Thursday, April 29, 2010

Rob's BiLam 29'er

The inspector has returned, and all she has to say is, "what the heck is this crap"?
Well, I'll explain. Rob sent along this picture of his lugged '92 Paramount and asked if I could build a modern lugged 29'er. Not an easy task considering the extreme angles that suspension corrected 29'ers present. On the upside, Rob's a pretty big guy and that helps make some of the angles less problematic.

I decided to go with a standard size seat tube, 28.6mm, externally butted at the top, and then a 31.8mm top tube and 35mm down tube. A set of double bend chain stays and Paragon chain stay mount disk dropouts finishes things off.

I spent a fair amount of time figuring out where to locate the bends and bumps when I built my 29'er last year, so I knew pretty well where to make my cutoffs and bumps for tire and chain ring clearance. I did have to do some work on the chain stay sockets of the bottom bracket shell. It's a road shell, so the sockets are not angled as much as you need. After some subtle persuasion, they came around.

I used some 4130 tubing to make the Bi-Lam lugs. First I mitered the end to match up with my geometry, then I drew my design on the tube and cut it out roughly with a hacksaw. Once I had a manageable sized stub, I tacked it onto the head tube where I could do the final shaping. Below is the head tube with the top and down tube "lugs" attached. I made the down tube lug a little extra long on the bottom to act as a gusset and the forked tangs should distribute the stress outward.

The tube set, lugs and chain stays all ready to be brazed.

A better shot of the bi-lam head and seat lugs.

Once it's finished the Inspector has to have a look! The cable guides are brazed onto the head lugs, reminiscent of Rob's Paramount.

The fillet brazed seat cluster with my custom bent seat stays and bridge.

Paragon dropouts. I'm really liking these!

A shot of all the curvy stays and bridges.

"I guess this one's OK"...



Mick Peel said...

absolutely beautiful work, I love it.

Anonymous said...

Like the Inspector, I'm just speechless.