Here on Nerfhaven, people tend not to take you seriously until you have something concrete to show them. So after sitting on an idea for about two years, I finally went ahead and tried to implement it. What follows is a thorough report on how not to build a homemade out of a pneumatic screen door closer. Hopefully someone will be able to improve upon my work and come up with something usable.
A couple of years ago someone on the forums made a comment about the possibility of using a screen door closer (that metal thing that makes the hissing sound and keeps your screen/storm door from smacking you in the ass) as an air reservoir to be used with a semi-auto zero valve. It dawned on me that a door closer was a spring loaded pressure chamber just waiting for a barrel and a trigger mechanism. I immediately ran out and bought one, cut off the air regulator (a loose screw), and slapped a 1/2" coupler on it.
The trigger mechanism was basically the little metal bit that keeps the door open, a flathead screwdriver, and some luck. On testing, it got about the same range as my pvc'ed crossbow (70-80 feet with a slight arc from chest level), but without a workable trigger or a handle, it was useless as anything other than a conversation piece.
-Time passed, I got distracted by other projects, boltsniper appeared on the forums, I stopped nerfing for the most part, etc.
This week I just happened to have some extra time, a new workshop, most of the raw materials on hand, and an excuse to go to home depot for the rest. I took a look at the SNAP and had a couple of chats with Carbon, and worked out a system where I could basically build a SNAP around a door closer and expect it to work.
Two days, a dremeled finger, and a valuable life lesson about beer and powertools later, I had this monstrosity.
From top to bottom, my crossbow, the barrel I use with the crossbow, the doorfucker3000: maimer of hands, the comically huge barrel that it requires (more on that later), and what's left of the cocking arm. The cocking arm--a length of #10 threaded rod--decided to bail on me when I tried to cock the gun one handed by pulling back on only the part of the rod which extended out of the left side of the gun. Right after I riveted the back end of the thing on. Permanently. I can no longer retract the plunger from outside the gun.
Valuable lessons learned from this experience:
-Keep your finger out of the way of the fucking dremel. Your tungsten carbide bit does not merely grind plastic and metal, it is a demoniacally possessed nightmare which spews itchy bits of aluminum at your skin, howls like a banshee, and hungers for human flesh. You know how it rips curly bits out of whatever you're cutting? Yeah. Just think on that a while.
-Don't drink a six-pack of heineken and expect to remember where you set down any of your tools for more than ten seconds, or even weather or not you left them on. Ironically, the injuries stopped after the beer. I just experienced a huge surge in wtf moments and really close calls before I decided to call it a day.
-Pneumatic door closers have a really really powerful spring. So powerfull in fact, that if you put the thickest possible threaded rod through the hole that you're supposed to use to mount the damn thing, it will snap in half. Bracing the gun against my chest and using both hands on either side of the cocking arm was the only way to prevent this.
-Your gun should never have so much rough unfinished metal on it that rapidly cocking it is tantamount to shoving your hand into a blender.
-Some pneumatic door closers work just fine (like the first one pictured). Others inexplicably dump a bunch of under pressured air into the barrel, popping the dart out before it can build up any velocity. Cx's telescoping barrel would probably fix this. Stock darts of the right size in 1/2" pvc might do the trick too, what with the rubber suction cups increasing barrel friction. Using a ludicrously long barrel will work too, but it's probably hurting the range.
-The heavy duty trigger I built for this project could be used as an alternate design to the one Carbon uses for the snap, if you live in a parallel universe where clothespins are made out of jam or if you want to use a four million newton-meter spring in your homemade.
-If Dremel doesn't already make a model with reversible rotation, they ought to. Being left handed, I have to hold mine in such a way that it flings chunks of whatever I'm cutting at my face. By the time I was done grinding the channels into the sides of the guns shell, I had enough white powder down the front of my shirt to make Tony Montana blush.
The point of the project, now that so many other scratch-built homemades are coming onto the scene, was to come up with a design where most of the hard work was already done for you. Making a plunger and matching a spring and a pressure chamber to it would already be taken care of if you use a pneumatic door closer. Unfortunately, the door closer created more problems then it solved. My recommendation is to leave this door closer design alone, but don't let that stop you from finding a better way to use it. Like the perfect whore, it's cheap, available, and won't give you herpes.
Here are some more pictures of the beast
The door closer after disassembly. To attach a barrel, I pretty much just hacked off the mounting hardware and air regulator and glued on a 1" coupler with a 1/2" reducer brushing.
Closeup of the trigger. It was made out of different sizes of aluminum U-Channel. This stuff is meant to be used to frame the edges of different thicknesses of plywood, and can be found by the threaded rod and metal tubing in the hardware section of your local lowes/home depot. I had to grind some of it down with a file to make it all fit. It's held in with a machine screw and the catch it attached with pop rivets.
The end of the door closer. Don't drink and mod, kids.
Closeup of the back end.
Edited by Langley, 04 November 2008 - 03:59 PM.