections:
    ... to do ITS job more effectively.
    If it GETS too hot it will lose ITS temper ...

    2 replies

    Strange I had those in there like that. I know better.

    I shall blame autocorrect. Thank you kindly for the edit.

    You are welcome, Matt - glad to help.

    Great Instructable Matt... Thanks.

    If for some reason you have a Tight Nut and have a hard time holding onto the Blade.. ( and you don't have a Rattle Gun with a socket at hand )...

    ** With the Spark Plug removed,...You can feed a Length of 1/4" - 3/8"

    ( 6mm-10mm) Rope into the Spark Plug Hole and Poke it in when the Piston is down ... ( Make sure some rope is left out... to be able to remove the rope when finished) ....Then turn the Blade and it will Stop because the Piston will stop on the Rope before going over top dead center.

    ** Now I used this for a 2 Stroke... but with a 4 Stroke you may have to make sure the Piston is on the Compression stroke to have the Valves Closed , (Less chance of bending them.).

    ** Re Sharpening, I recently purchased a new "Flat Bastard File" 1.1/8" to 1.1/14" ... I didn't realize how Blunt my Files ones were... until I started Sharpening my old Garden tools ... Axes, Hatchets, Hoes and Mattocks etc... It is now something that takes no time at all ( well a Little )

    By using a Good Sharp Flat File ...( unless you are Steve Austin ).. You won't heat up the Mower Blade... and you get a better feel control of the job.


    Great instructable. You're a funny guy.

    I have 18V Ryobi tools so got the battery powered mower to match. From brand new had to sharpen the blade. Unplugged the battery, used the flap sander on my 18V angle grinder to give it a couple swipes on the cutting edge, no need to take the blade off. Ive got a very small lawn so get the lawn done with 1 lot of batteries and use what charge is left to do the edges with the wipper snipper.

    When I finish mowing I take the battery out and wash the mower and check the blade. It goes back in the shed clean and the batteries go on the charger ready to use.

    Just a simple tip for y'all. I clamp my hand-wood saw blade (like a Stanley Shark-Tooth) - flat edge up (it like Green-side Up - ya know - teeth down) and check it for horizontal level. Now I lay the mower blade (I just sharpened) on top - so I can see the saw blade edge in the middle of the mower blade's bolt hole (look into the hole - you will see a line across the middle dividing the hole). Let go of it - to check for balance. If it tilts - I grind more metal off of the side that tips down. Keep doing this until it balances (you'll never git perfect) over the saw blade edge. This is a cheap, fast and good balance tip. I have used this for 50+ years.

    Living in the Black Hills, my blade's hit it's fair share of rocks. Thanks for the fun read! Yeah, I guess I have to go sharpen and mow. .

    2 replies

    Relax RandyJ22. There is a be nice policy here. You are just trolling.

    Please Look at the camera when talking as if you are talking to someone who is sitting right there . other than that Good instructable , the Tip to Lube yourself with beer throughout is Excellent advice also .

    This was one of the most entertaining Instructables I have read. Thanks.

    I do something similar to what was done here, just with a Dremmel and a sharpening stone.

    You should torque it down to 60 ft.lbs. using a torque wrench, all real men own one, use don't want the blade to come off while it's running...