First big cheap combustion gun build

[88pathoffroad]

I previously built a gun with a 3"x10" chamber and a 38" 1.5" barrel; it shoots spuds pretty well, so I decided to go one step bigger. Couldn't resist. I'm using propane from a trigger torch for fuel and self-regulating it by counting, heh. Planning on building a regulator setup sometime soon.

I don't have a lot of cash lying around, so I went as low-buck as possible, using a lot of things I had on hand already and buying what I needed as I went. Hopefully this will be a safe, reliable gun that will respond to upgrades down the line. (spark strip and stungun ignition)

I used all-black 4"x10" foamcore ABS for the chamber, ABS adapters, BBQ ignitor with dual-spark screws spaced approx 1/3-up, 1/3 down 90 degrees apart, a spare 2" CPU fan on standoff bolts in the cleanout cap, 9V battery holder with custom blue LED indicator and micro-switch, 2"x5' foamcore ABS barrel and 1.5"x5' PVC barrel. All screws and bolts are epoxied on the outside and superglued inside. I also epoxied the joints on the chamber because the cement didn't seem to do a very thorough job after drying(there were bubbles and small holes at the seams). All wiring is soldered at joints and connectors.

I'm hoping using the foamcore ABS wasn't a huge mistake, I planned on taping the combustion chamber up with a roll of electrical tape just to err on the side of safety. There was no standard PVC available locally in shorter lengths, I would have had to buy a 10' stick of 1.5", 2", and 4" pipe which adds up quick! Total cost on this was around $40 in pipe and adapters, BBQ ignitor and glue/primer. I have enough pipe left over to build another one and possibly sell off to get some cash back, heh.

Keep in mind this isn't quite finished yet, I know there's a sticker to be removed and the barrels haven't been chamfered and I haven't fired it yet...

On to the pics!











And one of my little gun. (shoots about 200-300 feet as far as I can tell)

[CasinoVanart]

I can hear the vultures already. What you have made is an accident waiting to happen IMHO.
What possesed you to use such crappy materials?
Don't say money either- if you can't afford to make it safe please don't make it bro! It won't blow up straight away either, but it will eventually.

Be carefull and film it!! (jk)

[mark.f]

I can hear the vultures already. What you have made is an accident waiting to happen IMHO.
What possesed you to use such crappy materials?
Don't say money either- if you can't afford to make it safe please don't make it bro! It won't blow up straight away either, but it will eventually.

Be carefull and film it!! (jk)

Evidence? I happen to have plenty of evidence to the contrary. Please don't scaremonger people.

The ABS is fine. Plenty of people have used foamcore ABS (also known as cellular core) for combustions. SpudBlaster15, Pete_Zaria, and plenty others that don't pop into mind now.

I think the design is good. There's no need to wrap the whole thing in electrical tape, either. If the ABS decides to go, it will rip rather than tear, and the electrical tape wouldn't do anything to help it.

The ignition could use a little cleanup, but that's completely up to you. You can install a 3/4" PVC handle, or you could just run the wires through some flex-tube.

And is that LED on the 9v battery holder wired directly in series with the fan? If it is, what type is it?

[88pathoffroad]

I can hear the vultures already. What you have made is an accident waiting to happen IMHO.
What possesed you to use such crappy materials?
Don't say money either- if you can't afford to make it safe please don't make it bro! It won't blow up straight away either, but it will eventually.

Be carefull and film it!! (jk)

Hmmmm, this thread seems to indicate ABS cellcore is a warranted material to use...

http://www.spudfiles.com/forums/cellula ... 15569.html

Like I said, I didn't need 30 feet of pipe laying around my house...the ABS was available in 2-foot and 5-foot lengths.

[88pathoffroad]

The ABS is fine. Plenty of people have used foamcore ABS (also known as cellular core) for combustions. SpudBlaster15, Pete_Zaria, and plenty others that don't pop into mind now.

I think the design is good. There's no need to wrap the whole thing in electrical tape, either. If the ABS decides to go, it will rip rather than tear, and the electrical tape wouldn't do anything to help it.

The ignition could use a little cleanup, but that's completely up to you. You can install a 3/4" PVC handle, or you could just run the wires through some flex-tube.

Well it IS a first edition, heh. Cleanup is coming.

