Article in Wall Street Journal on new KRGT-1 motorcycle mentions this about the fuel tank:
Aluminum Shavings | Each 5-gallon fuel tank (18 pounds) is milled out of a 534-pound block
of billet aluminum in a process that takes 66 hours.
I guess that is one of the reasons the bike costs $78,000.
Is…there a benefit to milling away 516 lbs of aluminum as opposed to, I dunno, casting, welding or any other seemingly more sensible approach to manufacturing?
No. The same design with less weight could be achieved with a mold and hydraulic expansion. This is just a case of more money than brains…
It could allow for some interesting customizations though. 
Yes, If you mill something the structure of the Metal is not changed. Casting causes the metal structure to fuse which may not be as strong. Guess that’s why they choose 516 lbs block of Aluminum the center would be the most compressed structure. I think it’s a bit over engineered
The fact that the structure of the metal is not changed is why you do not use milling to make wheels. Forgings or, yes, (depending on the technique) castings are far more suitable. I submit that if you wanted to make the gasoline tank the best structural member it could be, you would forge it.
It’s a dickwag. “Look at me, I have so much money that I machined a gas tank out of a ridiculously expensive piece of metal”
Structure may have been a poor choice of words but where talking the same thing pretty much. Forging causes the metal molecules to press together. He is getting almost the same concept without a forge letting the outside weight of the metal provide the pressure. Guess he has to justify 78k
An excellent counter to this would be to make one out of paper machet (sp?) and some sort of glue that doesn’t dissolve in gasoline.
“$10 gas tank made from paper”.
— Zach
Papier mâché. Look, ma, my French classes finally paid off! Too bad my keyboard doesn’t have a compose key, so I had to cheat with the accents.
In that case, they should have made it from a solid block of Titanium.
“Hey look, my motorcycle cost as much as a Lamborghini!”
As long as it’s not used as a structural member, that would be fine. In the 19th century, lacquered paper (an original composite material!) was used for canoes, coffins, and observatory domes. It was the material Jules Verne used for the “aeronef” of Robur the Conqueror.
If they don’t expect to make very many of these, it’s cheaper in the long run to hog them out then to get the casting tooling made. And the early prototypes would still likely be hogged out as a precursor to the casting to prove out the design. AND … I believe there are only a couple North American casting foundries capable of casting something that size in an aircraft-quality casting. Last I checked, lead time was over 32 weeks, and that’s after the tooling exists.
I guess I’ve just watched too much American Chopper, where they’ll cut and weld together beautiful gas tanks in a couple hours and a few sheets of metal. XD