Chapter 12

 

Chapter 12

Starting the Building: Glueing, soldering, etc.

WHEN we start building model aeroplanes, one of the first things we require is a smooth, flat board to work on. The ideal is a fairly large drawing board, but a good pastry board makes an excellent substitute, and a piece of plywood about 1/2 in. thick is also very good. We also want some greaseproof paper to put over our drawings to prevent the work sticking, and some pins to hold the parts in place. Pins known as French pins have large heads, and are the easiest to deal with.

Before going on with the construction, here are a few notes about glues, or cements, as they are sometimes called.

Glues such as Seccotine and Croid are useful for hardwoods like spruce and birch, and are perhaps the most useful for these. Durofix is suitable for hardwoods, and very good for balsa. It has the added advantage of being waterproof. There are also a number of quick-drying glues for balsa that are also waterproof. Seccotine and Croid may be used for balsa, and there is a range of LePage's glues for various purposes. For sticking the paper or silk covering on the model, a photo-mounting paste like Grip-fix or Bond-fix is best. Quick-drying glues are indispensable for carrying out repairs on the flying-field, as it is often possible to stick two pieces together by holding them in place for about half a minute.

Soldering is a job that is practically indispensable where really good models are concerned, and lots of people seem to find difficulty with it, so perhaps a few notes will not be out of place.

Cleanliness is probably the most important thing, and there is an old saying that is very true, that a job well prepared is half done. The parts to be soldered must be perfectly clean, first using a file or emery cloth and then using a flux to chemically clean it.

There are two well-known makes of flux - Fluxite and Baker's. Fluxite is a paste that is useful and convenient for brass, but when it comes to steel Baker's seems more successful, especially with a novice. Baker's make the well-known soldering fluid, which is specially recommended for steel, and also soldering paste, which is very good for either steel or brass. This does not mean that the soldering fluid will-not do for brass; it is in fact excellent, but needs more complete washing away afterwards.

The soldering " iron " is really made of copper, and must be " tinned " at the tip. To do this, file the tip bright and smooth, and heat the " iron," preferably in a gas flame or a clean fire (the red part) until it is just hot enough to melt a piece of solder on the clean tip. What is known by ironmongers as " blowpipe " solder is the easiest to use, as it is in sticks about 1/8 in. wide. Dip the end of the solder in the flux and hold it in a clean tin lid, or on a piece of tin, and melt off a spot or two with the tip of the " iron." Then rub the tip in the solder until it is coated with solder or " tinned." If the tip has been cleaned well, and the solder does not run freely and stick on nicely, although it is running, dip the stick of solder in the flux, and put a spot on the tip of the " iron." If this does not do the trick, the iron is most likely too hot.

Avoid getting the iron too hot, as it takes the tinning off; have it just hot enough to run the solder freely. It takes a little practice to get used to this. If the iron does get too hot, the only thing to do is to plunge it immediately into cold water, and start tinning all over again. The iron must always be kept well tinned, and if the tip seems hard when you file it, get it hot and plunge it into cold water. Never dip the iron into the flux, or in a short time you will find the flux eating into the iron, just behind the tinning.

Tinning the parts to be soldered is also a good idea, but is not always necessary. To tin them, clean with a file or emery cloth and smear with flux. Rub with a hot tinned iron, and add a little more solder if necessary, till there is a thin coating all over. Wipe away the surplus with a piece of rag while it is still running. The tinned parts are smeared with flux, held together and touched with a spot of solder on the tip of the iron. Hold the iron there just long enough to run the solder where required. If the parts are large you may have to add a little more solder. When finished, clean away all flux with a damp rag, preferably while the job is still warm.

Fig.21Fig.21

Sometimes, when the parts to be soldered are large, they are " sweated." This is done by putting on a thin coat of solder (tinning) where the joint is to be made, smearing with flux, and holding them together in a flame till the solder melts. The flame of a methylated spirit lamp or bunsen burner is the sort to use. Now a warning. Be very careful not to drop hot spots of solder on the carpet or table-cloth, or you will have the head of the household running you round with the rolling pin !

Something else useful to know is how to make drills that we can use for making holes in brass for gearboxes, parts of undercarriages, etc. It is, like a good many other things, easy when you know how. Very often when we want to drill a hole for a 14 or 18 s.w.g. propeller shaft we have no drill, but a piece of wire of that gauge can be used to make a drill. All we have to do is to file or grind the end to the shape shown in Fig. 21.

We grind the two flats on the sides first to make it something like a screwdriver, and then point it. Note carefully how this pointing is done. It forms two V-shaped flats that can be seen in the end and side views. In the side view, that is, the top right in the figure, the outside edge of the flat slopes upward. This is important, as it gives clearance to the metal behind the cutting edge of the drill. Having pointed the end like this, we get it red hot in the fire or gas flame and quickly plunge it into water.

 
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