OK, I'm really going to show my comploete ignorance here! I'm in the process of trying to turn a folding bike (an old Raligh 20) into a folding short wheel base folding recumbent.
Most everything is going OK with the planning and building but at this point I'm about to design and build a forward boom to support the bottom bracket. I have the 4130 steel for the boom itself, but I don't know a thing about bottom brackets!
My problem is what size of tubing does one use for the bottom bracket itself, and what length? Or does it all vary depending on what kind of a BB I plan to use?
I can TIG weld OK and have no problem with the actual frame construction itself, but am really new to the actual mechanics and size to build the bottom bracket. I plan on using the existing BB as a mid chain vaguely like the Cannondale Bent 2 and a few others. This should help to allow it to fold.
But I know nothing about BB's themselves, or can I pick up one on E-bay and weld it to the boom?
Thanks for any information you can give an ignorant newbie like me! Meey Xmas
It sounds like what you need is available from www.paragonmachineworks.com they also sell through the UBI store- www.bikeschool.com, I think.
Paragon makes some of the best bb shells out there and they are only about $5 a piece!
Unless you have a nice lathe at your disposal, the tooling costs to make your own would be prohibitive.