If you read my previous article, “Damage Report“, you already know that I’ve been trying to make a homemade Nerf gun using a pneumatic screen door closer as the plunger, spring and pressure chamber. After my last attempt, I decided to open up the screen door closer and take a look at the guts of the thing.

I cut off the exhaust end of the tube and discovered that the spring is about 1.5x the length of the plunger tube. Also, the part in the other end of the tube that the metal rod slides through is a loose plastic piece held in by a rim on the inside of the tube. With this new info, I worked out a rough design for my second attempt.

I decided that I wanted to do three things differently.

1. While the DF3k still worked, it had some airflow problems. This time, flip the outer tube so that the plunger stops against the rim that used to hold the back of the tube in place. This leaves the end of the tube that connects to the barrel almost completely open.
2. Forget about the shell. Just make a working prototype by bolting all the internals to some wood and see if it works as a proof-of-concept. Worry about the shell later.
3. Keep the catch mechanism very simple, and very sturdy. Don’t leave any wiggle room and make everything out of aluminum if possible.

Here’s how that went:

I started by trimming the plunger tube and spring down substantially. I wanted the metal rod to be longer than the plunger tube by enough to allow a trigger and a handle in between the cocking handle and the catch. More on this later.

The plunger tube is about as long as a crossbow plunger tube, and the spring is about 1″ longer. Then I wrapped tape around the ends so that 1″ pvc fittings would fit snugly over the ends. I attached a coupler and reducer are for a barrel, and an endcap with a hole cut into it for the cocking handle. I also added a piece of aluminum to the plunger rod.

Then I bolted the whole thing to a 1×4.

I cut a small piece of aluminum and used epoxy and some wire to attach it to the plunger rod to give the catch something to catch on. Then I cannibalized the trigger/catch mechanism from the DF3k.

Finally, I attached a garage door handle to the front of the plank, and a handle to the back of the plunger rod. Remember the extra length on the cocking handle I mentioned? That’s there so that you can pull the trigger without the cocking handle slamming into the back of your hand. It’s still a little too close. I’ll have to make it longer on the next one.

Right now the epoxy is still setting, and I can’t cock the gun without the catch getting all gunked up with partially set JP Weld, so I haven’t properly range tested it yet. But from some preliminary tests (pulling and releasing the handle before the trigger was installed) this gun gets about the same range as my crossbow. In the same vein as the “X-Bow”, “+Bow” and “SNAP-Bow”, and since it’s Langley’s homemade bow, I call it the “L-Bow”.

The next time you read an article about the L-Bow, it will have an awesome aluminum Crossbow shaped frame, and there are plans in the works for an even more awesome paint job. Heres a hint: I’ve been doing a lot of reading on a website called “The Dented Helmet”.

Tags: aluminum, doorfucker, homemade, L-Bow, screen door closer

This entry was posted on Saturday, January 10th, 2009 at 9:30 PM and is filed under R&D. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.