WORKING DRAWING DROP FRAME MODEL. ([See Page 52].)
What is known as “brazing spelter” is really a misnomer, and should be called brazing solder. Spelter is the crude product from which refined zinc results. Brazing solder is a combination of copper and spelter first cast into slabs or ingots, then placed into large mortars and pounded by a heavy pestle by hand, and, strange to say, that in all our recent developments in metal work no method can be found to supersede this method of manufacture, as this is the original method of making it.
There are altogether about eight grades of brazing solder, ranging from what is known as the coarse long grain to extra fine grain.
The first result of the pounding operation is the coarse long grain which comes out almost in shreds; by further pounding the shreds are produced, and the result is the fine long grain. From this operation comes the rough grain, the first being coarse long grain, the next medium, then fine and finally extra fine. The proportion of extra fine long grain to the other coarser grades or varieties is only about ten per cent. of the total, consequently making the latter grade the highest in price. The various grades are separated by sifting through a sieve. The running qualities of this solder are affected by the larger or smaller proportion of copper used in the composition. The more copper used the more heat required to melt it, the reverse being the case where more spelter than copper is used.
On bicycle frame work where the surface is largely exposed, the coarse varieties can be successfully used, but for the fine work where little heat can be used, and where the tubing is of extremely light gauge the extra fine grade, which is known also as the quick running solder, gives the best results.
Wire spelter, which comes in coils, has become very popular on account of its lessened cost, its cleanliness, and also because it is not so wasteful as loose spelter, and can be conveyed directly into the joint by the operator as soon as it has reached the melting point.
