Introduction: Pocketknife With Locking Blade

About: I am a teenager, building since I was 4 (and soldering since I was 7). I enjoy building things and inventing all kinds of little projects, some of which I share here!
I lost a decent multitool a while back, and this made me realize how important a sharp blade was to a lot of things. One of my favorite features of the multitool I had was that it folded up and had a locking blade- two features that saved my fingers countless times. I had been wanting to make a good blade for a while, and when I saw this Instructable to make a knife by Instructables user Phil Reilly, I felt inspired to give my idea a go.

Step 1: Stuff You Will Need

For this project, we will need just a few tools:
- Hacksaw (or band saw)
- Files
- A rotary tool (such as a Dremel, although this is optional. It will be used to reshape, but could be replaced by some files)
- hot glue gun
- Drill
- clamps and vice
- Sandpaper
For parts...
- Sheet metal: The stuff I used was 0.125 inches (That's about 3.15 millimeters) and was aluminium. I think i got the size right, but aluminium probably wasn't the best choice of metal- it is lightweight, but hard to sharpen. Stainless steel would be a better choice for the blade, and aluminum everywhere else.
- A spring: it needs to have a smaller diameter than the thickness of the aluminum (so that it can fit and move) and should be an extending spring.
- Hot glue: it will be used to make a rubbery handle later.
- Number 4 screws (and the corresponding nuts): Could be any other screw longer than the 3 layers of the sheet metal, as long as it is thin enough. However, this is what I had on hand, and it worked perfectly

Step 2: The Basic Design

I started by sketching an design and an outline for my knife. I wanted it to have a locking blade, so I began to think up some ideas that would do that. In the design I came up with, the lever is pulled and this is what disengages the blade. I made a template out of that idea and I cut out the parts for use later. You can make your own or download mine.
The parts include:
The left outside handle on the first layer of the knife
The blade, locking piece, and filler on the second layer of the knife
The right outside handle on the third layer of the knife.

    Step 3: Apply the Template and Cut Stuff Out

    Pretty much as simple as it sounds: Cut out the template, hot glue or trace it onto the metal sheet, and cut it out. I also filed down the rough edges and sanded the main pieces to get a more textured finish (for the handle we will be applying later). I also made a bevel on the blade piece, but I did not sharpen it. (This is for safety reasons.) I also did some strategic drilling after I decided the layout I wanted. I clamped all of the pieces together and drilled through. My goal was to have at least three holes to keep the filler in place, as well as holes that kept the locking piece and the blade in the right position. More on the mechanism next.

    Step 4: The Mechanism

    The mechanism is one of the most important parts of the knife. Here's how it works:
    The user begins to open up the blade. This makes the lever begin to roll up until it falls into the gap in the blade. This locks it into place, preventing it from closing onto the user's fingers. When the user is ready to close it, all they have to do is pull back the lever, pulling it out of the blade, allowing it to close.

    Check out this video for a look into the device:

    Step 5: Building the Mechanism

    In order to build this mechanism, I took a long, thin spring, removed the hooks on either end, inserted into it a pin made from a nail, and used that as the spring for my lock mechanism.

    The lock piece itself was shaped to properly hold the spring in place, and a hole to allow the spring to move was added into the filler piece. I wanted the spring to move so that there would be less tension on the spring and the connections.

    If you use the template I gave, then minor modifications will need to be made in order to accommodate the spring (I didn't do it on the template because I don't know what spring you will be using). Those minor modifications can be seen in the photos.

    Step 6: Holding It Together

    In order to hold it together, I used some screws. The screws I used in particular were some number 4 screws, which I picked out due to their length and diameter. I picked where I needed each piece, and clamped them together. This allowed me to drill all the way through. By doing this, I was able to put the screws in the knife and hold it all together. However, this meant that the bolt and head of this assembly was sticking out. As a result, I decided to counter-bore the hole by taking a drill bit the diameter of the head and drilling into the hole that I had drilled previously. I made sure not to go all the way through, as my goal was to allow the screw to sink into the hole while still holding everything together. This led to the threads sticking out further than I needed, so I cut them off with a rotary tool.

    Step 7: Adding a Handle

    When I had found the mechanism to be in the right place and the screws all tightened so that the pieces could move as needed, I decided I needed a way to keep them that way. I added a small dab of hot glue in each hole to keep the screws and nuts from rotating, and then covered it all in hot glue (more was better). When it had dried, I filed it down to a more gentle and finger accommodating shape. I used sandpaper to get it even finer, and this led to a soft, yet firm, rubbery handle.

    Step 8: Finishing Touches

    The basic knife is now done. For some finishing touches, you could polish the blade and leave it at that, or go a bit further. I later decided to add some serrations to the base of the blade, and I think that greatly improved its cutting ability. You could also add some personalizing touches in the handle of the blade- although I never did this, I think you could engrave a design into the rubbery handle with a rotary tool and then coat it with a sharpie. Then you could sand it all off, but the engraved bit would still be colored because the sandpaper couldn't get into the groove. 
    Check out this video for the complete design:

    Step 9: Tada!

    So there you have my design for a knife with a locking blade! I like the feel of it, and regret not using stainless steel (It would have made for a much better blade. However, I did manage to get it quite sharp as it is). I hope you enjoyed it, and please leave your thoughts and ideas. As always, have a nice day!