Introduction: Make a Lawn Mower Blade Knife

Picture of Make a Lawn Mower Blade Knife

Make a sweet knife out of a old junk lawn mower blade .

Step 1: Things You Might Need

Picture of Things You Might Need

Tape measure , square and or straight edge, pencil and marker, grinder , cutoff wheel, flap wheel, grinding wheel, and a couple of different sanding discs for starting the polishing finishing process, clamps for holding the material , A bucket of water would be helpful to for keeping the material cool. And one good lawn mower blade. For more detailed work a dremel tool may be handy.

Step 2: Make a Design

Picture of Make a Design

In this step you can use a piece of cardboard or paper for a pattern if you would Like. I just freehanded my knife. Use your imagination here. A blade is a blade you can make it as simple or as fancy as you desire. I draw them in pencil first so I can make corrections and then trace over with marker.

Step 3: Cut Your Part Out

Picture of Cut Your Part Out

Clamp your part so it does not move. Use your cutoff wheel to make the basic shape and take your time so you do not build up too much heat. Use your bucket of water to splash the part occasionally to cool it down . You do not have to take all the material off at this time, use your grinding wheel to make your finishing shape.

Step 4: Make Corrections to Your Shape If Needed

Picture of Make Corrections to Your Shape If Needed

Hold your knife and change your design as needed . Make sure it is comfortable to hold and use. Use your flap wheel to help finish your design it will take off less material and be easier to use.

Step 5: Make a Edge

Picture of Make a Edge

Take your grinding wheel and cut your Edge . Take your time to not build up heat because the sharper it gets the thiner the material will be and the hotter it will get.

Step 6: The Finish of Your Knife

Picture of The Finish of Your Knife

At this point you can finish it how you would like, I used my sanding disc to clean smooth and polish my knife . I then used polishing compound and a buffer to get a shine. You could also sandblast and paint your knife .

Step 7: Sharpen and Enjoy Your Knife

Picture of Sharpen and Enjoy Your Knife

Resharpen your knife with a stone or other sharpening devise . At this point you're done enjoy.


1flipflop (author)2014-10-03

Watch movie King Arthur. A scene shows a decapitation with a very large sword if true imagine how sharp for such a large thick blade must have been. Point is to me doesn't matter the quality of steel just the sharpness and what you will be cutting I have had a lawn business so my job is to cut things YES or NO???????

Drachengraff (author)1flipflop2014-10-04

Actually broadswords, bastard swords, and the two-handed style blades had a edge so dull you could run your hand down it and it wouldn't leave a cut. It was the size and weight of the weapon that produced to cutting action. There is a great documentary on the Viking Ulfbert sword. They had a demonstration with a katana and then a broadsword. The demonstrator actually did run his hand down the broadsword blade and leave very neatly chopped a tatami mat in two just as he did with the katana. I recommend this video to anyone interested in swords and ancient weapons.

Nickynui (author)Drachengraff2015-09-21

that isn't entirely true, they did HAVE a sharpened edge, it just wasn't razor sharp, but they were sharpened every day after the knight trained (they were made from inferior iron). whereas Katana's were made from what we know as Damascus Steel, it was extremely hard. and they had a concave blade. (so basicly there were to microscopic blades)

Drachengraff (author)Nickynui2015-09-22

I have to respectfully disagree. I have seen demos by European weapon masters. There was a great one at the Tower of London, and another in Cologne, Germany. The swords (broadswords) had edges but not anything you could cut yourself with by running your hand down the blade. The cutting power was from the force of the blow and the angles of the cuts. I have no idea where you heard that broadswords were made from inferior iron. But that is patently false. Iron swords were older, from a different time. True, Japan, China, and the Middle East had access to better steel earlier than European countries, but we are talking about the early Dark Ages. Later periods caught up with the expansion of trade. Think the First Crusades. Though even then, swords were of good steel. Just not great steel. So was the armor for that matter. Later swords were made of higher quality steel. Some were even made with damascene or pattern welded steel. During Renaissance times the swords in Europe were every bit as advanced as Japanese Katana, as this was around the time period the Katana came to the pinnacle of it's art. But they were not broadswords! Compare a broadsword to a late Italian long sword or a cutlass and you'd be surpirsed.

