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Clear Combustion Chamber Dilemma

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: DYI » Tue Jul 22, 2008 10:24 pm

Also i just mocked up the front bushing in eMachineshop, but the cost came out to nearly $800 dollars. :shock:


Never, ever get your work done at a machine shop unless you use 100 dollar bills as kindling. Find a more creative way. Right now, I'm thinking flange-type fittings rather than threaded ones, using polycarb plate, epoxy to attach the plates to the pipes, and bolts to hold them together. Really, you could probably whip that together yourself if you had a drill press and some determination.

If I really need a lathe, I just wait until I can get some time in the metalworking shop at school.

i mentioned the clear hybrid to DYI but he killed my idea


I did? I don't even remember that. Thinking of it now, it might be a fun little project to work on. Done on a mini scale, you could just bore it out of polycarb bar stock, and use normal pipe taps for the threaded connections. Now we just need to get Larda to start selling 3000psi rated clear unions...
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Unread postAuthor: daberno123 » Wed Jul 23, 2008 6:00 pm

I've been trading emails with the president of a local machine shop and he said he could get it done for $50-$100. I'm still waiting to hear back on whether or not this includes labor. Sounds reasonable but still thats a bit expensive.

The flange idea is a good one, but the bolt circle on 3" flanges is 6" in diameter, far above the pipe diameter I was planning on using. However, 7" OD polycarbonate tube isn't too expensive, and would accommodate the 3" flange... Something I'm thinking over.

Also, does 1/2" polycarbonate sheet seem thick enough to use for the fittings?
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Unread postAuthor: DYI » Wed Jul 23, 2008 6:39 pm

The flange idea is a good one, but the bolt circle on 3" flanges is 6" in diameter, far above the pipe diameter I was planning on using.


Not quite sure what you're talking about here...

Just make a flange with two 8" or so circles, attach one circle to the chamber (via epoxy / polycarb glue), and one circle to the barrel. You can actually buy precut polycarbonate disks from McMaster-Carr.

And $50 - 100 doesn't sound bad at all. Nowhere near some of the ridiculous quotes I've heard. Did you tell the machinist what you plan on building? That would definitely help.
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Unread postAuthor: daberno123 » Wed Jul 23, 2008 7:00 pm

I think I might have changed my mind on a few design specs.
[Disregard]
The chamber will now have a 7" OD and 6.75" ID.
The back plug will be 1" of polycarbonate plate (alright 2 .5" sheets glued together)

DYI, I thought you were talking about the flanges you can buy, not homemade. Still your comment provoked my thoughts and I think I will use a 3" steel flange bolted to a 1/2" thick polycarbonate disc 6-3/4" in diameter. The flange is 7" in diameter, so it will be flush with the outside of the chamber. Copious amounts of epoxy and bolts will be used to hold it in place.
[/Disregard]
Of course this could all change once I get an email back confirming the price of machining.
I'm having difficulty deciding :cry:

EDIT:
OK, scratch everything above. I've gotten an email back from the machine shop confirming the front bushing can be done for under $100, possibly as low as $50. :D

I will now be using 4.5" ID polycarbonate tube w/ .125" walls. Back plug will be made of four 1/4" polycarbonate sheets glued together and cut with a hole saw on a drill press. The front bushing will be made of six 1/4" polycarbonate sheets glued together and cut in the same way, then it will get 3" NPT threads cut into it for a camlock.

HGDT predicts 1052 ft. lbs of muzzle energy and 818 fps with a ten foot GB barrel at 1x.
At 2x with the same barrel it predicts 1975 ft. lbs of muzzle energy and 1120 fps which I believe is faster than the speed of sound. :D :D

EDIT #2: crap, sos is 1129fps :evil:
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Unread postAuthor: jimmy101 » Thu Jul 24, 2008 4:59 pm

daberno123 wrote:At 2x with the same barrel it predicts 1975 ft. lbs of muzzle energy and 1120 fps which I believe is faster than the speed of sound. :D :D

EDIT #2: crap, sos is 1129fps :evil:

No, SOS is not 1129fps. SOS is no particular number since it is temperature and humidity dependent.

SOS is 1087 fps in dry air at 32F.
SOS is 1120 fps in dry air at 68F.
SOS is 1145 fps in dry air at 86F.

Besides, GGDT probably isn't accurate to 1%. If you want to make sure you get to SOS (or at least make a valiant effort) then just run the gun at a bit above 2x.
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Unread postAuthor: daberno123 » Thu Jul 24, 2008 5:07 pm

Thanks jimmy, 1129 was just a number I pulled off google. SOS wasn't really something I was aiming for, I just noticed that it was close in HGDT. Still, I have a chrony so if I wanted to I could try and break it.
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