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.
-Angle Grinder (with different grit flap disks)
-Lawn Mower Blade
Step 1: Safety
Remember when working with power tools to use the proper safety equipment.
In this case it would include:
Respirator (remember grinding disks are putting many nasty things in the air)
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