Starfist (author)Drachengraff2014-10-11

A blunt sword is completely useless! Theres no cutting Power on a dull edge, no matter jow big or heavy your sword is!!!

youngblade (author)Starfist2015-01-15

That depends on what you define as dull. Different tools have different relative scales of sharpness. A knife's edge isn't gonna be the same as a sword or an axe.

OdinsTech (author)Drachengraff2014-10-11

I've see this documentary and approve this message.

amirho24 (author)2015-03-12

its very goooooood . i wnat to make it now . thx

lkay5 (author)2015-02-02

GREAT instructable! I didn't have to fill in the gaps with my imagination! you walked me through it perfectly! now, I'm off to buy a new blade for my mower so I can make a small axe and a knife with the old one. RECYCLING HAS NEVER BEEN THIS MUCH FUN!

tazavier1 (author)2014-12-14

I honestly would love to try this I will content how this would go after trying it in the summer.

BrockGrimes (author)2014-10-13

Popular mechanics used to publish articles on how to temper or harden blades. Basically you hear it then drop t in used motor oil. It'll add carbon and harden the edge. You can use the same method to harden a wood drill bit to drill steel. Google it.
But here's one on blades:

jaxboy (author)2014-10-07

I have some small gardening tools I had custom forged in Korea from car springs several years ago that work excellently, and have never needed resharpening. They quickly developed a thin layer of rust, but it seemed to protect the tool from further rust. I just went to look at the tools, and discovered that they had been put away with dirt on them 2 years ago. After scraping the dirt off, they looked like they did a month after I got them. By the way, all the hand scythes the rice and wheat harvesters use are made by the same forgers using the same springs. They are very inexpensive, too. I think in the mid 1980s, they were about $1.75 each.

folderman88 (author)2014-10-07

A lawnmower blade is a poor choice for making a knife when you spend your time doing the same thing with a better steel that will hold a sharp edge.

diy_bloke (author)2014-10-03

With the discussion on steel quality going on I cant help recalling a National Geographic documentary (or was it Discovery) on Japanese swordmaking in which the making of a traditional sword was compared with an american sword maker making it.
The Japanese craftsman had to preorder steel that was only mined in small quantaties once every two years. I think he basically got it as a raw block of iron and he spend a loooooong time hammering it, molding it, folding it etc etc. then went to a process of covering parts of the blade with clay in the hardening and tempering process, then finally had a high quality sword made according to age old tradition.
the american sword maker, just ordered a band of high quality steel, went to work with an angel grinder and a laser cutter (or a plasma cutter) to get to the raw shape. Then started forging it, using liquid nitrogen in the hardening and tempering process.
In the end he had a high quality sword made by modern methods.

So... which one was better. ofcourse they were tested and compared... they were basically equal in quality albeit that with one test the Japanese sword chipped off a piece of the cutting edge..... but the modern made sword was a hell of a lot cheaper and faster to make :-)

With regard to the tempering/hardening of the lawnmower blade, I just do not know the quality of the steel, but I guess that even if it would be a softer blade, you'd still be able to skin a cat with it. ('skin a cat' meaning 'getting the job done')

pfred2 (author)diy_bloke2014-10-04

Are you sure you're remembering that documentary right? Because the real samurai sword making masters do not order their steel, they smelt it themselves in a ritual ceremony. Perhaps they order some metal stock for supplying the tourist trade though? Got to pay the bills too after all.

diy_bloke (author)pfred22014-10-06

i can only state what was in the documntary. His 'order' was on an amount of ore that was dug up once every two years. It isnt that he ordered a plate of ready made steel. just the ore. If he then processed that himself I do not recall

pfred2 (author)diy_bloke2014-10-04

If there is one thing that I have learned over the course of my life it is that not all steel is equal. Neither is the quality of the job that they can do for that matter. With the best of blades you could skin a whole herd of cats.

