Yeti was a fun place to work. Skip, who works with me at FTW also worked at Yeti. Skip worked in the paint department so he knows some things I don’t.
I have seen a few rusty Yeti frames. Usually older ones. John and Linda lived at the beach and we rode the Malibu hills from time to time. When Chris and I started helping John he gave me a red FRO frame that was pretty rusty. We never imagined people would be collecting them. John came from a racing background and most racing machines are discarded, quite unceremoniously in favor of a new machine.
We love our old bikes don’t we? I sure love mine and this proud owner loves his.
I was a little intimidated by the project actually. I have a really amazing tube bending set-up but the yeti stays were something I never personally did. I drew pictures of them and mocked them into frames but that’s it. All the Bending at Yeti was done by an aircraft contractor in Burbank.
Bending 4130 in a small radius is very difficult. The mandrel penetration is critical and the tube must be coated with a high-pressure lubricant. I didn’t have the right mandrel so the whole process began with making a proper mandrel and heat treating it for durability.
It takes several bends to have one work properly. The tubes will either snap (mandrel too deep) or buckle (too shallow) but by the sixth or so try, it works. I pull a few more for good luck.
The actual stay tube is nearly 1M (3′) long before bending. There is limited access around the bending dies so each bends location must be planned. On the original tail, the beginning and ending of each bend must be marked and the amount of tube for each bend accurately calculated. On the left side, the bends at the lower tire and pedal are done first, then the tube flipped, end to end and the upper tire bend done. On the right side, the opposite sequence is used. Each bend has a correct measurement but before each bend, the tube must be rotated and over-bend estimated.
I have to turn the music off, stand on one foot and hop around with my eyes closed to visualize the parts in a 3-D state being formed. I am pretty good at “mental 3D modeling” but it’s still an effort.
I ended up only getting one set of these tubes done before simply running out of everything. Thankfully, they are perfect.
I re-used the original brake bosses and added vent holes.
Today (tomorrow), I am making some old forks.
I even used old-school parts to test fit everything!
Thats some incredible bending and even more impressive mental modeling. I know my bending ritual has me doing breathing exercises and jumping around and all that yields bends way less complicated than a loop tail. Nice Work!
Dear Frank,
Fab work. Looks the works!
Regarding the procedure. You mentioned you made your own mandrel and then heat treated it. It raises many questions. Can you show the mandrel? I am curious.
I find it cool that your make your own tools! Respect.
maybe you are taking orders to re-produce sherpas? Or ultimates?
That would be it…a ultimate 29er! Ha! Never mind my nonsense.
All the best from Germany,
Sarkis
Hi and thanks for your comment. The mandrel goes inside the tube when it’s being bent. Here is a link that covers the process.
http://www.allbend.com.au/images/bending-process/bend1.html
What I think at this point is that the 4130 tube is very inconsistent and the quality is generally poor. The owner of the Sherpa sent his own tube for the project and it was a good thing as it was easy to bend. I think he said it was Reynolds tube? Anyway, I couldn’t get good results from other material I had in stock.
I don’t know if I could do a early one-piece loop tail without some type of splice somewhere. I thought about using my own 29′r chain stays and tapering them to fit loop at the dropout sort of like the ARC chain stay. Then at some point I came to my senses and realized I shouldn’t do things like that.
The funny thing is, while at Yeti Bruce Gordon gave me some Rock and Road tires which were the first 29′r tires in my book. I could have invented the first 29 but I didn’t. I did build a bike with those tires but it had drop bars and not enough tire room. I also needed wider rims or much greater tire pressure than I was using.
Impressive bending frank. Came out great. Please do post up a picture when it’s complete.
Also, just looked at the original stays and it looks like one single piece for both sides. I imagine that starts out as a 6′ tube! I forgot what a nice piece of workmanship that was.
Respect to you as a craftsman, artist and my Yeti Ultimate’s Baby Daddy.
Love seeing the in process pics and looking forward to the final build pics.
Your comment re: forks. Please let us know if you get a wild hair to make and sell a few(fork and Stem). I have been gathering period correct parts for a full restore. I have night terrors associated with getting rid of my Accutrax fork and original stem when the first Manitou came out. Have been watching ebay for years to no avail.
Cheers from a fan
hotDAMN!
Frank, i knew it was a big job to undertake! Im sorry if it caused any sleepless nights!
BUT! Its made a YETI owner a very man..I cant wait for it to land on these shores then i can get to work on paint etc. P.S. please pencil me in for a 410 mm a-c Accu fork for this very frame.
Superb!
Happy man is what i meant to post
Nice!!!!
Greetings ;
Any pics of those old school forks you made…? tks