[CR]Lugged frames v. fillet brazed..now v. bronze-welded

(Example: Framebuilding:Tubing)

From: "Norris Lockley" <norris@norrislockley.wanadoo.co.uk>
To: <Classicrendezvous@bikelist.org>
Date: Sat, 3 Dec 2005 01:45:09 -0000
Subject: [CR]Lugged frames v. fillet brazed..now v. bronze-welded

Wow! What have I been missing over the last few days since my computer went down...yet again! Such contraversy on a number of issues on the List!

Perhaps it's just that I feel liberated having just triumphed in rubbishing a £4.3 million law suite against me.. no..nothing to do with bikes..and had the case declared "Null", that I feel I need to keep the adrenalin pumping by throwing my opinion into this debate about lugless v. fillet brazed frames.

I think that there really is an empirical answer to this debate..just the individual's value judgements, so I don't want to enter that forum.

The aspect of this issue that vexes me, perplexes me, enrages me..is that I am pretty certain that there is no such thing as a "fillet-brazed" frame. There are lugged frames that are normally brazed ( "normally" because some recent ones have been bonded), and then there are lugless frames that are welded, either by torch, arc, TIG, MIG, or other means as pointed out by Michael Butler ie the Daytons and the Royal Enfields. No doubt there are other means of welding frames. Welding does not always mean fusing the tubes, with a rod or electrode of the same metal as the parent metal of the tube, although I do have pre WW11 Alcyons, Peugeots and Automotos that are fusion welded in this way. The vast majority of welded frames are built using some form of brass/bronze rod, that melts at a lower temperature than the parent metal of the tubes. However all hand-welded frames have one thing in common, they all have fillets/beads/cordons of weld metal around the joints. These can be very small or built up with several passes to create a sculptural appearance, almost, at times, resembling a casting.They can be things of beauty, they can be crass and ill-formed..but all welding leaves some form of fillet or bead.

On the other hand brazing leaves no such fillet or bead. A fillet could not be created or result from the brazing process.. Brazing is the process of drawing an extremely thin film of molten filler metal through an equally fine gap between pieces of metal to be joined. The flow of the metal is the result of a process called capillary flow...the same process that draws ink out of a fountain pen knib in the course of writing. IMHO and experience it is impossible to both create a fillet and braze in the same operation. The characteristics of the rods used in the two processes are in fact different. Brazings rods need to be more "runny" and fluid, while welding rods need to be more "sticky"and pasty.

The finest brazed framed I have ever seen was in fact produced in France, in the mid-90s, and was made from 6068 aluminium alloy. At no time during the brazing process was a torch present nor an electric current. The whole frame was assembled by mechanical means ie very fine pins, and "brazed" by immersion in a vat of vicious-looking purple liquid, containing a heated lithium solution. The braze material was placed on the joints as a paste prior to immersion. The whole frame expanded uniformly in the vat/tank thereby eliminating ALL distortion, and the braze material flowed uniformly within a liquidous band of 3 degrees of the flow temperature. X-ray and other tests showed the brazed joints to be 99.8% homogeneous. The finished frame needed no post-brazing tracking or checking - alignment was 100% perfect. The process is known as "salt-bath brazing" When I enquired of the welding rod manufacturer Castolin-Eutectic what this process was normally used for , the reply was "heat exchangers for space rockets and the like". Having pinned my colours to this particular mast, I need to admit that the term used in England, bronze-welding, does not use many forms of bronze in most cases, but varing types of silicon or nickel brass. The other misconception to remove is that almost all metals can be brazed, including aluminium, and also welded.It's just the filler rods that vary..and the fluxes.

I feel better for that.

Norris Lockley...Settle, Uk