SpudFiles

i am working on a new air rifle and to save space i want to machine the air chamber, but i don't have large threads and no welding equipment. so if i machined out a tube could i make endcaps and solder them one like i would with copper tubing? or is there a better way to secure them?
these are the materials i have to work with (in order of preference)
Aluminuim
steel
brass

Sounds like a good idea you got there but a first a few things:
its nigh on impossible to solder aluminium because it oxidises so fast and its hard to find a flux for it.
As for steel- brazing would work, that is if you could get it hot enough!
And brass which in my opinion would be your best bet, is fairly easy to braze and can even be solder jointed to copper in some cases so that would probably work best.

Except brass is much more expensive.

Use steel and braze it.

You can reliably do this if your wall thickness is not too great (like around 1/8"-3/16" max) with a regular old bernzomatic map/pro gas torch kit, and the bronze brazing rods that are usually sold next to it on the shelf in your local big box home improvement store.

If your chamber is thicker than this (thicker than 3/16" appx), you will either need to be very patient and precise with your torch hand, or you'll need to get a real oxy/fuel kit.

I'm not too sure about the brazed aluminum holding up in a situation where it serves as a pressure vessel... I would be a little weary of that and tend to leave brazed aluminum more for structural quick fixes.

mobile chernobyl: if its thick, do like i do. Chuck it in your forge

Hmm, i don't know about brazing aluminium, but didn't BtB just show us aluminium welding rod's

thanks guys. as im sure you know aluminium is a dream to work with on a lathe. thanks for your help. i will most likely use steel because large peices of brass are expensive as hell. i always have horrible experiences with epoxy so im trying to avoid using that unless you know of any really strong epoxies i could use?

jakethebeast wrote:mobile chernobyl: if its thick, do like i do. Chuck it in your forge

Hmm, i don't know about brazing aluminium, but didn't BtB just show us aluminium welding rod's

I'd still be keen on the strength of an aluminum braze in the use of a pressure vessel, not unless you have a type of weld that can really take advantage of a lot of surface area.

I just went out and tested how easily it is to weld using just an oxy/fuel setup. (after watching a quick video on youtube for setup parameters...)

It's amazingly easy to weld steel using purely oxygen and fuel, the trick is all in the flame setting and keeping your welding rod in the middle flame (so it doesn't rapidly oxidize between "dabs"). The flame itself should be completely neutral.

I also tried oxy/fuel welding aluminum and while I can do this meagerly with a GTAW setup, you really need the correct stuff for aluminum. There is just about only 1 flux specifically designed for O/F welding of aluminum anymore in 'merica (or so I read) and anything else results in the flux contaminating the weld by being pulled in unlike a steel braze.

One thing to note - having prior GTAW welding experience on steel made it alot easy to know when to "dab" and when to "swirl" with the filler rod and flame respectively.

Here's some examples of what you can do with O/F on steel in about 5 minutes lol.




I did manage to get a "pretty" weld on a thicker piece of steel, but unlike GTAW, O/F welding needs the element to be preheated (well ok, GTAW of really thick pipes needs preheating too... I'm talking .25" or less tho) so the HAZ of the weld becomes larger and its really hard to keep a small line of dime droppings. However it is pretty smooth if you work it right and is certainly a good weld!

nicely done. there are times when i really wish i had welding equipment, but lathes and mills certainly can make pretty things

True, but welding gear doesn't cost that much, i actually find mine, it was someones trash and i fixed it, it work's like a charm

I bought mine second hand. You do want an oxy/fuel setup for thicker materials. Use a neutral flame for welding and a slightly carborizing flame for brazing,

I have seen it on here but u can try durafix to weld aluminium have not tryed it I have a welder for steel and alum can buy it on eBay

alright thanks. what would a good wall thickness be for high pressures like 300-500 psi

Need to know the material and its "condition" to answer that.

I've used 7/8"od x .065" wall normalized 4130 seamless tubing for pcp's @ 3000psi working pressure...safety factor is ~3x @ yield.

Google barlows formula, remember to build in a safety factor.

Important to keep in mind that heating materials for welding/brazing will likely alter their properties from something "known" to something "unknown". Assume the worst case until you know better.

If you've a lathe and mill, you could consider sealing with an o-ring and counter sinking QUALITY screws in shear. Brand name low head socket head cap screws are a good choice. I buy them by the box. (100)

This construction method is easy to do, strong, and easy to calculate the strength of.

As for construction materials, although I will use aluminum for some things, for "more stressed" components, I prefer steel (1045 and 4130) and brass.