I've spent quite a while figuring out a reasonable technique for making nice curved tubes with butted tubing and I've had a reasonable amount of luck (after ruining plenty of fine American steel in the process of learning what not to do). If these items are popular I may offer some other options that I commonly use (curved 31.8mm seat tube for 27.2 post, curved 34.9 seat tube for 31.6 dropper post, curved 31.8 supertherm top/down tube, 19mm twin toptube/seatstays?)
Without further ado:
Please note: All bent tubes will exhibit some minor ovalization. It is up to the end user/builder to determine appropriate diameter/butting and miter/cope/join appropriately. There is no visible ripple/flaw at butts/butt transitions (transition from bent/straight on seat tubes is visible). Butts marked for builder's convenience on request.
-31.8mm diameter 9/6/9 double butted x 600mm. 90mm butts at each end. Curved 25mm over total 600mm length (approximately 1750mm radius). Appropriate for toptubes oriented either up or down, or for light-duty downtube. 4130 cromoly. Butt transitions are NOT visible after bending. $70
-Custom tube bending. Want something unusual? I can bend most sizes of commonly used bike frame tubing, both straightgauge and butted. Heat treated material will cost considerably more, but yes, I can do it. Contact me for a quote.