John Clay raised the problem of filling the voids that occur in the i nternal joints created by frame tubes and badly pressed steel lugs.
Framebuilders become well aware of the shortcomings of many of the frame co mponents that they have to use when constructing a frame; in particular the tolerances and accuracy of many pressed lugs leaves much to be desired. Th e void between the radiused internal angle of a lug is probably the biggest problem..or at least filling it with brazing material is, as John has high lighted.
I was around in the early days of the 1950s when frame components wer e in short supply, and the choice when building a frame was often either to adapt as best as possible old style and slack- angled cast lugs, or constr uct the frame without lugs..or use the bilaminated technique. But with the easing of the supply of raw materials along came supplies of pressed lugs, notably Franco-Suisse, Prugnat...in very short supply..and Oscar Egg Super Champion.
All these lugs suffered from the internal radius problems ie voids or empty pockets in the joint that did not exist in cast lugs. The way I was taught to overcome the problem was quite ingenious, but it made more work., but it was a technique that was easy to employ, in a sense, because we buil t the frames without the aid of jigs.
We started the brazing process by brazing the top head-lug to the top-tube, and by brazing the bottom head lug to the down tube. Note that the head tu be is not mentioned. We would braze these joints by applying the filler rod from inside the lug and drawing it through the joint and along the tube. T he void would then be over-filled. When cool the surplus braze material on the inside of the lug would be carefully filed to ensure that the void no longer existed and that the joint had a perfect mitred profile so that to all intents and purposes the inside of the lug was as accurate as a cast on e. Later on we bought an expanding reamer that gave more precise profiles a nd diameters. When we had filled these joints we carried out the same proce ss by attaching the seat lug to the other end of the top tube, backfilling the joint with braze material and then filing away the surplus Once the top-tube head-tube and down-tube were assembled and ready for braz ing we would carry out the process with silver solder that melted about 230 degrees lower, thereby ensuring that the braze material in the voids wou ld not be melted and the integrity of the joint not compromised. The s ame process was applied to the seat tube joint. As for the bottom bracket joints and chainstays, the brazing rod was applie d from the inside of the shell and sucked up the tubes. Back-filling any ra dii in the bracket was quite easy.
In later years and following training with the British Oxygen Company I bec ame much more proficient in controlling the movement of brazing spelter with the torch flame within a lugged joint and also outside on lugless f rames. I abandoned my early void-filling technique and became very ski lled at filling the voids by using an externally applied rod of thicker than normal diameter, say about 1/8", and a smaller than normal nozzle, usu ally a No1. With the much smaller flame I could almost stroke and coax th e slightly pastier filler rod into the voids, by controlling the heat and t he rate of flow of the braze material at the same time. As my tutor at the BOC always said...Always use the smallest nozzle possible. It may take a li ttle longer..but a craftsman with a lighted torch in his hand should neve r be in a hurry.
Hope this helps, John. Neither way gives rise to any real difficulties..it' s all a question of time..and practice...and control.
Norris Lockley....Settle UK