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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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Clear Combustion Chamber Dilemma

Unread postAuthor: daberno123 » Tue Jul 22, 2008 4:06 pm

Alright my dilemma is the material used for the chamber.

The two options are 4" clear pvc and 4.5" OD polycarbonate tubing with 1/8" thick walls. I can get both in 2' lengths for about the same price. Both will be used with 4" pvc fittings, the polycarbonate would be glued with epoxy and the pvc with (duh!) pvc primer+cement

My questions are:

1. Is the polycarbonate tube going to be stronger than the pvc? I've heard the stuff is unbreakable. Or is it overkill?

2. Is the blue tint of the pvc going to make it any harder to see the flame front? The polycarbonate is perfectly clear, no tint.

The planned gun will be fully advanced, with metered propane, fan, multiple spark gaps, etc. Which would you guys choose if you had the choice?

EDIT: Added some info
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Unread postAuthor: Fnord » Tue Jul 22, 2008 5:07 pm

1. Probably, yes. Polycarb is shock resistant, which is good for a combustion gun. Pvc isn't.

2. No. In a dark area you could probably even see it through a light coat of spray paint.

I'd use a few screws in addition to epoxy.

The planned gun will be fully advanced, with metered propane, lighted LED fan, multiple spark gaps, etc.


Fixed ;)
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Unread postAuthor: sirspuddest » Tue Jul 22, 2008 5:11 pm

Given a choice between the two, I'd go with the PVC, simply because it's pressure rated (and for tradition's sake), but I don't see anything wrong with polycarbonate.

It's got a high tensile strength, and it's very resistant to just about everything, including heavy impacts, extreme temperatures, and fire.
On top of that, it's super clear - like fish tank glass.

I think either one would be a pretty safe bet. But, like I said, I'm a traditionalist, so I'm more inclined to choose PVC.
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Unread postAuthor: daberno123 » Tue Jul 22, 2008 5:19 pm

Already thought of the lighted LED fan Fnord. I'm going to get a blue one like this and paint the gun a matching blue. Bolts are a good idea too.

Right now I'm leaning towards the polycarbonate tube, even though it will be a little more expensive. It'll be stronger, not as likely to break. plus has the cool factor of telling people the chamber is polycarbonate 8)
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Unread postAuthor: DYI » Tue Jul 22, 2008 5:31 pm

The only reason I'd be worried about the polycarb is that its walls are only half the thickness of the PVC pipe's walls. On the other hand, combustion guns don't even approach the failure pressure of a well made SCH 40 PVC pipe, so the polycarbonate should be fine, as well as being less susceptible to horrible shrapnel-filled explosions, and more rugged.

Also, the polycarb should be cheaper. What do you plan on using for fittings on the chamber? Are you just making them out of polycarbonate plate? Because that would be really kickass.
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Unread postAuthor: daberno123 » Tue Jul 22, 2008 5:46 pm

For fittings I was just planning on using normal pvc fittings since the OD of the tube (4.5") is the same as 4" pvc. Although a polycarbonate plug (with o-ring) bolted onto the back end is an option I'm looking into. The front end I'll probably just stick to pvc fittings since I would have to get the plate machined to have 3" NPT threads for the camlock I plan on using.

However, I might look into getting some clear pvc fittings cheap from an ebay seller. :D

Overall the gun should be pretty kickass when finished.
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Unread postAuthor: ramses » Tue Jul 22, 2008 7:36 pm

I will hunt you down if you go with pvc and use purple primer.:twisted: :twisted: :twisted: :twisted: :twisted: :twisted:

Does anyone want to make a polycarb hybrid?? :lol:
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Unread postAuthor: daberno123 » Tue Jul 22, 2008 8:22 pm

ramses wrote:I will hunt you down if you go with pvc and use purple primer.
Does anyone want to make a polycarb hybrid??


I wouldn't dare use purple primer, but I'm probably going with polycarbonate. If I do use all polycarbonate fittings I'd probably try 2x in it :D
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Unread postAuthor: SatansEvilTwin » Tue Jul 22, 2008 8:26 pm

whats in ur pic daberno? Looks like one of Chimaira's CD covers but its too blurry to tell
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Unread postAuthor: SpudFarm » Tue Jul 22, 2008 8:38 pm

i mentioned the clear hybrid to DYI but he killed my idea :(
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Unread postAuthor: daberno123 » Tue Jul 22, 2008 8:58 pm

Its the album artwork from the album "What Demons Do To Saints" by the band Beneath the Sky. They are from my city and one of my favorite bands. :D

I've been looking into getting polycarbonate fittings from sheets and it might happen because Mcmaster has a sample pack of 6"x6" 1/4" sheets for a ridiculously low price ($2.55). This means I'm almost definitely making a back plug, provided I can find a 4-1/4" hole saw.

Does anyone know of a clear epoxy or similar strength adhesive so I could glue 3 or 4 of these sheets together and still keep the optical clarity?

I'm also going to look into making a plug for the front and then getting 3" NPT machined into it.
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Unread postAuthor: SatansEvilTwin » Tue Jul 22, 2008 9:30 pm

Nice.. theyre pretty good, I just listened to "7861" on youtube
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Unread postAuthor: iisthemuffin » Tue Jul 22, 2008 9:56 pm

Im not sure daberno, but wouldnt a clear glue still try kind of cloudy?

Well cloudy compared to the clear pipe i wouldnt think.


I generally like very heavy music, but i would have to say this band is garbage. The musician ship is amazing, but that singer does them no justice. If you call that singing. And im not just saying that because hes screaming. I like screaming music as well. But hes no good.
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Unread postAuthor: daberno123 » Tue Jul 22, 2008 10:12 pm

I think I have found some glue that chemically welds polycarbonate together.

http://www.craftics.com/products.cfm?Category=80

Says it dries clear too.

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

But I found a machine shop near me who I'm going to get a quote from. If its not too expensive I'll be on my way to building the first polycarbonate spudgun AFAIK. :D

@iisthemuffin
Although I really do like the band, and the instrumentals are great the one thing I would change is the singer. I wouldn't go as far as saying he's no good, but I definitely think they could use a better one. Ah well, I'll probably be changing it to the album artwork of "Elephant Shell" by the Tokyo Police Club, a band I've recently taken a liking to.
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Unread postAuthor: iisthemuffin » Tue Jul 22, 2008 10:21 pm

Ive heard of them. I might just go have a listen. Ive been meaning to look into them but always forget. Thank you for reminding me.

And 800 is a little crazy. I hope the shop near your house will offer more suitable prices.

You could, like you said, use pvc fittings. May be your best option if you keep getting prices like that.
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