Roll Hoop on Drawing

I’d been poking around local tool stores for a while, looking for tubing benders. I’d found and purchased a 3-wheel tubing bender, but so far no mandrel-type benders. I need both types. Finally, someone suggested I try a shop that builds headers and exhaust systems, and bingo, success, not 100 meters from my daughter’s school. They have a huge floor-mounted motorized unit with all the necessary mandrels. Of course, on the same day, I found a shop selling mandrel-type benders but it appears I don’t need one now. So the header shop says, sure, they can build the rollover hoop, although I’d have to wait about 10 days as they’re booked solid until then. The price was right, however. Really right.

Rollover hoop in place on chassis jig table

They don’t have much (any?) experience working from drawings, unfortunately. When I went to pick up the two samples, the boss mentioned they’d bent the top section 15 degrees forward. I pointed out on the drawing, “You mean like here, where it says 10 degrees?” Oops. “We’ll fix that for you by tomorrow afternoon.” So I go back the next day and everything looks fine. I take them back to the shop and lay them out on the full-size drawing I’d given to the shop so they couldn’t possibly get it wrong, and, well, they’re not even the same as each other. One is about 15 mm too narrow. The other needed a half hour of work on my tubing bender to make it match the drawing, but we’re on our way!

I’d like to meet all the SCCA rules for Formula 1000, but sourcing the required tubing in Thailand is difficult. The prototype will have to be an adaptation of the US rules to fit tubing sizes and types available locally. Where SCCA rules require seamless or drawn-over-mandrel tubing for the roll cage, I’ll be using ERW (electrical resistance welded) tubes. I’ll also be modifying the required diameters and thicknesses a bit. That means this first prototype won’t be able to be homologated under SCCA rules for racing in the US, but realistically that wasn’t going to happen anyway. I visited a shop called “Boon Racing Pattaya” and talked to the owner about tubing. He said everyone in Thailand uses ERW for roll cages and recommended I visit Chinatown in Bangkok to buy any unusual sizes or types.