Introduction: Folding Quarter Knife
Do you have a lot quarters lying around? If you do, instead of using them the normal way and spend them (what fun it that?!?!), make something useful out of it! This instructable shows you how to make a folding quarter knife. This is only the second folding quarter knife that I have made and I already plan on making more. This project doesn't have many practical purposes, but it is fun to make! The original idea came from Miller Knives tutorial for making a folding coin knife. I made a few changes to the design, but the assembly is pretty much the same. Remember to be safe!
Step 1: Gather the Materials and Tools
3 quarters or any large coin
Nails (I used small nails and then cut off the extra material to make a small rivet)
Old saw blade
Canola oil (Optional but motor oil will also work, if you have it)
Bench grinder (I use a coarse wheel attachment on one side and a brass wire wheel attachment on the other)
Box cutter/Razor blade
Drill bit that is the same size as the nails that you are using
Propane torch (Optional)
PVC end cap (Optional)
Pliers (Optional, but if you use them, needle nose works best)
Sharpie or other way to mark the metal
Step 2: Glue Quarters Together
Using the superglue, glue all three quarters together. Make sure they are aligned the way you want, so make sure the faces of the quarters are all facing up. The reason for the superglue is to make sure the quarters stay aligned long enough to drill the holes the correct way. Just remember not to cheap out like I did on my first try. I didn't want to use superglue so I ended up wasting an hour and 5 dollars worth of quarters just because I didn't want to use superglue. DO NOT BE LIKE ME!!!
Step 3: Fitting the Quarters Together
Put the quarters in the vise. Make sure you have a towel or some other way to protect the quarters while in the vise or else it will mess up the quarters. Also, don't crank down on the vise too much because that will mess up the notches on the quarters. Now, drill a hole the same size as your nail in three corners. I like to drill holes in the bottom left, top left, and top right of the quarters. When you finish, make sure all the nails fit. When you know that the nails fit in the holes, you can pry the quarters off of each other. All you need to do is use a flathead screwdriver and pry it through the quarters. Since we didn't let the superglue stick for too long, it hasn't fully come together so it should be pretty easy to take off. Once they are off of each other, you can use a box cutter to take off the extra superglue that will still be stuck to some of the quarters. Once all the superglue is off, make sure the nails still fit into all the holes. Next, find the quarter in the middle of the stack. Find the center of the quarter and mark it with a sharpie. After you mark it, cut it in half with a hacksaw. Make sure you focus on the side with the two holes on one side (should be the left side if you drilled the holes correctly) because that is the only part of the quarter you need. After you cut the quarter, you can clean it up with your grinder.
Step 4: Making the Blade
Using the hacksaw, cut off a piece of the old saw to about the size of a quarter. The first time I tried making one of these blades, I didn't cut off enough of the saw so make sure you have more than what you think you need for the blade. It's always easier to get rid of material than to put it back on. Once you have cut off enough of the saw, draw the shape you want for the blade. I like using a hook shape for the blade because it leaves you with a sharp point. Make sure you keep some extra room at the side of the blade to make sure you have a finger notch to open the blade. Then, you use the grinder to get the shape you want. I usually keep a small cup of water to keep the blade cool when I am doing a lot of grinding or taking off a lot of material. Put the quarters together (with the half quarter in the middle) and then put the blade in the middle where the top right hole is on the quarters. Mark the hole with a pencil or a fine point sharpie. Drill the hole where you mark it, with the same drill bit you used for the nails. Make sure it all fits together. If the blade doesn't open, it is probably because you have some extra material at the bottom of the blade. To correct this, slowly take off material at the bottom of the blade. Once it fits, make the bevels on the knife. All I do for this is swipe the edge of the blade across my grinding wheel. Don't focus too much on one side of the blade, or else it will make the bevel uneven. Once the bevel is done, make the finger notch. There are several ways to do this. My favorite way of doing this is by using a fiberglass reinforced cutting disc on my rotary tool. If you have limited tools, you can use the edge of your file or use the hacksaw. You only want to make an indentation on the edge of the blade, big enough to fit your finger nail into. Do not cut more than halfway through the blade or else it will be too easy to snap off on accident.
Step 5: Heat Treating (Optional)
This step is optional but if you want your quarter knife to be a real knife and not just a knife shaped object, you should heat treat it. Heat treating makes your knife extremely hard but if you drop it, it will break like glass. Here is an article about the science of heat treating, https://en.wikipedia.org/wiki/Heat_treating Now that you understand how it works, grab your propane torch. Once you have it lit, move the knife back and forth through the flame. Once it gets to a bright red color, dip it into a small cup of oil. I am using a PVC end cap because this knife is so small. You usually only want a dull/cherry red color for heat treating but because this knife is so small, it will lose its heat quickly, so by the time it's in the oil, it will be closer to that dull/cherry red color. Be sure not to drop the blade, or else it will break like glass. If you want to be sure it hardened correctly, move a file across it and if it "skates" across the surface, you know it hardened correctly. Once the blade is fully cooled, use some sandpaper and LIGHTLY sand the blade. It doesn't have to be perfect, just enough to see some of the shiny surface of the knife. Now we need to temper the blade. What I did to temper the blade was use the lowest heat setting on the stove and moved the blade slowly through the flame with the needle nose pliers. You could also use the propane torch, but that might make it too hot. I tried to get a straw color, but it heated up too quickly and I got a pigeon blue/purple color instead. Make sure you use the lowest setting on your stove, or it will get too hot, too quick. Once it is to the color you want, let it cool by itself. Remember, it is still very hot. Once you are done with tempering, you can polish the knife. I chose not to because I like the blacker look.
Step 6: Riveting
The last step is to rivet the coins together. Put all the nails in the holes and line it all up the way you want. Then, use the bolt cutters and cut the extra material off of the nails. You should still have some stubs sticking out of the holes. Next, hammer the ends of the nails. This will cause a mushroom effect on the end and make it the shape of a rivet head. As you can see in the second to last picture, I messed up the riveting and the bottom nail twisted over. If this happens, try to cut the nail out with the bolt cutters. If the knife isn't opening, put the end of the knife (where the notch is) into the vise and try to open it that way. This will help loosen it up and make it easier to open. You can also spray some WD-40 into the hole to help lubricate it. You are now done with the knife! All you need to do now is sharpen the knife and you are ready to... do anything you can do with a knife the size of a quarter.