Steel pipe questions

[ramses]

some people make epoxy plugs in side male end caps
and have there spark gap(or spark plugs from cars)there.

You will need two wrenches, or a wrench and a vice large enough (I had to go to my dad's shop to put my 2" together.

Sparkplugs JB welded into bushings make nice ignition systems, the downside is that the chamber can sometimes be "hot", giving you a shock instead of firing the gun. They are made to withstand hundreds of shots from a full auto, ~12x hybrid.

[kjjohn]

found most of the parts I'll need on McMaster, but the pressure ratings are a little confusing. I already asked about the large pipes and got a good answer, but after looking at the small fittings, I found that most aluminum and steel fittings (elbows, reducer, etc.) are only rated for 150psi. Considering that this cannon will produce between 300 and 500 psi, will it be safe to use these fittings?

[Reactor4]

yes, the pressure produced from combustion inside the cannon will be at high levels for milli seconds, the pipe fittings can also withstand more than they are rated for, and the rating is based on a constant pressure at specific temperatures. You'll be fine.

[kjjohn]

thanks for all the help, hopefully you'll see my hybrid in the showcase within the next few months.

edit: Actually, I have one more question. I am planning on having a compressed air tank on board the hybrid so that I don't have to go to the compressor for each shot, but I can't find any air tanks that are cheap enough or light enough. I was thinking I could maybe just use steel pipe, but it would have to be able to withstand up to 400psi continuously for long periods of time (until it ran out of gas). Would it be safe to do this, or would the high pressures cause it to fail?

[D_Hall]

2" sch40 aluminum, assuming it is the standard 6061-T6 will easily handle 500psi.

However, be advised that welding 6061-T6 will make it MUCH weaker. So if you're using threaded fittings, fine, but if you're welding do NOT use the rated pressure (if there is one).

[Reactor4]

it should be fine to use steel pipe as an onboard air tank. you might want to look at the sch.80 steel pipe on McMaster, as it will provide a safe rating for 400 psi, along with the use of corresponding fittings. (on mcmaster, when you go to the fittings page for steel, you can select sch. 80 when you click on the type of fitting you want. The fittings' catalog page will also tell you the rating, as you probably know.) Glad to help!

[kjjohn]

However, be advised that welding 6061-T6 will make it MUCH weaker. So if you're using threaded fittings, fine, but if you're welding do NOT use the rated pressure (if there is one).

Brazing aluminum will not have the same effect, will it?

[kjjohn]

Will 3" schedule 40 steel pipe be able to withstand a burst of 900-1200 psi? (not continuosly, just the combustion pressure)

[D_Hall]

Brazing aluminum will not have the same effect, will it?

While I've not done the research, I would be *shocked* to learn that it doesn't have the same effect. In the event that sentence was unclear due to the use of negatives I'll restate: Yes, I believe brazing aluminum will have the same weakening affect on T6 aluminum that welding has (but can't swear to it since it's not a problem I've expressly studied).


edit: Did some googling. My google-fu is weak and I didn't find exactly what I was looking for, but I did find that welding 6061-T6 reduces it's strength by about 25-30%.

[kjjohn]

I just discovered that I can buy aluminum pipe for about 1/4 the price on Speedymetals than I can on McMaster, but it isn't threaded. How do I put it together since aluminum cant be welded or brazed? Could I possibly use a metal filled epoxy?

[xequa]

Any ideas on where to get 3" steel pipe? I'd like to make a full steel cannon so it'll withstand the pressure of launching a 2.5' long slug of drywall cement. But with that kind of weight, I'd like the whole gun to be made of steel so that safety is well in hand. Any ideas?

[ramses]

mcmaster...

If it's pneumatic, you can probably get by with good barrel braces and some kind of "stock" to distribute the recoil from the back of the cannon to whatever.

[metalmeltr]

I just discovered that I can buy aluminum pipe for about 1/4 the price on Speedymetals than I can on McMaster, but it isn't threaded. How do I put it together since aluminum cant be welded or brazed? Could I possibly use a metal filled epoxy?

Aluminum can be welded. All you need is a MIG or TIG welder. If you have more welding quetions go to the forum at www.millerwelds.com

[ramses]

welding and probably brazing reduces strength 30%.

You could try to find or make compression fittings, or solder it.

or epoxy, especially if this is a pneumatic.

[Moonbogg]

If you aren't welding, use bolted connections OF COURSE. Please do not glue your hybrid together and expect to live.