Knife From a Car's Leaf Spring





Introduction: Knife From a Car's Leaf Spring

This is my first instructable so I hope that it makes sense. I will show the basic steps for making a knife from a leaf spring off a truck. Every knife will be different so I will just explain the basic steps and alternative ways of making it if you don't have the same tools that I do.

Step 1: Materials Needed

Band saw ( or hack saw )
Leaf spring
Belt sander
Sand paper
Drill press ( or hand drill )
Forge ( or home made forge )
1/4"x4"x 12" wood. Mine was oak.

Step 2: Design Your Knife

Draw out on a piece of paper what you want your knife to look like. Draw it to scale in the size you want your knife to be. Take into consideration the diameter and length of the steel you have to work with

Step 3: Heat Up Your Steel and Flatten It

Most spring steels from a vehicle will have an arc to it so
You need to heat it up and use a large hammer to pound it flat. This will also require a smooth flat surface.
Also , if you don't have a forge you can make one by digging a pit and lining it with fire bricks and just use a leaf blower with some ducting attached to it leading into the pit. Fill the pit with charcoal and your off to the races. You can also use an oxy acetylene torch. And I even have a friend who used a really hot Bon fire , however the heating is hard to control and keep even that way.

Step 4: Cut Out Your Design

Cut out the paper template you have drawn and tape it to you're steel. Then trace it onto the steel and cut it out with your band saw or hack saw

Step 5: Grind Your Edge

Use your belt sander and files to make your bevel and grind your edge. The more gradual the taper of the steel and the sharper angle you can get, the better you're knife will cut.

Side note .... I cleaned up the entire knife to make it shiny and pretty at this stage which proved pointless because I needed to re heat it later and you will too.

Step 6: Drill Your Holes

The previous picture shows the holes already drilled , it doesn't really matter when you drill them but they will just need to be drilled before you harden your knife.

Step 7: Heat Treat Your Blade

Here is some quick metallurgy for you. Hope this makes sense. When you originally heated your blade to take the bend out of it , it most likely wasent a super even heat , I know mine wasn't , and you let it gradually cool back to natural temperature over time. This will make the knife soft and it will bend if put under stress. Now what you need to do is evenly heat the entire blade until it reaches a cherry red color , not bright , but a medium to dark red. Another way to know it is the correct temperature is to bring it to non magnetic . This is known by taking a magnet and sticking it to the hot metal. When it reaches the propper temperature , it will no longer stick. When it has reached non magnetic you are going to dunk the entire blade in a container of oil or water. This is known as quenching. I'm sorry I don't have pictures of this process. It all happens really fast and you need to pay attention. I uses olive oil and dunked it in a disposable baking tray. You can use water but oil will give you a more flexible blade. Lots of people say to just use old motor oil but I read a lot of forums about horror stories due to impurities in it so I stayed away .

Step 8: Pretty Knife Ruined

This is why it's pointless to make your knife beautiful before you quench it lol

Step 9: Temper Your Blade

Now that you have quenched your blade you are going to want to temper it. Basically now that you dunked it. It has reached a hardened state. But the molecules are under tension from the rapid shock of the quench , so you take your blade and put it in the oven set to about 450-500• for an hour or so. Then turn off the oven and let the blade cool down gradually as the oven does . Some people do that two or three times. I only did it once and haven't had any problems. This causes the molecules to relax and the knife to be more flexible and less proned to snapping.

Side note .... One of my first blades I made , I heated way to hot ...quenched in water and didn't temper it. I threw it at a stump once and it exploded into 7 pieces. So those steps are important.

Step 10: Make a Handle

Trace your handle out and cut it out with your band saw or hacksaw

Step 11: Drill Your Handle Holes

Attach one side of the handle to the knife , then drill through the steel holes and through the wood. Then remove it , and repeat the step for the handle slab on the other side.

Step 12: Complete Your Handles

Attach your handles to the knife and sand them down until it's a comfortable grip in your hand. Then remove them and add either a few coats of oil or what I did which is just a clear coat exterior varathane.

