[CR]Re: A new "vintage" frame design question (and a vintage brazing Q)

(Example: Racing:Jean Robic)

Date: Wed, 17 Sep 2008 10:50:40 -0700 (PDT)
From: "John Clay" <jmedclay@yahoo.com>
To: Classic Rendezvous <classicrendezvous@bikelist.org>
Subject: [CR]Re: A new "vintage" frame design question (and a vintage brazing Q)

Reading about Norman Taylor's fillet brazing technique got me stoked. Thanks Norris, for all of the info you shared to the list. It reminded me of this - I mentioned building a frame around a particular tire and some old components a couple of years ago. While in the literal sense it isn't "timeline compliant", it certainly is in every other way. Photos here:

http://www.flickr.com/photos/21624415@N04/

650B x 32 Cypres NOS Superbe brakes NOS Cyclone changers (Thank You, Dale!) 8/5/8 Nivacrom, modestly thin walled stays (.8 I think) pressed lugs, IC BB, all with brass ~40mm trail Misc. other old stuff hanging around.

I added fork-leg-loops for wires from a future gen-hub but in retrospect should have added a bottle generator boss instead; night time use is infrequent and a couple of hours duration. Existing bottle generator is the cost/benefit ratio winner for this bike.

It rides and handles wonderfully. Pretty neutral steering with/without modest front load, comfortable. Need to address the junky gear ratios.

************************************************************************

I don't know if the older guys did this, but I am on a quest to flow pressed lugs so that when cut apart, there is 1) no void in the lug crotch area and 2) a complete fillet on the ID of the intersecting tube. The void issue is most challenging, a complete ID fillet much less so. It's not about basic joint strength either; after cutting some old frames apart and talking to others who have done so.....well, let's just say I'm comfortable there. It's about making the joints closer to perfect, in areas that will never be seen. Getting a consistant full flood of brass in the lug crotch void, particularly the acute angle one, is elusive, very difficult; the goverening physics are working against it. I am messing with flowing from the top of the crotch (not so good a fill), both flanks to join in the middle (better, sort of back-fill it), one flank across to the other (better still), more torch dwell over the void area (good for the fillet at that location but doesn't help the void it seems), and some other variations. Flowing across the miter is no problem but getting brass to work against the surface tension in the void area is a bear. All the void surfaces are tinned (upon dissection) and the void is encapsulated. But, there is always at least some void (or flux filled) area. If anyone has wisdom or other ideas please let me know. The one thing I haven't tried, and which will probably work (but offends me a little), is drilling a small hole at the lug crotch, and flowing brass directly into the void. Anybody know of this being done in the past? I'll soon try it.

Thanks,
John Clay
Tallahassee, Florida
USA