Classic Lightweights UK
Claud Butler Bi-laminated FramesAuthor Martin Vincent
Claud Butler himself, never a man to understate the case when it came to promoting his own products, had this to say about bi-laminated frames:
The bi-laminated frame is 'The greatest advance in frame building technique since the evolution of the safety bicycle. 25 per cent stronger than the ordinary brazed joint, as proved by official NPL (National Physical Laboratory) tensile test. Enables me to build your frame to any desired angles (if practical) without lug pulling. Proved sound by practical demonstration on the roads and tracks of the World, including all post-war World's Championships and Olympic Games series. THIS IS THE TYPE OF FRAME CONSTRUCTION WHICH I RECOMMEND.'
Thus the CB brochure for 1951 gushes praise for the bi-laminated principle of frame construction. It may be over-stating the case when he describes it as the greatest advance in frame building technique since the evolution of the safety bicycle, but there is little doubt that the end result is a frame joint that is stronger and with less flex than either a plain fillet-brazed joint or a brazed lug joint.
1951 Claud Butler Olympic Sprint with long spearpoint bi-laminated lugs - a classic track frame of the era
What does Bi-laminated mean?
It is basically a system whereby a frame is constructed using reinforcing sleeves that are brazed to the ends of each of the tubes. The tubes are then mitred and sif-bronze welded (fillet brazed) to create the frame. The resultant structure benefits from a reinforced joint area. The sleeves are shaped not only to give a decorative appearance in the manner of conventional lugs but also to remove any sudden change in section which would produce stress raisers.
The bi-lam unclothed. The sleeve strengthens the tube at the joint area while fillet brazing produces a neat and strong jointThe Advantages
(Images Hilary Stone)
In addition to the obvious structural advantages of having more material at the area around each joint, this type of construction allows any angles and any size frame tubes to by used, within reason. Oversize top tubes were often selected to further improve resistance to twist or 'whip'. So, in practice, does it result in a superior frame? In my experience of riding a 1955 Avant Coureur Spécial, the answer is yes. It is notably steady with reassuringly consistent steering, yet it is also lively and retains a resilient ride. In terms of stability it bears comparison with a Cantiflex-tubed Bates or the more modern Colnago Master, both of which feature specially profiled frame tubes to produce a stiffer frame.
This is what Cycling Weekly's Nimrod had to say after an extensive three-month trial of an early pre-production Avant Coureur in 1947:
'I would have no hesitation in recommending it to the mass start rider, the time triallist or any other lightweight connoisseur. The liveliness of the machine and the steadiness of the steering at all times and on even the worst road surfaces was remarkable, and to back up the manufacturer's confident assertion that 'whip' is eliminated completely, I can say that never at any time did I feel the slightest sign of this unpleasant tendency.'
The bi-laminated principle does indeed deliver the goods.
Before the Bi-lam.
The bi-laminated frame principle was a development of the bronze-welded frame, now commonly known as fillet-brazed. It seems that the technique of joining lightweight frame tubes by creating a fillet of braze around the tube joints using SIF-bronze welding became well established in France by the mid 1930s. At this time, the organisers of the Tour de France race stipulated that all competitors had to use the same type of bicycle. The chosen design was bronze welded, a relatively new process for very thin-walled cycle frame tubing.
Left: The CB Jubilee frame is bronze welded, a technique used since the 1930s. Bi-laminating was a development of that process.
The T de F machines would have been displayed at the Paris cycle show and it is certain that the likes of Claud Butler, Sandy Holdsworth and Harry Rensch would have taken an interest when they visited the show. Sure enough, these makers began experimenting with 'welded' frames shortly afterwards and these were in production pre-WW2. The bronze-welded frame really came to prominence soon after the war, when lug sets were sometimes in limited supply due to the steel shortages. Adding bi-laminates to enhance the integrity of the joint was a natural development of the fillet-brazed frame.
It is interesting to note that today's fillet-brazed frames are generally more expensive than lugged frames because it is a highly skilled process and skilled labour is not cheap. Immediately after the war, however, there was no shortage of skilled labour and labour was cheap, so fillet-brazed frames were generally less expensive than their lugged equivalents.
THE CLAUD BUTLER BI-LAM DESIGNS
Partial-bi-lam Axe Head
This is probably the first of the CB bi-lams that was labelled as such and it is a variation of the classic CB Axe Head lug design. It consists of axe head design sleeves or bi-laminations over the three main frame tubes only. The bi-lams are absent from the head tube itself. This was used in 1947 for a pre-production Avant Coureur tested by Nimrod in Cycling and described in the October 8th edition as 'introducing a new method of frame construction, the CB patented 'Bi-laminated' process.'