Mo0k (author)2014-10-05

Hello Zombie, hello Halloween.

gravityisweak (author)2014-10-01

What type of metal are lawnmower blades made from?

pfred2 (author)gravityisweak2014-10-01

Lawnmower blades are made out of mild steel. Lawnmower blades are soft so if you hit something hard they do not shatter, and break. A lawnmower blade that shatters, and breaks could be potentially pretty hazardous if it happens while the lawnmower blade is spinning.

I hit a chunk of concrete mowing some tall grass in my backyard once, the blade bent like a hook. So I took it off the tractor and hammered it back straight again. Yehaw! I should add that I took that chunk of concrete and tossed it into the woods a bit. I don't want to hit it anymore when I mow.

1flipflop (author)pfred22014-10-04

By the way so in case you don't know you can always copy and paste to edit a comment, since there is no edit option ...s0oO I hit a piece of mild steel with my mild steel blades and that mild steel was lodged into deck with such force I opted to remove medium carbon steel bolt that held the (redundant) mild steel blade in place, the force was so great It stripped the threads that were (in my opinion) in the high carbon spindle and went to local mower shop that instant for part to get (large church) job done

agdobias (author)gravityisweak2014-10-02

While the blades are made out of mild steel, there's a fair amount of carbon in them...though not as much as a spring (totally different process). The type of blades that the author presented will keep a nice edge (provided you're not trying to cut an anvil!), and provided you don't make the blade too long, it shouldn't bend.

I made one out of an old file file once, and while I could keep the edge razor sharp, it proved to be too brittle.

Dark Solar (author)agdobias2014-10-02

Apologies, sir, but I cannot allow this statement to pass unchallenged; mild steel, by definition, is steel containing .3% carbon or less and cannot be hardened via quenching. Mower blades are, in point of fact, hot-forged from mildly corrosion-resistant 10XX steel in the 40-50 range and left unhardened specifically to retain the quality of toughness while still allowing for retention of a cutting-edge.

pfred2 (author)Dark Solar2014-10-02

If there is so much carbon in lawnmower blades then how come they spark like mild steel does? All I ever get out of lawnmower blades are showers of yellow straw sparks. I work with steel on a regular basis and I don't see lawnmower blades being any different than mild structural steel as far as composition goes. Lawnmower blades are soft, they do not even hold an edge particularly well just cutting grass. By rights I should sharpen my blades about every third cut. But I usually don't get on it that much.

1flipflop (author)pfred22014-10-04

Who sharpens your blades? What mower is you have? 3 cuts is all you get ? is not much, do you use it on a very sandy environment ? Is your area to mow five acres each cut ? I have a lawn business on commercial equipment the cut is 36 inch with 2 18inch blades the sharpened edge part of my blade is about 8 inches long, that has 2 edges per blade so 4 times 8 = 32 inches of cutting edge not 3 time 2 inches like on non commercial use blade, I also have a 21 inch cut Toro commercial Pro mower its blade also has about 8 inches of cutting edge surface to it I would sharpen my blades myself after a complete day of mowing and usually kept extra set of sharp blades along just incase I went the extra mile even had extra set of junk blades to do those unsightly lawns or sandy or junk lawns that didn't require a premium cut my junk blades were from sets that I would sharpen numerous times till the blade edge was at a certain minimum and also since I did frequent sharpening I could keep my edge part of blade straight they never got angled say smaller width or tapered down especially at the tip was very hard to keep very tip end keen or squared on the very end of blade itself is not to get rounded it should stay square at tip of edge part as a commercial grinder I own makes it easier to upkeep sharpens because your not MOWING a lawn unless your blades are sharp. Keep your blades sharp and true and they will take. care of you

Note steel with a carbon content above 2.14% is considered cast iron

note found at link below bottom of chapter 1

agdobias (author)Dark Solar2014-10-02

No apology needed. I appreciate the clarification and will soon be stockpiling mower blades to build swords for my Goblin Army. :)

Dark Solar (author)gravityisweak2014-10-02

Mower blades are typically made of a mildly corrosion-resistant 10XX steel in the 40-50 range. Excellent for heavy choppers, swords (if you stack a billet), hunting/utility knives, and chisels. Kitchen knives or engravers' tools...not so much.

pfred2 (author)Dark Solar2014-10-02

Mildly corrosion resistant you say? Real mild judging by the rust I'm seeing in this picture

gravityisweak (author)Dark Solar2014-10-02

Lots of info, thanks. I think if I made something out of a lawnmower blade it would end up being more of a decorative piece than a working piece, but who knows. Anyway, most of this is over my head, but what does it mean to stack a billet?