And is that LED on the 9v battery holder wired directly in series with the fan? If it is, what type is it?

It's wired with the switch, but not inline with the fan circuit. 5mm 8k mcd blue LED I scored on Ebay(bag of 50, 99 cents + ship) ...390 ohm 1/4W resistor should work fine with a 9V battery and it's STILL pretty damn bright.

[starman]

Not sure where you are located, but Home Depot and Lowes sells short 2' and 5' sticks of pressure rated PVC.

You'll probably be ok with this spray a pray model, but cell core materials are considered bad practice when building a spuddy. Also, with your performance hop ups, your fan and dual spark gaps, will raise the pressures in the chamber somewhat beyond that of a basic one gap, no fan spray and pray.

[ALIHISGREAT]

i would use the foam core ABS over Pressure rated PVC as ABS doesn't create shrapnel if it fails, it just tears/splits also ABS doesn't suffer from Sunlight or the cold.

[DYI]

The ABS is fine. Plenty of people have used foamcore ABS (also known as cellular core) for combustions. SpudBlaster15, Pete_Zaria, and plenty others that don't pop into mind now.

I'm pretty sure that they all use solid-wall ABS, as I do. Actually, I can almost guarantee that SB15 uses solid-wall, because cellular core anything is pretty hard to find in the northern regions of Canada. Cell-core ABS is pretty much an artifact of the USA, and it seems as though half the members here think that ABS is automatically either cell-core, or the unobtainable pressure rated variety of solid-wall.

On the downside, that chamber is likely to fail at some point. On the upside, you probably won't be hurt very badly, or at all, when it does. I'd recommend solid-wall ABS for a material if you rebuild it after it fails - the lowest pressure I've got that stuff to fail at was over 400psi, and that was with the application of a fairly heavy shock load.

[88pathoffroad]

Not sure where you are located, but Home Depot and Lowes sells short 2' and 5' sticks of pressure rated PVC.

You'll probably be ok with this spray a pray model, but cell core materials are considered bad practice when building a spuddy. Also, with your performance hop ups, your fan and dual spark gaps, will raise the pressures in the chamber somewhat beyond that of a basic one gap, no fan spray and pray.

I went to both Lowes and Home Despot and neither store had short lengths of PVC. Ten-foot sticks is all they had. For short length pipe all they had was cellcore ABS, so that's what I got.

I ran 10 lbs of spuds through it yesterday, seems to work just fine. Nice bang, the spud disappears and it's ready to go again. The only thing I regret was not going the breech-loading barrel route. Stuffing 5 feet of barrel is tedious and downright impossible if the spud fits too tight.

A new build may be in order...perhaps I can find some short lengths of 4" PVC somewhere on a jobsite, heh. Also, I won an Ebay auction for a 200k volt stungun...$11.51 shipped. Woohoo!

[starman]

I went to both Lowes and Home Despot and neither store had short lengths of PVC. Ten-foot sticks is all they had. For short length pipe all they had was cellcore ABS, so that's what I got.

Are you in Canada or a far Northern state? Those items are standard in all those stores I've been in in the Southeast. ABS is more prominent in the colder zones.

Try a commercial plumbing supply outlet.

[88pathoffroad]

I'm in Oregon. I'll have to visit the plumbing supply place some time here and see about getting the good stuff for my next build.

I've run another 20 lbs of spuds through it and I seem to be getting between 500-700 feet if my estimation skills are any good. I've recorded one shot of 550 feet with a GPS.

Also went out and found some nice Krylon Fusion spraypaint in bright orange. If it doesn't rain, I may have a big orange toothpick by the end of the weekend. I may try my skills with a fine paint brush and do a bit of detail work as well.

[starman]

I've run another 20 lbs of spuds through it and I seem to be getting between 500-700 feet if my estimation skills are any good. I've recorded one shot of 550 feet with a GPS.

That's about the limit of flight distance for a spud no matter what kind of cannon you have. Drag dominates and thus limits it's ultimate performance.

[mark.f]

Actually, I believe SpudMonster's cannon (identical name) shot around 1,000-1,100 feet with a 2" potato slug (it was even made of ABS as well).

It's not on Spudfiles, you'll have to look in the Archive. One moment please...

EDIT: Long Link