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my first spud gun

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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my first spud gun

Unread postAuthor: mrbadexample » Thu Oct 09, 2008 3:52 pm

Image (click to enlarge)

my first spud gun, multiple interchangable barrels.
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Unread postAuthor: Pilgrimman » Thu Oct 09, 2008 4:11 pm

As for construction and design, I like it a lot! The only problem is (from what I can see) that you used DWV threaded connections on the barrels, which are not pressure-rated. This is not a huge problem, as the barrel doesn't bear load for a long time, but you may have problems with the fittings cracking due to the stress induced by the barrel sagging. A quick trip to the Spudfiles Wiki will give you all the knowledge you need to determine pressure-rated materials from non-pressure-rated ones. In this case, I could tell due to the depth of the reducer bushing in the threaded fitting's slip socket.

Other than that, this is a very nice build! I particularly like how you compensated for changes in diameter with varying barrel lengths for maximum efficiency! Well done!
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Unread postAuthor: mrbadexample » Thu Oct 09, 2008 4:15 pm

thanks, i designed it last year while in a time of unemployment, saw my first spud gun on youtube a year and a half ago, did a little research, ran the numbers. as soon as i got "income" i slapped it together.

all the threaded fittings are schedule 40 (imprinted in the molding)(i've seen youtube vids where spud guns go bad) and not drain type PVC, they were only a few cents more than drain/waste fittings. i've been using the 1.5" barrels for a year, no problems, the 1" and 2" barrels haven't been used yet. will use those maybe this weekend :D
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Last edited by mrbadexample on Thu Oct 09, 2008 4:28 pm, edited 1 time in total.
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Unread postAuthor: Pilgrimman » Thu Oct 09, 2008 4:19 pm

I may be wrong, I guess. One thing I know, however, is that SCH is not a pressure rating, but a wall-thickness rating. You probably know more about your own cannon than I do, though. Still, its a nice build! :D
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Unread postAuthor: mrbadexample » Thu Oct 09, 2008 4:37 pm

Pilgrimman wrote: This is not a huge problem, as the barrel doesn't bear load for a long time, but you may have problems with the fittings cracking due to the stress induced by the barrel sagging.


barrel sagging is not a problem, with my design, the combustion chamber rests in the crook of my right elbow, i hold the sparker loosely in my free right hand and support/hold the barrel and aim with my left hand, so next to no stress :D
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Unread postAuthor: MrCrowley » Thu Oct 09, 2008 4:51 pm

Pilgrimman wrote:I may be wrong, I guess. One thing I know, however, is that SCH is not a pressure rating, but a wall-thickness rating. You probably know more about your own cannon than I do, though. Still, its a nice build! :D
No you are right. Seeing as you can get DWV SCH 40 and Pressure rated SCH 40, the SCH rating has little to do with the pressure rating.

What you need is 'NSF-PW' or a PSI rating. The common misconception on the internet that most spud gun websites apart from Spudfiles tell you, is that if your fittings are SCH 40, they are pressure rated. This is wrong.

mrbadexample,
Read this:
http://www.spudfiles.com/spud_wiki/inde ... sure_rated

:)
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Unread postAuthor: mrbadexample » Thu Oct 09, 2008 5:17 pm

well, i have done a bit of shooting with this gun and feel totally confident with it's construction and integrity. i used mainly barrels # 2 & 4, #1 & 5 are new constructs.

http://www.youtube.com/watch?v=OqBfxPMP_9E
http://www.youtube.com/watch?v=W_rRYnBouis

all my joints are "in line", no directional change of flow, minimal stress is induced, if i made a folded design, there would be two 90 degree angle changes of force/flow. a slight "pull" will be induced on the threaded joints, and only for a few milliseconds, and as stated by your own posting, combustion guns rarely go over 75psi...

i just ordered parts for my first pneumatic gun, i might go copper with it, so the valve will be the weak point in it's construction.
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Unread postAuthor: starman » Thu Oct 09, 2008 5:31 pm

You get extra bonus points for having the guts to put Tiny Tim's "Tip-Toe Through The Tulips" as your backing music in your video...seriously. I haven't heard that in years!!

