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

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

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

Picture of 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.

Picture of 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

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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!

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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.

Picture of 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.

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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

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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

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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.

Picture of 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

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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.

Picture of 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.

Picture of 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.

Picture of 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.


awesomeal (author)2016-06-10

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.

RandyJ22 (author)awesomeal2016-06-15

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.

Seymour Heine (author)RandyJ222016-06-17

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

RandyJ22 (author)Seymour Heine2017-05-17

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

Seymour Heine (author)RandyJ222017-05-17

Oh, sweet irony.

RandyJ22 (author)Seymour Heine2017-05-19

How so?

RandyJ22 (author)2017-05-18

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

_diyMATT (author)RandyJ222017-05-18

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

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

RandyJ22 (author)_diyMATT2017-05-19

You are welcome, Matt - glad to help.

Ronny Ponny (author)2016-09-30

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.


BigAndRed (author)2016-09-20

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.

almerkel (author)2016-06-19

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.

carpetony (author)2016-06-11

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. .

RandyJ22 (author)carpetony2016-06-15

Hit ITS fair share of rocks.

carpetony (author)RandyJ222016-06-16

My fone its two smart four me.

_diyMATT (author)2016-06-16

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

ElvisM7 (author)2016-06-11

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 .

jsklein (author)2016-06-11

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

DBlaser (author)2016-06-11

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

LawrenceS18 (author)2016-06-10

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...

_diyMATT (author)LawrenceS182016-06-10

Yep. I mention I have one in the video.
Real men can torque bolts down by feel too. :)

Eh Lie Us! (author)2016-06-10

Good read. THanks for sharing. SO does this mean that I have to mow the lawn now?

CathyNoyb (author)2016-06-10

If nothing else, this Instructable had me laughing til I CRIED! Best part is, I wish I'd seen this several years ago, BEFORE I sliced open my knuckle trying to use one of those stupid handheld blade sharpeners, a mistake I won't make again. That little accident left me with a serious infection, for which I was treated with a drug that was later determined to cause severe adverse reactions in my body (I was allergic to it and could have DIED) and rusty blade fragments permanently embedded in my finger. THANK YOU, ColumbusCOOK, for brightening my day.

TexM1 (author)2016-06-09

The Video was easy-watching due to the humor and visuals on each step. Clamps are worth their weight in gold (as are ratchet straps by the bucket load!) so your tip on your clamps for price and purchase location was also very useful. Also useful are other tips that I've read below about maintaining your mower body, as well as how to reduce the "Klingons" from mowing! LOL Great job for a cook on the blade sharpening! I'd expect nothing less from someone who understands how key your blades are in the kitchen. As a combat Army veteran, I would say that not only are SHARP blades key in the kitchen and yard, but in life in general. Not only on the battlefield, but also off the battlefield when you have to shave every single day.... after all, if you're getting written up by the 1stSGT every hour for being our of uniform because of that 5 O'clock shadow, then you'd best bet, like Matt with the mower, is to CHECK THE BLADE... and make it sharp!

deswiger (author)2016-06-09

Yea, nice job. A couple of things extra I did when I was rebuilding mowers is to take a wire brush to the undercarriage after scraping to get to the metal. Fill in any rust and/or extra holes, either by welding or bondo or bubble gum (not really but something) then spay all of the undercarriage with a cooking spray (PAM or some sort). This will help in cleanup later on not allowing the cuttings to build up so much. Also as you put the blade back on, make sure it is as close to being level with the bottom of the case without going past the bottom. This help cut the grass cleaner with less bogging down.

Before I got a grinder to do this much faster, I had to tie down my drill with a grinding stone on it. Hey, whatever works, safely of course.

Good job, thanks for the info. Semper Fi

John BarryL (author)2016-06-09

To prevent grass build-up on the underside of the deck, after you get ALL the grass off, wirebrush it (don't forget to take off the plug wire), get it squeaky clean, then spray paint it with some graphite spray, like E-Z Glide (Tractor Supply has it). Just remember to spray in a well-ventilated area, perhaps even with a respirator mask. Also consider safety glasses.

Dawsie (author)2016-06-09

lol every time I find a mower at the tip,Dad gets me to bring it home so he can strip it doen for parts :-) by now the mower is nooner the original that we bought due to the parts being changed and replaced :-)

The only thing that I did have to buy for it were the springs on the mower speed end as they stretch after awhile and second hand ones never work :-/

I did like the tip of the par cord I found I was even able to add just a little more on then spinal which gives me a longer pull than I use to get so now I can get the mower started with one pull :-) but my old push mower still cuts better than all of the Petrol mowers even if it has no motor :-) just as well I love cutting my grass as I am out there with it all the time :-) only need the Petrol mower after it has been raining and I want to collect the grass clippings for the compost bin :-)

Thanks for the tips :-)

_diyMATT (author)2016-06-09

Keep all the cool tips coming. I am loving some of the stuff I am leanring.

John T MacF Mood (author)2016-06-09

I did the same clean procedure, but went a little crazy step further and used a pressure washer and detergent, and got every little bit of stuck on grass and detritus off, and used silicone spray to keep the buildup down.

I also had to replace my pull cord, so I cleaned out a lot of GRUNGE from the areas under the cover that were blocking the air intake areas. Snap, it was running better for it...

(BTW, Paracord will work well as a substitute for the "Brand Name" pull cord kit that costs you an arm and a leg. Being nylon. it slips through the guides and works maybe better than the "Brand Name" cords. Paracord is usually UV stabilized and MAY last longer.)