1949 Sport Anglais with partial bi-laminated Axe Heads.The pictures clearly show the pre-poduction Avant Coureur frame with these partial bi-lams, but whether these were also used on the first production machines is not known. Despite the 1947 Cycling feature, the Avant Coureur model was absent from the 1948 brochure so it is not known whether it had the partial bi-lams on its introduction that year. What we do know is that for the 1949 model year it had the full axe head bi-lams which are described as an 'improved version of the CB Bi-laminated' principle. The partial bi-lams, however, were a feature of the 1949 Sport Anglais model and also for the Deluxe Tourer of that year.
The same design was used for the pre-production Avant Coureur
It has been reported that a CB frame with partial bi-laminated construction was made as early as 1940, although it is probable that any such frames were one-offs or prototypes as there is no mention of this type of construction in sales brochures of the period. It would seem that the partial bi-lam design was not used after about 1950.
The axe head design dates way back to the late 1930s with the Anglo Continental model, although this was a lugged frame. The same attractive and distinctive design was introduced using the bi-laminated principle on the Avant Coureur model from the 1948 model year (it is thought) until 1951, when frames with this design became known as the New Allrounder. Meanwhile, the top of the range Avant Coureur model became the Avant Coureur Spécial for 1951, with entirely different long spearpoint bi-lams (see below). The Axe Head design continued with the New Allrounder frame until the closure of the Clapham works in October 1956. The Axe Head bi-lams were also a feature of the Olympic Path model of 1949.
Classic Axe Head bi-lams shown on a '53 New Allrounder.
Initially, this design was reserved for the Olympic Path and Avant Coureur
De Luxe Long Spearpoint
This type of bi-lam was used initially for certain CB path or track models from about 1950, presumably because it resulted in particularly strong joints. The design was also taken up for the new Avant Coureur Spécial. Long spearpoint bi-lams were used for the following models:
1951 Championnat d'Olympique (track)
1951-52 Avant Coureur Spécial
1951-55 Olympic Sprint (track)
The elegant Long Spearpoint bi-lams were popular with CB track riders in the early '50s.
The design was adopted for the Avant Coureur Spécial for a short period
This was a feature of the following models:
1953 A/C 53
1954-55 Avant Coureur Spécial
1955-6 Avant Coureur
Short Spearpoint bi-lams on the author's 1955 Avant Coureur Spécial.
Like many CB bi-lam frames, this one has an oversize top tube
A striking feature of the new for 1953 de-luxe short spearpoint bi-laminations is the resemblence to the very much in-vogue Nervex Professional lugset. However, it is only in the head tube profile where this resemblence exists.
POPULAR CLAUD BUTLER MODELS FEATURING BI-LAMINATED FRAMES
Identifying the different frame models can be somewhat daunting because CB had a tendency to use different names for the same bi-lam design. Therefore, It helps to know the year of manufacture. Fortunately, all bi-laminated frames produced in the 1950s have the year and month of manufacture stamped on the bottom bracket alongside the serial number. For example, the number 549 was a frame produced in September 1954. If a CB bi-lam frame has no date marking, then it must be pre-1950. No bi-laminated frames were produced after the Clapham works closed in late 1956, when the production of 'real' Claud Butler frames and cycles ceased. Here is some additional information on the most popular bi-lam models:
The Avant Coureur, A/C 53 and Avant Coureur Spécial
The Avant Coureur was a top of the range model and was produced with Reynolds 531 (or Kromo) butted tubing throughout and with 74/72 angles. Of course, any angles could be specified to special order, and it was not uncommon for the larger frame sizes to be produced with an oversized (1 1/8in) top tube to add further rigidity. The Avant Coureur models featured a special sleeved seat cluster with integral clamp and semi-wrapover seat stays. However, the other bi-laminated (and fillet brazed) models usually lacked the reinforcement at the seat tube and therefore required a separate seatpin clip. But there are exceptions. Certainly some New Allrounders were produced with the Avant Coureur style seat cluster, although whether this was due to supply shortages, special customer orders, or variations for a certain model year is not known.
The Avant Coureur was produced from late 1947 to late 1950 with Axe Head bi-lams
For the 1952 model year it had 'De Luxe' Long Spearpoint bi-lams and it was called the Avant Coureur Spécial
For the 1953 model year the bi-lams were changed to Short Spearpoint type. This was called the A/C 53 for 1953 only.
The name reverted to Avant Coureur Spécial from 1954. However, the final catalogue CB produced in November 1955 lists this same model as the Avant Coureur - the 'Spécial' was dropped once again.
No wonder there is confusion in defining this model.
(Click on image for larger version - possibly second click to undo screen size restriction)
© 2012 Classic Lightweights