Step 13: Attach Your Handles and Your Done!!

I'm sorry but I can't for the life of me remember what these bolts are called that I attached the handle with. They in screw in the middle and one side has a male thread and the other side a female and one end has a slot headed bit for tightening . I'm sure there are lots of different styles but that is what I used.

Anyways that is the completed project . I hope you found this informative . I also made a leather sheathe for this knife and I will do an instructable soon on how to make those.




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74 Discussions

Thanks again for the comments and feedback everyone. As far as how the spring steel is holding up as a blade material. So far it's been amazing. I have beaten the crap out of it. Baton'd he blade , thrown it. And it retains an edge very well and hasn't fractured or bent at all.

Hey, I'm in Mexico doing volunteer work, so I'm broke but I love making knives with scrap. This was well done, man. Did you kinda guess at the steel color? I don't have a laser heat temperature thing, and I'm still learning. I'm building a mini forge, so I'll be burning and wrecking lots of stuff learning colors.

Is there a chart online that gives some guidance on that biz?

Thanks man

Alternatively you can turn your forge blower off and temper it in there as it cools if you don't want to potentially do bad things to your oven

Hey Bushman! Nice walkthrough, I found it very informative and useful! Just one question, how's the edge of your knife hold up against other knives?

2 replies

Hey man, I have actually been very impressed with how the edge has been holding up, I gave it a non magnetic quench so it is on the lower end of quench temperatures. That makes It easy to sharpen when it gets a little dull.

Ah, I see...I've heard the harder it is to work with, the better the end result!

Can you show us a picture of the screws. I didn't understand your description. Would riveting work ok too?

How is the leaf spring steel as a blade material? Have heard mixed things about it. Would love to try it out as I have alot of leaf springs kickin around

3 replies

I have been told that leaf springs commonly used up through the mid 60's were a simple high carbon steel and work well for knives. Leaf springs after that were commonly complex alloy steels and presented mixed results when heat treating?

Just make sure not to over heat the steel. No matter how high the carbon content, if you get the material too hot, you burn the carbon out of the metal.

Spring steel my mentor told me is high carbon steel when makes good blade material cause it holds an edge longer

I believe the bolts are called sex bolts

great ible!leaf spring is a cool choice for a hand made knife ! if you want to temper razor more than the rest cover with mud japanese trick but actually they also use two different density of steel at once!

1 reply

The 'Japanese mud trick' is properly referred to and differential hardening, by coating the spine in clay, when you quench the blade it causes the exposed area to cool more quickly and the covered area more slowly creating two different crystalline structures. The key to this is a quick hardening steel though, leaf springs are 5160 steel, and that particular alloy is slow hardening so by the time your quenchent soaks the clay and cools the spine there is no difference in hardening. However you can simulate the clay idea by only quenching the edge, and will result in differential hardening.

You help me a lot with this instructable, im from México and its a little hard have a own forge (excuse my english) i made a knife with a old backyard scissors from Truper, i think its high carbon steel, i dont know but it was really great to make, i dont have pictures cause its on the oven right now, but its really great :)


3 years ago

I've got a couple of leaf springs I found while hunting we think they're from about 1940-50. So we're also thinking very high carbon content. Do you think they would make good knives?

Names for the fasteners you used on the handle are: Sex Bolt, Binding Posts, Chicago Screws, Interscrews, Barrel Bolts, Barrel Nut, Partition Screws, Door Closures Bolts, Furniture Screws, Panel Fasteners, Architectural Sex Bolts, Arch Series Screws, Hinge Screws, Display Fasteners, Screw Nuts, Connector Bolts, Threaded Rivets, Grommet Nuts, Post and Screw Sets, Book Screws, and Stationary Screws. I like "sex bolt".

Where can you find old leaf springs? I have a lot of project that I want to make that require those, so if anybody knows, please tell me.

1 reply

junkyards or if someone you know works on cars might have some, swap meets, craigslist. ..