There are a lot of possible variations on this, I chose to keep the battery outside the box so I could pop it in and out rather than use a separate on/off switch. Another capacitor or a larger one can be substituted and voltage set lower to increase total joules potential but I have found 1000uf at 35v to be just right for welding silver, nickel, nichrome and kanthal 28-34g wires together. Really any old power supply can be substituted for the battery as long as it is within limits of the input voltage for the LM2577 board, I just have 18650 lithium ion batteries always charged and on my nightstand so it is convenient for me to use this form factor.
The cost for the components is right around $25. You can buy bulk wire for about $25 for 250 feet. Commercially available resistance/no resistance wires are available for $1ea and measure 3" long. So with the same $50 investment and a few hours of your time you can make 1000 wires for what it would cost you to buy the pre made ones. Plus, by building your own, you have control over what wire gauge, what material, and what resistance the final wire will be.
This is not my original idea, nor is it the only way to make such a device. This is simply a illustrated guide to build one the way I built mine.
Step 1: Parts List
Batter Holder: BH-18650-W-ND
Project Box: 377-1165-ND
Momentary Switch: 507PB-ND
LM2577 Board: Ebay
Smooth Jaw Alligator clips: 314-1018-ND
Battery: 3.7v or any 3.5v-40v power source can be used
Super Glue and Hot Melt Glue
Shrink wrap or electrical tape
22 Gauge stranded wire, 18 Gauge stranded wire
Solder, flux and Soldering Iron
Two small wire nuts
Step 2: Wire LM2577 and put in place
Solder the resistor to the IN +
Solder a 6" wire to the IN -
Solder the diode (note polarity, black ring faces away from board) to the OUT +
Solder a 6" wire to the OUT -
Line up the LM2577 board to the box and locate where the potentiometer screw is going to be, mark and drill 3/16" hole.
Apply superglue to the 2 capacitor tops on the board and glue in place.
Step 3: Drill Box and Attach Components
Drill box for strain reliefs and insert.
Drill a hole for the momentary switch and secure switch to box.
Use hot melt glue to attach battery holder to outside of box, drill 2 small holes so the wire can be routed to inside of the box.
Add a dab of hot melt glue on the inside of the box where the battery holder wires come through to hold them in place.
Put hot melt glue on capacitor and glue to box with leads facing up.
Step 4: Complete the wiring
Wire the other lead from switch to fuse with a wire nut (this makes the fuse easily replaceable).
Connect other end of fuse to resistor with another wire nut.
Connect diode and one alligator clip wire lead to + of capacitor (the longer lead is the +)
Connect both - wires from LM2577 the - from the battery and the other alligator clip wire lead to the - of the capacitor (the - is the short lead marked with the black strip running down the cap).
Step 5: Testing and finishing up
Hook the alligator clips to your multimeter and push the momentary button, you should see the voltage go up a little and stay steady around 12-14v which is where the boards are set when you get them.
Using a small screwdriver start turning the potentiometer while holding the switch down. If the voltage is not going up, you are turning it the wrong way. Keep holding the button and turning the screw until you get to 35v.
You should have about 0.6 joules of energy stored in the capacitor. Touch the wire leads together and they will short, cause a spark (intended action) and the meter will now read 0v. If everything checks out, then you can add heat shrink or tape to all the exposed connections and screw the box together. If not, double check all your connections.
Step 6: Welding tips
Be sure to keep the ends of the wire as close to the clips as possible.
If your wire has a coating on it, lightly sand the tips to be welded.
Rather than trying to push the ends of the wire together, try to overlap the ends by 1mm for a strong joint.
If you have question or need some help troubleshooting your welder, the best place to get answers is here: http://www.e-cigarette-forum.com/forum/modding-forum/367095-resistance-no-resistance-wire-welder.html
Big thanks to everyone on that forum who helped contribute to this project!