Simple Soldering.
—Scrupulous cleanliness in everything connected with the process of soldering is essential to success. The ordinary procedure in making a joint is to clean the surfaces first by filing or scraping with a scraper or a knife or a plumber’s shave-hook ([Fig. 17]). In some cases, dirty metal is cleansed with dilute hydrochloric acid. With or without preliminary heating of the work, flux is then applied to the joint, and the heated bit is held in one hand and a stick of solder in the other, and the stick drawn along the joint while the bit touches it (or “drops” of solder may be transferred to the work by means of the bit). This will cause a line of molten solder to run, and some skill and care are necessary to get just the right amount of solder without wasting it and allowing it to spread in a lumpy fashion beyond the necessary area. The bit is next worked up and down the joint to spread the solder, and by the transmitted heat to make it thoroughly penetrate the joint. This is an outline of the process, and there is a number of points requiring special instruction or a few words of caution.
Fig. 17.—Shave-hook
Note that the work must be filed, scraped, or otherwise mechanically cleaned, and then chemically cleaned by coating with the flux just where the soldering is required. In heating the copper bit do not let it reach even a dull red heat. Lightly dip it into the flux to clean the point; then, with a small button or blob of solder resting on the work, place the bit momentarily upon it to cause the solder to flow, and draw the bit where the solder is required.
Many beginners try to draw along the solder with an insufficiently heated bit. The result is a series of lumps—“putting it on with a trowel,” as it is sometimes termed. A good joint cannot be made this way, however much solder may be used.
Some beginners fly to the other extreme, and try to make a neat job with a red-hot bit, which results in the solder assuming a sandy appearance and in the work being discoloured.
Others try to solder uphill—that is, they hold or place the work in such a way as to cause the solder to flow away from where it is required. The correct method is to solder downhill by tilting or inclining the work, so that the solder will always collect around and travel with the point of the bit. This, besides facilitating the work, makes a strong joint, and imparts a clean and neat appearance to the job.
Figs. 18 and 19.—Incorrect and Correct Methods of Holding Bit
A common mistake is to hold the bit in a cramped and awkward way, as in [Fig. 18], the hand being twisted under the handle, the thumb being brought to the top, and the elbow forced to the side. The correct positions of arm and fingers are shown in [Fig. 19]; the elbow is held well out from the body, and the thumb is placed directly under the handle of the bit, forming a fulcrum over which the bit may be slightly raised or depressed at will. This is all-important when soldering very fusible metals such as pewter, tin, etc., on which the weight of the copper bit should never be allowed to rest, as otherwise a hole will suddenly be made in the work. The whole weight of the bit should be supported and balanced on the thumb by the downward pressure of that part of the hand close to the little finger. The worker should not for a moment lose control of the copper bit, and control is always assured when the thumb is underneath the handle.
There is but little strength in a butt joint with the edges of the metal only just touching—that is, without a lap; to take the example of a small cylinder, the body seam should have at least a 1⁄4-in. lap. [Fig. 20] represents an example of internal grooved seam soldering, which may be executed in the following way:—After applying the flux, place a small button of solder inside the cylinder on the seam, rest the bit momentarily on the solder to melt it, and then draw it gently along the seam. The cylinder should be slightly tilted to allow of the solder travelling with the point of the bit. The hand should avoid touching any part of the work that comes directly into contact with the copper bit, as otherwise the hand would be badly burned.
Fig. 20.—Soldering Internal Grooved Seam
Fig. 21.—Soldering on Can Bottom Internally
The method of internally soldering the bottom on a canister, etc., is shown in [Fig. 21]. The bottom is held in position by gently pressing it against (but not placing it on) the bench during the soldering process, while the tilt of the canister and the position of the bit cause the solder to travel with the bit.
In soldering all such articles, the soldering should be done with one sweep of the bit, the left hand meanwhile making the necessary revolution. This saves time and solder, and avoids the unsightly appearance of a series of starts and stops.
In work of a larger and more substantial nature, as, for example, galvanised or tinned iron work, the bottom of the article is first “knocked up,” and then soldered internally. [Fig. 21] represents an example of internal soldering where the whole weight of the bit is shown resting on the molten solder inside; this provides the local heat required to “sweat” the solder into the four thicknesses of metal which constitute the bottom seam; and for this work the bottoming bit shown in [Fig. 3] is often used. Pewter, lead, zinc and tin—the latter should not be confused with tinplate—do not require sweating, on account of their low fusibility, and any attempt even to solder them with a very hot bit will probably end disastrously.
Fig. 22.—Soldering Can Externally
[Fig. 22] shows an example of external seam soldering. The method there shown is invariably adopted for simple lap seams, although grooved seams are similarly soldered. A grooved seam, however, should preferably be soldered internally. The position of the worker’s elbow and thumb should be noted, as should also the tilt of the cylinder (more pronounced in this case than the other) in order to secure the downflow of the solder.
Sweating has already been mentioned. It should be said that one of the easiest ways in which a beginner may make a reliable joint is to prepare both faces of the joint by fluxing and covering with a thin film of solder, and then pressing the two parts together with the hot bit until the top part “floats” and then settles down. The advantage of this way is that one can be sure of perfect application of the solder to the joint faces, since each is dealt with first and thoroughly coated, with no faulty patches. Sweating is also done in the flame of a bunsen burner or blowpipe, as explained later.