Originally Posted by
MassiveD
Is there a design you are copying in Ti? Ti is an interesting, and high tech metal, but not the sure fire solution. It is twice as heavy a Al, and 2/3rd as strong as steel. So you can make some stuff for which al is too soft, and steel is too heavy. On the other hand. It is flexy, and can end up providing less stiffness for a given weight that al would at far lower cost.
One interesting structure is the Bike Friday suspension boom. It is a little controversial due to concerns about fatigue, but it goes to show an application where Ti's flexibility is in play. So think carefully of what kind of characteristics you want from this thing, and whether Ti is the solution, which if you are copying some existent product, should be easy to resolve. But Ti isn't a magic bullet.
One other material is carbon fiber. Since it doesn't require welding, it is relatively easy for people to work with, and these days fairly cheap. It can be difficult to build light since very little goes a long way for stiffness, but the structure can turn out understructured in places. It can take one or two tries to get a working proto, but it is a home building option.
The only equipment made of titanium that I know of are wheelchair frames some bits and pieces, and fore-arm crutches. The wheelchair guys are very specialized and bend each tube for each specific client. Each chair built by hand, much like a bike. They have some master TIG welders, but won't branch out from wheelchairs.
I agree, it is very interesting. My industry s used T-6000 and T-7000 heat treated and hydroformed aluminum alloy to try to match the strength to weight ratio of titanium. It has been only partially successful. I have seen some hydroformed heat treated aluminum alloy frames fail. This industry use to use 4130 chrome moly but it has been largely abandon. Aluminum may be lighter by volume, but for a thin walled tube, it hasn't matched the durability and lightness of titanium. I would love to see some of the really thin walled alloy steel be used in adaptive equipment, but the industry lags behind bicycles and ties its own hands with the viscous cycle between funding agencies, manufacturers and suppliers. I think the higher end gait trainers are made of something below T-6000 aluminum. If I cannot find someone to take on a custom project like this, I would like to explore using ultra-thin walled alloy steel and try it myself, but my gut feeling is that I would not achieve the lightness of titanium tubing there. I personally would not know where to begin with carbon fiber, although I built some surfboards as a kid. Thanks for your input. It is helpful