Amazing tips. That paracord one is killer.

John T MacF Mood (author)2016-06-09

Love the Instructable, ColumbusCOOK ! You have quite a humorous and instructive style, I enjoyed this one, and will use the info!

JosephB38 (author)2016-06-09

Funny and good info. I do this several times a season to both trim mower and rider. You can avoid the build up under the deck 1-by mowing while grass is dry 2- by spraying silicon under the deck of the mower each time you sharpen your blade. Mowing while grass is wet either from rain of heavy dew can and does cause undue wear and damage to the mower. A sharp blade helps to lessen the strain on motor and moving parts and helps to maintain a healthy lawn.

_diyMATT (author)JosephB382016-06-09

Silicone on the deck is a terrrific idea. I might go do that right now. THanks. :)

Joeyjan19 (author)2016-06-09

hammer a nail into the side of your workbench and spin the blade lightly. mark the high side and spin again, if it ends with the same side up grind a little off the low side to balance the blade. also I suggest not using wd-40 Anti seize compound does a much better job available at the local auto parts store. It is worth keeping around for anything you want to eventually take apart, in gold or silver. Gold for higher temp.thanks bye

Joeyjan19 (author)Joeyjan192016-06-09

p.s. Block the blade with of wood 2by4 works well so the blade is in the center of the 4 side against the housing. If you can't brake it loose with a large socket large or open end wrench get some Kroil oil. It comes in a spray can also at auto parts store and is the best for breaking loose rusted bolts.remember if you break the bolt you have really compounded your situation,watch those fingers.bye

_diyMATT (author)Joeyjan192016-06-09

The silly thing is I have anti-seize in my garage someplace. Just never occurred to me for some dumb reason.
Ah well. :)

sheripres (author)2016-06-09

You are too funny! I love the write up! FYI - I do remember the 70's and I remember cutting the grass barefoot as a child!

I should get a T-shirt that reads "I survived Lawn Jarts, no seat belts, no helmet, and mowing the grass barefoot in the 70's and all I got was this lousy T-shirt".

_diyMATT (author)sheripres2016-06-09

Preach on. The 70's when seatbelts were jammed into the crack of the seat. Good times.

rburke712 (author)_diyMATT2016-06-09

Ha-off the topic of sharp blades but...standing up in the back seat of my father's 1964 Convair, as he drove down the NJ Turnpike!

I survived to age 54. Darwin would be happy.

PS: Sharpened my blade a few weeks ago. Just used my Dremel with a grinding tip. Forgot to unplug, the plug, and luckily my 10 fingers are still attached. (See above)

sheripres (author)rburke7122016-06-09

YIKES, Rburke712! I only drive manual vehicles and I never thought of the blade "jump starting" the mower. I will definitely remember this conversation about the plug!

Oh the thrill of jumping in the back seat in those very solidly built cars! Today - kids are strapped in tight and DVDs are played while they drool all the way across the country on their family vacation! ha

Obviously, not ALL families are like this, but I have seen them on the turnpike.

grdbrg (author)2016-06-09

I pull the plug wire, turn the mower on its side with the carburetor up and grind with my 4" angle grinder. About one minute if the grinder is nearby. Just got a cordless grinder.

Once a year I might pull off the blade, sharpen, balance and change the oil.


RockeyDA (author)2016-06-09

go juce on air filter? my mower has no choke so to start it i splash alittle gas in the combustion chamber and put a bit in the air filter,1 pull starts for me! i also have a dumpster dive mower thats hard to start, i usu alot of adapters and a socket set on my drill.

RockeyDA (author)RockeyDA2016-06-09 best way to start mower

Knight Lamune (author)2016-06-09

A few oddball mowers do use a left hand thread on the bolt. This is especially true with dual-blade decks, since they usually spin opposite each other.

Figure out what direction the blade spins then turn your bolt the other way!

_diyMATT (author)Knight Lamune2016-06-09

Smart tip.

Kinnishian (author)2016-06-09

Great instructable! But, need that obligatory comment : WD-40 is not a lube! You should use it neither for the good times, nor the lawnmower times. General purpose lithium or silicone grease, or some lube meant for staying put, would be better I think.

dpruett (author)Kinnishian2016-06-09

WD-40 is a solvent with light lubricating properties. If you mow a lot and remove/sharpen your blade often, spraying the bolts with WD-40 will work just fine. If you only take your blade off once a season or less, I'd use anti-seize paste or extreme pressure grease - otherwise a very light coating of motor oil with your finger tips works great (which is what I usually do, since I've always got motor oil handy). I probably wouldn't use general purpose grease, just because it's messy and I'd be worried about the bolts vibrating loose over time.

_diyMATT (author)Kinnishian2016-06-09

Totally agree. I just ran with what I had though. I'd rather go with some WD than run the chance of having a dry hole. :)

threeoutside (author)2016-06-09

Thanks for this video! As a widow on my own, I need all the info I can get on how to take care of the lawn tools. And I like your style :)

exgi93 (author)2016-06-09

You can avoid heavy build-up of clippings in future by using a mulching blade which is designed to really pulverize them, i.e., there's not so much left to stick to the underside of the deck. It's particularly important to keep a mulching-type blade good and sharp, too.

About This Instructable




Bio: Alton Brown taught me how to cook, now I want to tackle diy projects.
More by _diyMATT:I Made a #battlecar Out of My Soccer Mom Minivan.Homemade Cat ScratcherA Fidget Spinner Made Out of Fingers Aka a Finger Spinner
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