Hallett frames are built using lightweight steel tubes joined using the traditional methods of brazing, silver brazing (also known as silver soldering) and fillet brazing.
Brazing is the traditional, old-school technique used for joining steel cycle frame tubes. In a brazed joint, the filler metal has a lower melting point than the base metal and penetrates by capillary action the gap between the surfaces to be joined.
Also known as silver soldering, this process uses a costly silver-based filler rod with a lower melting range in order to reduce the temperature to which lightweight alloy steel tubes must be heated to complete the joint. Silver solder must be used when brazing stainless steel.
Fillet brazing (Top left pic)
Also referred to as braze-welding,
bronze-welding or ‘lugless’ construction, fillet brazing is the process of joining the frame tubes by feeding brazing rod into a molten pool that fills the angle between the two tubes.
Once the fillet has been laid, the filler metal is shaped and smoothed using files and abrasive cloth to leave curvaceous transitions between tubes. It is not only aesthetically pleasing but allows the frame builder complete freedom of choice over frame angles and tube diameters to be joined. It is also used in the making of bi-laminate lug work.
Fillet-brazed frame joints are light, strong and fatigue-resistant.
Lugs and lugwork (Middle pic)
Lugged and brazed frame construction is the traditional way of making a steel bicycle frame and is still popular today. Frame lugs are steel sleeves found at tube junctions. They are shaped to provide a gradual dissipation of stresses and to enhance the visual appeal of the completed machine.
Most lugs are cast in sizes and angles suitable for standard tube diameters and frame geometry. Although some manipulation is possible with steel
lugs, the builder is inevitably limited to a smaller range of angles and sizes than is possible with fillet brazing.
Bi-laminate (Top right pic)
This combines fillet brazing with the decorative, strengthening and stiffening effects of lugs.
Originally developed in response to material shortages after the second world war, it involves brazing profiled sleeves over the relevant frame tubes, which are then joined and finished as with fillet-brazing.
The technique offers the builder complete freedom not only over frame angles but, since the sleeves are cut by hand, over their shape.