All that and the DWV aside, this is a decent starter combustion with some obvious thought put into your project. There's more you can do though. Stick around and further your research.

Welcome to Spudfiles!
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Unread postAuthor: mrbadexample » Thu Oct 09, 2008 5:56 pm

thank you!

i intend to stick around and learn more, my entire spud gun education was via youtube.

i was told by bikers that i got "balls" to drive a "smart car", so i must have "super balls" (smarts are 8ft long pieces of plastic powered by 3 cylinder mitsubishi engines) my only improvement on that would be to paint it pink, I'm not going there!

i want to push the envelope in spud gun technology, and i'll need all the help/advice i can get.
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Unread postAuthor: mark.f » Thu Oct 09, 2008 6:27 pm

mrbadexample, nice cannon. It actually is functionally similar to my first cannon, but it just has more barrels. Any more specs on the launcher, besides overall dimensions?

And I still don't get all of you people slamming DWV on combustions!? Ever since I joined the hobby, DWV fittings and pipe (as long as they were SOLID cored) were perfectly acceptable for use in combustion cannons. As of late, though, all I hear everybody somebody posts a perfectly fine combustion in the showcase is "nice but there is DWV". If you guys can unearth any accidents attributed to the use of SOLID-CORE SCH-40 DWV pipe and fittings, I will retract my remarks.
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Unread postAuthor: Pilgrimman » Thu Oct 09, 2008 6:50 pm

And I still don't get all of you people slamming DWV on combustions!? Ever since I joined the hobby, DWV fittings and pipe (as long as they were SOLID cored) were perfectly acceptable for use in combustion cannons. As of late, though, all I hear everybody somebody posts a perfectly fine combustion in the showcase is "nice but there is DWV". If you guys can unearth any accidents attributed to the use of SOLID-CORE SCH-40 DWV pipe and fittings, I will retract my remarks.


All I meant by my earlier statement was that the fittings were DWV, not that they are not suitable for use in this case. I was more of the opinion that barrel sag would crack them due to the smaller sockets, so that's why I brought them up. Clearly, as evidenced by the creator's response, I was wrong. However, that was my reasoning behind bringing up DWV.
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Unread postAuthor: mrbadexample » Thu Oct 09, 2008 7:07 pm

until a failure... what can you say?
my gun has functioned flawlessly with static guard or propane. my chamber failed with "white rain" after a dozen shots, too much water fouled the chamber.

my ignition system is a weber 3613 replacement ignitor ($10 at home depot), two #10 x 32 x 2" machine screws are for ignition, 11" wire ties keep the wires safe and easy to use (around 3" outer fittings) outside of the chamber.

i'd stake my life on my designs. i hold it next to me as i fire it.
you will notice i put the igntion screws towards the back of the chamber, reinforced by the end cap assembly.

i bought a 150KV stun gun for future ignition systems. but i have found using propane and a weber sparker is quite sufficient for performance.

it's a simple design and it works...
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Unread postAuthor: mark.f » Thu Oct 09, 2008 7:55 pm

Hey badexample, I was protecting your design, not slamming it! :wink: When I get my site back up I'll show you what my first one looked like (it was almost the same as yours except for aesthetics).

Pilgrimman, I was commented on a lot of people, not you. Just a general trend that I don't like.
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Unread postAuthor: MrCrowley » Thu Oct 09, 2008 10:21 pm

markfh11q wrote:Pilgrimman, I was commented on a lot of people, not you. Just a general trend that I don't like.

I wasn't bashing his use of DWV either, just saying because i'm not sure if you were talking to me as well :P
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Unread postAuthor: i-will » Thu Oct 09, 2008 10:56 pm

i like that u use more than one barrel. have u looked into a quick connect system for them. that would make it much more awesome.
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