Introduction: How to Turn a Scissor Blade Into a Folding Knife
In this tutorial I am going to be showing you how I took a scissor blade from an old pair of broken scissors and turned it into a small but functional key ring folding knife!
Firstly I ask you to watch the YouTube video as it shows each step much better than still images ever could (I tried to edit it so it is as fast paced and interesting as possible)
Also If you are interested in making a folding knife I strongly recommend that you watch my fully narrated 2 part tutorial on how to make a friction folder as it may help to explain some steps and answer any questions you may have.
With that said enjoy the tutorial!
Also if you are feeling extra kind and you did appreciate the effort that I put into this tutorial then please consider voting for me in the full spectrum laser contest!
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Step 1: Finding Your Blade
First you need to find your blade from which to make the folding knife. Forling knifes are generally made from stainless steel due to its corrosion resistant properties and so are scissor blades so that is going to be my source of steel. The blade of the scissors is almost always hardened to a certain extent (which is what you want for a good knife blade). In general the cheaper the scissors the worse the steel. Another good source for hard stainless steel is old kitchen knives and you will probably be able to get a larger blade.
For my knife I am going to use a broken pair of scissors that I found at school, if you go to any normal school there will probably be no shortage of broken stationary. Otherwise it may be time to sacrifice an old pair of blunt scissors for a good cause. The blade that I am using is small and from quite a cheap pair of scissors but it will do for the small key chain knife that I want.
The next step is to separate the blades from the scissors. This can easily be done by drilling out the rivet that holds them together. I did not need to do this step as the blades that I was using had already been broken apart.
After that the handle must be removed from the metal. For most scissors this is made from a thermo-softening plastic like HDPE or PET and one possible way of removing the blade would be to heat it with a blow torch but I didn't go down this route as it may release toxic fumes from unknown plastics or overheated plastics and it has the chance of overheating the blade and softening it (and the whole reason for using a scissor blade is that its hard already!) Instead of this I decided to use the brute force method, using a combination of hammering, crushing and cutting to remove the plastic. Once removed I can see the full shape of the steel so I can maximize the length of the blade.
Step 2: Designing the Blade and Mechanism
Now it’s time to design your
folder. I am going to be making a friction folder as it is by far the simplest style of folding knife and does not take too long to make. A more complex project for the future might be to make a frame lock design for a knife like this.
My designing process is quite crude and simply involves a pen and paper. I traced out the shape of the existing scissor blade and then decided on what to remove to make it into a knife. After that a handle shape can be made, I simply used an existing folding knife that I already had and scaled the handle down a little. The folding mechanism consists of 2 pins. The first is the pivot for the blade and that is going to go through the hole that is already in the blade from the rivet to save me having to drill any holes. The 2nd pin is the stop pin that limits the rotation of the blade to roughly 180 degrees so that it can open and close but not fold too far in any direction.
Once designed the shape of the knife is cut out and it’s time to start cutting out the blade!
Step 3: Cutting and Shaping the Blade
Now it’s time to turn that design into reality using tools!
There are literally thousands of ways to shape a knife blade ranging from a rough rock to 5 axis CNC machines. I would not recommend too many heavy abrasive tools that will heat up the blade and ruin the hardness. I used a combination of a belt sander, and angle grinder and some small files for the precise final shape of the blade. Any of these tools would have been fine for the entire shaping of the blade. To check that the folding mechanism is the correct size I hammered two nails into a piece of scrap wood to act as the pins and tested the rotation of the blade. At first it would not turn far enough so I removed some more material that contacts the pins and then tested it again until I was happy.
Then it was time to bevel the knife blade. Again there are hundreds of ways to do this both high tech and expensive to cheap and cheerful. I decided to go with the latter and made the entire bevel with a hand file. This took quite a while and I would not recommend it for a larger, thicker or harder blade and it actually made my new file a little blunt. After filling I gave the edge a little sanding to get rid of any deep scratches and smooth out the edge. I the used my homemade MDF power stropping wheel that I made in another tutorial to sharpen the blade to razor sharp.
An advantage of hand filling the edge is that it has little to no chance of overheating the steel where something like a belt sander could. I decided to use a chisel grind on this blade since that was the style of grind already on the scissor blade at the time. This also meant that the blade had a super sharp edge.
Step 4: The Handle
The handle will be made from scrap aluminium sheet that I had left over from another project, this means that the entire knife was made for free from scrap material - I it when I manage to make something for free from scrap!
The handle works kind of like an aluminium sandwich. Two thicker sheets enclose the knife blade and they have a thin spacer the same thickness as the blade at the back so that the knife is able to rotate.
The handle design was transferred onto the 3mm aluminium sheet and the pin holes were punched through onto the metal. It was then time to drill them out using a 3mm metal twist drill bit in my drill press. Then it was time to cut out the metal, I did this using a large hacksaw and then metal files to refine the shape and because the aluminium is quite soft this did not take too long. Once the first half of handle sandwich is made I copy it exactly for the other side. Once they were both exactly the same I glued them together using CA glue. This meant that any further changes would be replicated across both pieces. Using a half round metal file I rounded both sides of the handle so that it was comfortable to hold.
After rounding I used a lighter to heat up the aluminium. This breaks the glue bond between the two pieces so that once cooled they can be cleanly separated. Any excess glue can be removed using sandpaper.
The shape of the spacer material should be designed to take up any excess space in the handle that the knife does not while folded away. The spacer can then be cut out using any appropriate method. Since mine was only made from some 1.2mm scrap aluminium it was easiest to use tin snips for the rough shaping and then move onto files for final profiling. The holes of the handle were transferred to the spacer and then it could be pinned in place.
The pin that I am using is a 3mm steel nail. Something more fancy like brass can be used but I wanted to keep this build free. The pin was inserted and cut to length, roughly 1mm longer than needed. Then using the anvil on the back of my bench vice and a 32 ounce ball peen hammer I rounded over the edges of the pin, expanding it and crushing the layers of my handle together.
The handle was then sanded smooth using sandpaper ranging from 100 to 600 grit. I could have at this point buffed the metal to a mirror finish but I decided not to as the knife is going to be a keyring knife that will rub against the hard metal of my keys all day long in my pocket and the soft aluminium is bound to get really scratched up and a mirror finish will only highlight those scratches.
Once smooth it was time to insert the blade and peen over the pivot and stop pins to lock them in pace too. This is done the same way as with the previous pin. The amount of pressure on the knife from the pivot pin is very important as it directly affects the amount of force needed to open and close the knife. The more you hammer the pin the harder it is to open the knife. If you over hammer the pin you can use a blat blade screwdriver to pry open the handle gently to release pressure on the knife.
Once the pins are sanded down smooth the knife is almost complete!
Step 5: Finishing Touches
Time for some final touches.
First I used a small steel file to add some notches in the handle every 5mm to make it look a little nicer and also to give it a little more grip. I also drilled a small hole in the back of the handle and added a little snap link key ring thing so that I can attach the blade to my key ring.
Overall I am quite happy with this project! I love the idea of making something entirely for free from scrap. Realistically I am not going to use this knife very much but it is just more of a nice thing to have on my key ring. It may have a bit of use opening my many packages from amazon.
I hope that you enjoyed this project, if you did then post any questions that you have below!
If you want to see more like this then check out my YouTube channel as I rarely type up many of my videos as it takes ages!
Participated in the
Full Spectrum Laser Contest 2016
Participated in the
Before and After Contest 2016