Dark Solar (author)gravityisweak2014-10-02

It's just smith-speak for "take a pile of smaller pieces and forge-weld them into a larger chunk". :D

bobwojo (author)2014-10-03

Many commercial mowers use MARBAINĀ® lawn mower blades, might be a good choice for this project of you have access to them.

SnoogleH (author)2014-10-03

Nice job rg2013.

I see several comments on hardening/tempering mower blades. "Yes", you can harden and temper a knife or other tool made from a lawn mower blade. The steel varies in quality from manufacturer to manufacturer and is engineered more for "Toughness" than holding a razor edge. However, they do contain enough carbon to make a functional cutting/digging/chopping tool. I find them to be a bit thick for some knives but are a good choice for large ones like "Bowie" knives.

diy_bloke (author)2014-10-03

I got to try this once. btw, I have exactly that same straight angle and stanlyy measurement lint. I think for at least 30 years already :-)

ZaneEricB (author)2014-09-30

Just a suggestion....lawnmower blades tend to be more malleable than you may like in a knife or axe.... what do you think about tempering the blade?

pfred2 (author)ZaneEricB2014-10-01

I don't think there is enough alloying elements in the steel they make lawnmower blades out of to really harden them much. If you did the process right you might get some case hardening to happen on a lawnmower blade I suppose. But I don't think that would do you much good as you sharpen the edge. You'd abrade the case hardening right off. What you might be able to do is run a bead of hard face weld onto the blade edge. Then you'd have a bit of hard(ish) metal to work with.

No matter what you do I don't think you're ever going to be able to turn a lawnmower blade into A2, or 440C, or any other recognized steel for blade making. Maybe if you folded it and hammer forged it Damascus style with some good alloy steel? Nah, seems kind of crazy to me.

People do that with steel cable though, and it comes out pretty cool. Then the carbon can get up inside all of the individual strands before you hammer weld it all together. So maybe that is what you'd have to do? Draw the lawnmower blade into wire, then forge bundles of it? Yeah, I can see that working.

The sad fact is there is more to quality steel than a simple heat treatment. A lot more.

Carmelite (author)pfred22014-10-02

Actually, the composition of lawnmower blades is most likely a high carbon steel. Now it probably isn't a highly engineered blade steel or anything, but it probably isn't bad.

Now, given that it's a high carbon steel, a proper heat treat will go a long way to making the blade harder. As for rust resistance, heat treatments don't do much to help that. It's worth noting that back before well established steel grades, knives and useful cutting implements were simply "carbon steel" due to the charcoal and coal used in forging. And they worked well enough.

pfred2 (author)Carmelite2014-10-02

Actually I've ground enough lawnmower blades to know it isn't high carbon. Heck you can sharpen lawnmower blades with a file. Lawnmower blades are mild steel.

ZaneEricB (author)pfred22014-10-02

"The sad fact is there is more to quality steel than a simple heat treatment. A lot more."

Very true....but... it couldnt hurt ;-)

a.steidl (author)2014-10-02

Nice ible. I haven't got any lawnmower blades, but I do have some steel that may be suitable for a similar project. Need tools though. Anywho, I like the idea. A piece of constructive criticism: Your knife may rust quickly without some protection from skin oils, moisture in the air, etc. It may be a good idea to put oil or beeswax on the steel to protect the surface from oxidation.

jshelton8 (author)2014-10-02

I have some knives my grandfather made from lawnmower blades

Mario2007 (author)2014-10-01

won't all the grinding leave the blade brittle without tempering again?

tomatoskins (author)2014-09-30

I've never thought to use a lawn mower blade. I've use truck leaf springs before. Nice instructable!

About This Instructable




More by rg2013:Make A Lawn mower Blade Knife
Add instructable to: