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Old 03-05-2015, 18:45   #46
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

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Originally Posted by ForSeTi View Post
Question for any metal techs out there

I'm building a Scarab Trimaran.
Working on the rudder atm, and it requires a SS Tube, 33,8mm OD, 6,35mm wall.
As a privat person, I cant get these dimensions in the length I need (I need like 1200mm, minimum amount I can buy is 6meters, which would be a bit costly)
Question now is, does a full 6061-T6 aluminium bar with dia 35mm be a good replacement for the SS bar?

Thanks

G

Yield is about 1/2 for Aluminum; weight is about 1/3. Personally, I would use SS. Even if the aluminum bar is solid, not much additional strength is realized. The moment of inertia (in^4) is proportionate to the power of the radius. Adding material back in to decrease the ID has little effect.
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Old 03-05-2015, 19:46   #47
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

Titanium costs approximately 3 times red brass.
Titanium Prices and Titanium Price Charts - InvestmentMine
Red Brass Price $US / Lb, United States & North America Brass/Bronze Prices

Except for cost, itanium would be better than stainless, as it does not corrode in seawater, unlike stainless, which has other problems, especially when welded and sealed off from oxygen.
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Old 03-05-2015, 20:26   #48
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

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Originally Posted by Terra Nova View Post
Titanium costs approximately 3 times red brass.
Titanium Prices and Titanium Price Charts - InvestmentMine
Red Brass Price $US / Lb, United States & North America Brass/Bronze Prices

Except for cost, titanium would be better than stainless, as it does not corrode in seawater, unlike stainless, which has other problems, especially when welded and sealed off from oxygen.
Note that the brass price is for scrap, but the titanium is for investment quality which drives price up. Even so...

$1.90/lb for red brass - .299lbs/in^3
$5.60/lb titanium - .164lbs/in^3
$0.77/lb 316 stainless - .29lbs/in^3

Assuming I did the math correctly (always an issue) this tube has a metal volume of 21.35cubic inches

If we make it out of red brass that's 6.38lbs, or about $12
If in titanium it's 3.5lbs or $19.
316 stainless its 6.19lbs or $4.76

Somehow I don't think scrap prices are really relavent to what we are talking about here.


The problem with titanium is not price, it's stiffness. The tube would need to have a substantially larger OD than stainless to work the same. Which of course negatively effects the thickness of the foil necessary to contain it. Admittedly its corrosion resistance can't be touched. Except by carbon fiber which also wins on weight and stiffness.
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Old 03-05-2015, 20:37   #49
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

Quote:
Originally Posted by ForSeTi View Post
Question for any metal techs out there

I'm building a Scarab Trimaran.
Working on the rudder atm, and it requires a SS Tube, 33,8mm OD, 6,35mm wall.
As a privat person, I cant get these dimensions in the length I need (I need like 1200mm, minimum amount I can buy is 6meters, which would be a bit costly)
Question now is, does a full 6061-T6 aluminium bar with dia 35mm be a good replacement for the SS bar?
The answer to the question is, No.

The SS item you describe is simply a piece of ordinary pipe, 1 inch Schedule 160 pipe 48 inches long, 316 stainless steel. Here in the US it's available routinely here...

McMaster-Carr

...for $235US for a 60 inch long piece, nothing to it.

I don't know how pipe is specified in metric using countries. If it's specified in inches, look for it in the above terms from industrial supply places. Or else ask McMaster-Carr above to ship you a piece, they're experienced at shipping worldwide. They can cut to your length, and ship that. And never mind all this baloney.
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Old 03-05-2015, 20:38   #50
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

Stumble-
Until the collapse of the USSR (world's primary source of titanium) it was a "strategic material" and you could pretty much only dream about it. So titanium "now" is dirt cheap by comparison. I understand the USSR actually made one (two?) nuclear sub with a titanium hull--even the US couldn't afford to do that, then or now.
But.
There are four primary titanium alloys used, you aren't pricing pure titanium, you need alloy quotes.
And titanium is a b|tch to machine, it eats machine tools the way good teak eats cheap blades. Which also means a lot of machinists hear the word "titanium" and run like vampires at a garlic fest.
And then you've got to find rod stock or tube stock, not just ingots. Unless you really want to generate lots of your own scrap. How many places compete for that market? In what volume? Ka-ching!


Nah, the stuff is still just wrapped in extra costs. If you think finding a "welding shop" that can simply do a good job on stainless tubing for a pulpit isn't easy...just try finding anyplace that deals in the titanium stock, even if you're planning to "just" bolt it in place.
Great stuff but like who was it said about yachts? If you have to ask the price, you can't afford it.
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Old 03-05-2015, 20:52   #51
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

BTW, Titanium is about 1/2 the weight of stainless, and virtually as strong.
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Old 04-05-2015, 05:10   #52
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

On my heavy displacement boat, SS rudder is full solid, say 1"3/4 or 5,5mm OD
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Old 04-05-2015, 08:59   #53
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

HelloSailor,

Off hand I can think of three places that I can get quality Titanium work done locally, and one U.S. Manufacturer targeting mass produced titanium parts. Having worked in the industry for two years I probably know a good bit more about it than most.

Any welder than can do decent stainless or aluminium welding can do titanium work as well, it just requires a backside argon shield. Fabrication is trickier due to its strength and kickback, but machining it's all that bad. Normal metal working tools work just fine, with lots of cutting oil (refined olive oil works best) and slow speeds.

The U.S. historical price on titanium was driven by poor US policy. Because it was a strategic metal the military could only buy it from US sources, and monopoly preventions were waived. So the major U.S. titanium supplier bought out all the rest, and ensured there was no other manufacturer to compete with them. Then they never reduced prices after better refining techniques took over the industry and costs plummeted.

Right now the cost of titanium has been in a downward spiral for years as usage grows and mills can ramp up production. Long term industry estimates predict this will continue for a number of years. And at least for US users it is happening pretty fast. right now the major cost driver isn't production it is in the distribution end. With suppliers charging 100 times their cost for a part (McMaster Carr is the biggest culprit).

But new suppliers are starting to stock titanium fasteners (Ace Hardware, Fastenal) which will help a lot in market penetration. Once people start seeing that it doesn't have to be expensive they will start demanding it elsewhere.

Just as an example, ronstan charges I think $75 for a lifeline stantion, Gurhauer charges $50, and Allied Titanium charges $60 for a titanium (G2) or $80 for G5.
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Old 04-05-2015, 12:16   #54
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

Just a quick FYI...switching to Imperial units McMaster Carr shows McMaster-Carr
4 feet of 1 1/2" 1/4" wall thickness SS tubing at $194.32 USD.
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