Whats The Toughest/Lightest Metal
 

1

Titanium should be pretty good (At a high cost though)

Generally, it's best to make it out of whatever metal the rest is made out of due to the theory that different metals when brought together will generate more oxidation then similar metals. This may not be a consideration for AEGs though, and if not, have it made out of a quality aluminum, or stainless steel. Considering the size of the piece, weight really isn't a consideration.

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If you want a super tough and resonably light metal you should go with the titanium... but the price tag will be sizeable.
The gun barrel is alredy made out of a low grade alumininum

titanium is over rated you not buillding rocket or air plane. Use mild steel or if it is to havy for you then use T7 aluminum or better yet just buy your self a new tompson becouse to make that peace would cost just as much as getting new gun.

Go with good quality alluminum.

Titanium is also one of the hardest metals to machine. It's right up there with stainless steel in terms of 'machinability'. I'd recommend aluminum since it's really easy to machine and a lot tougher than the metal that they used to cast that piece. Your machinist will love you for it..

it looks like you have a design issue more than a material issue. If you can, radius the inside corner where that finger snapped off. It may be possible to bevel the edge of the part which sits in there so you can put in a 1/8" rad which wouldn't concentrate stress like a sharp corner does.

-_-
 

I'd recommend a good quality aluminium for the ease of machinery, it's light too.

After MadMax mentioned it, it looks like that piece is holding the combined mass of the whole outer barrel. Try doing this (although it might not look 100% like a real thompson).

What you have is this:

............|====================^==
............|=======================
............|=======================
............|----------------/ <-gas tube
|======= <-piece that broke off, the stress point

Ask the guy to machine it like this:

............|====================^==
............|=======================
............|=======================
............|----------------/ <-gas tube
|=========== <-piece that broke off, this way the strees is distrubuted evenly over a greater area

you can get a high grade aluminum with aditives that make it stronger than steel, but it is still lighter than anything else (being aluminum) It is also not brittle like many of the harder metals out there.

When machining this stuff with a ceramic or diamond cutter, the cutter would have to be changed after every other cut, that is how hard it is. They used it/are using it for the solar energy and baha racers being built here at U of W.

Well the stronger than steel promise is actually pretty vague. Steel varies considerably. High alloy aluminium that is forged (not machined) can acheive a strength comparable to unforged mild steel. Machined aluminium does not often get the same strength because it is cut into shape instead of being cold worked into shape. You actually have similar strengths to cast parts because the bulk stock is cast before it's machined to shape.

There are many HSS (high speed steel) cutters cut most alloy aluminums just fine. You don't usually need exotic cutters for aluminium. About the only case where I could see a benifit in superhard cutters is with cutting foamed aluminium. Aluminum can be blown into a very stiff, strong, air filled foam. Cutting it is a biatch because there is a lot of aluminum oxide which is nearly as hard as diamond. You wear out saw blades pretty fast cutting that stuff.

Machinability is also an important design concern for choosing a material. Materials which exhibit incredible mechanical properties but are very difficult to machine are pretty much limited to very high extreme/high value applications (like turbine blades) because making them into anything useful is nearly impossibly expensive.

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I hear ya Carl.

I can't remember what it is called, it's a composite.

I was told of it by one of my instructors, who used to work in the machine shop at UW.

He was given this stuff to make parts for the racer (baha). Incredibly hard stuff, and durable. it exhibits all the same traights as aluminum, except that it is harder than any steel he had attempted cutting before. It may very well have been the foamed steel, with some sort of space-age aditive. I will ask him about it when I return to classes on the 9th.