Ever wanted to be a spy? To casually walk into your class or office with that, "I know something you don't" look on your face. Well if you're like me and you don't have $100 to spend on those video sunglasses or the time to make that communication watch this is the project for you. For at least a year I've wanted to make a pen gun but every time I got online I just couldn't find what I was looking for. The pen was either clearly a gun, or just too complicated and expensive to make. So I started theorizing. I didn't have access to any explosives and didn't want the danger of my pen blowing up in my hand. Also the rubber bands and springs didn't have the umph I was looking for. Then I was reminded of when I did that classic self inflating balloon experiment with baking soda and vinegar and I began to wonder if this could be the answer. So I bought some baking soda and vinegar and gathered my tools, namely hot glue. When I finished, my pen gun shot about 30 feet and was able to stick lightly into some wood and looks almost like a normal pen. This instructable was made entirely from what I had at hand and shouldn't take more then half an hour.
1. a Z-grip Ballpoint Retractable Pen
2. 2 BIC Mechanical Pencils with Assorted Colorful Barrels .7mm
3. 2 needles (any kind works but at least one should be between 1 and 3 inches long.)
4. baking soda
5. vinegar (i used white vinegar and it worked well)
6. polymer clay
1. hot glue gun and hot glue
Step 1: Baking Soda Dispenser
The first thing you need to is disassemble your pen into all its separate parts and take the erasers out of your pencils. Now cut off a third of one of the erasers with your scissors the thinner you can make this piece the better as it will allow more baking soda to be stored. If you will notice these erasers fit very snugly in the front of the pens clear body and in the back clicker. we will use this fact to make our projectile and baking soda dispenser. Now take one of your needles and stab it through the center of the third of the eraser you just cut off as shown in the second picture above. Pliers come in handy for this part. Now place your eraser and needle into the back of your pen and push the needle down until it hits the very back of the clicker. Then push the eraser down until it won't go any farther, if the needle protrudes from the back the excess needs to be cut off. Take the needle and eraser out and cut off the excess needle if necessary. Next take the ink cartridge and cut off the clear bit as shown in the third picture. The piece just happens to fit into the back button quite nicely and the needle can be placed inside it. Hot glue the piece of cartridge you cut off to the needle with the eraser and it should look like the fourth picture. Then place it inside the back of the pen hot gluing it to the button. Just like that the baking soda dispenser is completed! Now you should have something that looks like the first picture. When you push the back button the eraser should push forward. To reset, just push the needle and eraser back until the back button is all the way out.
Step 2: Finish It!
We're almost done! Now all you need to do is make the projectile and a few touchups. First we need to fix a small problem with this pen. You might notice that there are two small holes in the body of the pen, fill them with hot glue so air can't escape out of them when the pen becomes pressurized. It's ok if the hot glue partially obstructs the barrel of the pen and can be even helpful as it keeps the projectile from falling into the vinegar that will be inside. Now that that's done take your second eraser and needle, stab the back of the needle into your eraser trying to center it as well as possible and making sure the needle doesn't go all the way through the eraser. It isn't necessary to put a needle in your projectile, but it just makes it that much cooler! Now don't load the projectile quite yet, but when you do it should look like the first picture.
Step 3: Load It
Now take your baking soda dispenser and reset it pushing the eraser as far back as it will go so the dispenser can hold the most baking soda. Fill the little cup created with baking soda and wipe around the edges so there's no baking soda outside the cup. This is where the clay comes in. Take your clay and make a little circle to seal the baking soda in. Thicker is a safer bet, but if you're going for stealth you can make it thin. The final product should look like the picture above. Now put the dispenser into the back of the clear pen body being careful not to push the back button as you put it in. Fill the pen with vinegar. If you see a little bubbling that's ok. Finally wedge the projectile into the front of the pen. Don't push on the needle as you might just push it through your eraser! But instead push on the eraser. Now slip on the rubber grip and you're done! The front bit of the pen acts like a safety and must be screwed off to let the pen fire. To fire your pen gun simply press the button and shake so the baking soda is distributed among the vinegar. That's it! You have made your very own spy pen.