hi divergent thinkers. here’s a bonkers one (, and i’m throwing it out early; I haven’t really done any research, im hoping this catches the eye of someone with some experience, before I go out trying to acquire volumes of dangerous acid.)
I want to build some bikes using some absolutely mental, huge aero-profile 4130 tube (think 85x36mm).
BUT, I can only get it in 1.2mm wall… i’ve got some, it’s notably heavier than id like. I’d be stoked with 0.8-0.9mm happily.
has anyone had any success thinning thick wall tubing? Im thinking about the possibility of acid-etching it, though know basically nothing about this, is there any experience here?
I don’t think I want to start removing material by sanding/grinding/cutting etc. I suppose I could, but id really rather not.
Yeah that’s basically the idea. Man, race car guys are wild. It seems like they’re pretty concerned about the structural capacity of the bodies once it’s done.
I’ve been reading a bit about the etch eroding both different parts of the grain structure and maybe not eroding some alloying elements at the same rate/at all. Also about hydrogen embrittlement with 4130.
It’s sounding potentially, pretty sketch. I’ll leave this up incase anyone has experience with 4130 and I’ll keep reading.
Seems like chemical milling is the wording I’m looking for.
You’d be better off buying some 0.9 sheet and folding it over a wood buck to create your profile. In my opinion. That’s how I am planning on doing a wild TT project bike in the future.
At the 2019 NAHBS show Panasonic had a frame that they did just that with. I spoke with the engineer about it and he told me they ruined a number of frames before they figured out what needed to be done. With that said they also mentioned that the one they had was not for sale because of liability concerns.
I was also thinking about hydrogen embrittlement, but in this case the normalized 4130 is “probably” not hard enough for embrittlement to be a problem.
My worry was getting even erosion on the entire surface with no thin spots. I figure scouring the surface regularly could help, but I haven’t come up with a practical way to verify the tube wall is even afterward.
There is a company that will do .035” wall aero tubing. They are called AED metals. I got a quote on a tube that was 2.36” x .96” and it was about $220 for 6 feet of tube. Totally possible just expensive. They provided the quote along with an alternate option very quickly too. Might be worth checking out. www.aedmetals.com
that’s the size UNDER the one i’m after, which I also have on hand, its reasonably commonly available. the next size up (~86x36mm), the size Im looking for, isn’t available in 0.035". I don’t thing the stock round tube they presumably roll it from is even very common…
given the other factors, even erosion, potential embrittlement, capacity for ruining tubes/bikes etc. I think ill park this for a little bit, after an evening or two trawling google…
ill think about making a tube from sheet, and maybe press on with the heavy boy for now
Back in the day, you often had to use factory-spec bodyshells (hence “stock car”). But these were heavy as hell and then had to be fitted with a rollcage for safety. By thinning the factory metalwork you could save a ton of weight, then add the strength back in with the rollcage.
I love this approach, it’s got just the level of “sell the windscreen/teledega knights/because racecar/plastic windows” energy I try and channel… but the double duty of tubing in steel aero bikes (aero & structure) kindof complicates it’s application. thoughts of tube-length seam welds, or of not-steel aero bits really turn me off. Maybe with some practice, tube length seam welds wouldn’t be so scary…
I don’t think the forming of thin 4130 sheet would be a problem for me. And it WOULD give me more control over the profile…
Does the world need to suffer my having entire profile freedom for thinwall 4130 tubes at a reasonable weight?
