Introduction: Creating a Knife From a Lawnmower Blade

The shop I work at  recently got a whole bunch of lawn mower blades so I have been trying to find things to make them into. One of the things that occurred to me was if lawn mower blades are strong enough to hit a rock then they might be a good candidate to make knives.

In addition to the instructions on making the knife I will include an explanation on how I replicate the knife design. (I ended up making 4 of the same ones)

These steps are not exhaustive and assume the maker has experience with some basic metal working tools.


Tools used

-Plasma Cutter
-Angle Grinder (with different grit flap disks)
-Bench Grinder
-Die Grinder


Materials

-Knife Template
-Lawn Mower Blade
-Sharpie

Step 1: Safety

Remember when working with power tools to use the proper safety equipment.

In this case it would include:
Safety Glasses
Respirator  (remember grinding disks are putting many nasty things in the air)
Earplugs

Optional
Gloves (although not necessary and not for use when working at a forge I like to use a good pair of leather gloves to lessen the vibrations when I am working with grinders.)

Step 2: Making/Tracing the Pattern

If you do not have a knife already created that you wanted to replicate then you need to design a knife outline.

To get an idea of what kind of designs work I would suggest first cutting different patterns out of cardboard and seeing how they fit in your hand. Then when you have prototype you like then you can transfer this by simply laying your template on the lawnmower blade and moving it until it fits. Now just trace your template with a sharpie and you are set to cut it.

Step 3: Cutting the Pattern

Now that you have the outline of the knife the next step is to cut it out.

I did this with a plasma cutter but there are other options for cutting it.....(Oxy Torch, Metal Saws)

 This is where the process become more difficult. If you are not completely comfortable with the plasma cutter it is better to run some practice cuts on the ends of the material to get a feel for how the thick lawn mower blade cuts. When you are ready cut out the blade along the lines as smoothly as possible.

Remember the better your cut is the less grinding you have to do later!

In the final photo you can see how rough my cut was compared to the finished blade. (I should have practiced the next one I did was much smoother) The rest of the steps will be refining this blade to its final shape.

Step 4: Refining

So now we have the rough cut blade and need to refine it to its final shape. Its also during this step that we will grind the blade to clean steel.

To refine the blade place the template back on top of the blade and darken the areas that still need to be cut. Now you have an idea of what still needs to be ground away. To grind back the edges I prefer the bench grinder, it cuts fast and removes material on edge accurately.

This does not require a lot of precision but make sure not to cut too far!


Now using the angle grinder and either a flap disk or debris/paint removal disk get rid of the junk and paint to expose the bare metal. At this point the knife should look very close to the template. Remove any more material to get the exact shape desired. If nessary trace the outline off of the template again.

Now on to cutting an edge...

Step 5: Cutting an Edge

Now that the shaping is finished an edge needs to be ground onto the knife. The best way to do this is a combination of angle and bench grinder.

At this point the goal is a light touch. If to much pressure is applied or the angle is wrong the edge can quickly become ruined. Take your time and line up the angle and run the grinder along the length of the blade slowly and lightly taking extra care where the blade comes to a point..

If you have not done this kind of grinding before it would be a good plan to practice on scrap first. It will save trouble down the road.

Put the final edge on using a fine sanding disk. At the same time run around the edges of the blade to put a smoother edge on the areas you were grinding to shape.

The last step is finishing the surface of the blade.

Step 6: Finishing the Blade and Final Thoughts

The finishing process can be achieved in many ways. I chose a rough finish for my knives with a melted beeswax coating. I could have worked my way through slowly increasing grits and polishing compounds to achieve a mirror finish but I was not interested in that look.

This blade was not forged or tempered. It is durable but will not hold an edge as well as a tempered knife.

I constructed this knife at Combat Ready Arts in Kalamazoo MI

Comments

author
Schmidty16 (author)2013-04-27

very creative

author
Schmidty16 (author)2013-04-27

very creative

author
jbrauer (author)2013-04-26

This is a really cool design, but a shame it isn't heat treated. Here is how you can do it with a propane torch and a kitchen thermometer:
1) Heat the metal red-orange hot, until a magnet won't stick to it.
2) Quench it in some oil (including corn/canola) that is at about 280F.
3) Polish it to bright metal so you can see the colors.
4) Heat the spine (not the edge) of the blade with the torch.
5) As you heat, watch for the cutting edge to heat up to a straw-yellow, almost purple color. The spine should be a darker blue.
6) When you get to straw yellow, quench it in oil again.
7) Polish and sharpen.

There are other ways to accomplish this, but this is a basic DIY that I've tried and works.

author
sonicdrive (author)2013-04-24

a easy trick to get a good harden steal edge is to weld it with some chromium steel rods on the edge and temper it once you have the shape you want a solid bead will last a long time just my 2 cents

author
rimar2000 (author)2013-04-23

All lawn mower blades I know are mild steel, in order to diminish the risk of it breaks. Hence, the edge never will be a well sharp one. I reinforced the edge of mine with hard steel to avoid sharpening it so frequently.

author

I have been doing some research into lawn mower blades and it seems that they are made of tons of different kinds of steel. I ran across this forum where no one could decide what the majority of lawnmower blades are made of. I am going to put a nice edge on mine and see how it holds up, that should help me figure out what kind of steel I am working with.

author

Forum I was talking about URL: http://www.bladeforums.com/forums/showthread.php/657675-lawn-mower-blade-steel

author

Well, while I was writing my comment I thought that possibility. I can't say I know the matter, I have seen only some blades, but all of them was mild steel. They lose the sharp edge very easily.

author
ZaneEricB (author)2013-04-23

Very nice! I had to reharden my blade i made out of garden shears. I did it in a BBQ pit after grilling some steaks...quenched it in some cooking oil, so it would have that carboned finish.
I like what you have done here....

author
Gregbot (author)2013-04-23

EXCELLENT! THANKS! (yes! I had to shout that!)

author
mdaniel5 (author)2013-04-23

Lawn mower blades are never a tempered steel, because of risk of fracture caused by accidental rock that may hit it. If you want some good knife steel you want to use old lumber bandsaw blades, they are durable, but will also hold an edge much better than a lawn mower blade.

author
HeWhoMakesStuff (author)mdaniel52013-04-23

I have heard about those band saw blades working well. I just need to get my hands on some....

I did try tempering one of the blades I made a discovered that the lawn mower steel tempers much harder than mild steel.

author
Kiteman (author)2013-04-23

That's a nice "fantasy" shape, but it doesn't look comfortable to hold - maybe wrap the handle end in strips of leather?

author
HeWhoMakesStuff (author)Kiteman2013-04-23

Its actually surprisingly comfortable, but I am designing a handle and sheath for it. Probably made of wood and leather.

author
Kiteman (author)HeWhoMakesStuff2013-04-23

Cool - next instructable?

author
HeWhoMakesStuff (author)Kiteman2013-04-23

yep probably in a week or so

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Bio: I am a maker of objects with a background in art, theater and design. I work in many materials but my most common are, metal ... More »
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