Silver solder Posts

David Mercer – Mercer Bikes, Cape Town, South Africa

David Mercer – Mercer Bikes, Cape Town, South Africa

I met David Mercer at the Bespoke Bike Show in London in April 2014. I was impressed with the bicycle he had brought to the show, a touring bike he called the Monkey King. It could definitely be described as multipurpose, with a lot of hand made details including custom made stainless racks. David is a Vet by training and now splits his time between working as a Vet and building custom bikes, racks and tools. He kindly agreed to answer some questions about his workshop techniques which interested me:

Brass, Silver and Flux

Brass, Silver and Flux

Thus far I have used the following filler rods and fluxes on my projects and suspect they are the most widely used:

BRASS:

SIF 101, relatively low melting point brass rods in variety of diameters, 1.5, 2, 2.5 and 3mm. For lugs and braze-ons (1.5mm) and Fillet brazing (larger diameters). SIF do their own fluxes but I favour the Cycle Design Low Fuming Bronze which I find much easier to clean off and generally better in use.
See Cycle Design Products at: http://cycledesignusa.com/wp/

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SIF No 2, slightly higher melting point and harder result. I have used this for small fillets but its main benefit is it can be used to braze stainless steel. Unfortunately in this case it needs to be used with the specific flux viz. Tool Tip/Braze Stainless flux which does not seem to melt as well as other fluxes. That said I have used it to braze a lugged stainless fork crown with no problems. Mine has come as a crystalline substance like sugar and I find grinding it to a powder with a pestle and mortar or hitting it with a hammer in a plastic bag enables mixing a much smoother paste more quickly as otherwise it takes an age to mix. It takes up water only gradually and therefore if used too quickly will harden so I even found leaving it overnight to ensure full water take up was useful. Equally when heated it dries rapidly and has a habit of dropping off the work. I spoke to someone who had used it extensively and he found it was effective used dry by warming the tubes and covering them in dry flux and also warming the rods and constantly dipping them, the heat enabling the flux to adhere.

SILVER:

SIF No 43, 55% silver solder in 1.5mm rods, 0.5 metre lengths, for lugs and braze-ons.

CYCLE DESIGN FILLET PRO, Silver solder for fillet “brazing”, also useful for filling gaps such as slotted dropouts. 2.35mm diameter sold in coils by the troy ounce. 1 troy ounce = 31.1grams, which equates to about 0.78 metres of fillet pro 2.35mm and a little over 1.8 metres of the 1.6mm diameter.
I use both the above solders with the Cycle Design Stainless Light flux which is very smooth to apply and washes off very easily compared to other fluxes I have used. Like all fluxes it come with health warnings about toxicity and it is the one flux I have used that I would wear an appropriate mask for when fillet brazing because in this situation you use quite a lot of flux and hence a lot of fumes are generated which are pretty acrid. Using it with lugs does not generate as much fume.

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