THE carpenter has a large range of nails of all shapes and sizes at his disposal for use on the roughest structural work or the most delicate jointing of fragile woodwork. Excluding the use of nails for delicate jointing, where screws cannot be utilized, nails are generally employed only in rough joinery, but no hard and fast rule can be applied to their incidental use for special work. Screws are, for instance, more or less essential for parts that may have to be dismantled without damage at a later date, but their use is not confined to this function only. In fixing parts by nailing, a good deal of force has to be applied by hammer blows; not all jobs will stand this. Another rough division may be made; nails are suitable for fixing one member to another at right angles, where the nail has to go into end grain. There is plenty of depth to allow a sufficiently long nail to be driven in, whereas a screw might not grip at all. If we wish to fix two fairly thin members together flat face to flat face, the only feasible way of doing this with nails is to drive right through both members, letting the nail be long enough to protrude on the under side, and then to clench the nail with a hammer blow. This is a very rough method, but is much used for certain work, for example, in nailing the boards of a ledged door to the ledges or cross members. For good class work screws are usually employed, provided the thickness of the ledge is sufficient to give adequate depth for the screws.
Screws are used extensively for attaching locks, latches, bolts and all sorts of fittings and apparatus to woodwork. If the fitting has a countersunk hole for the screws, then the screws with countersunk heads, should be used. These are designed to be screwed in flush with the surface. Cuts and scratches may be sustained when using a latch or handle from which the heads of screws protrude, either as a result of careless fixing, or the use of a countersunk head when the plate of the fitting is not intended to take this type of head. When the plate has merely a plain hole, use the screws with a round head. On good class brasswork provided with countersunk holes there is an alternative to the simple countersunk head: this is a countersunk screw with a raised head. A neat and pleasing finish may be obtained by the use of this type of screw.
Screws for Heavy Work
Typical examples of fairly heavy screws are the countersunk and round head screws which are Gauge 20. They are made in lengths of 1 in. to 7in., though the lengths above 3 in. would have to be ordered, and would seldom be called for. Coach screws, used for heavy work, have a variety of uses; a typical one is, this being 2 in. long, by -j-in. Diameter at the shank. The head is square, to take a spanner; hexagonal headed screws are made, and are easier to turn in cramped quarters, since the spanner can be applied at six positions instead of four. The full range of diameters is from -¾ in. to 1 in.; lengths range from ½ in. to 8in., though only the stouter ones are obtainable in the longer lengths. The½ in., ¾ in., and½ in. thicknesses are those most likely to be needed, up to about 4in. Long. Stout gauge screws of ordinary pattern are difficult to drive, so that coach screws are better wherever they can conveniently be employed.
Choice of Screws
The type of metal used in the manufacture of screws influences their use. Brass screws are much less strong than steel screws. When turning a brass screw into oak it is quite easy to break the screw, or to break off one side of its head, unless the hole has been bored carefully to give an easy clearance to the shank, and also to leave enough material for the worm to bite into without making the hole too small. In driving a screw we are, in effect, driving in a long, tapering wedge. The spiral arrangement of the worm enables the force to be applied very gradually. If a suitable hole is made for the worm, this hole, of course, being smaller in diameter than the top part, bored to clear the shank, the screw cuts a counter- part thread in the wood. Only £ combined twisting and pulling motion will pull out the screw, unless very great force is used in proportion to the size of the parts and the natLire of the timber.
Early wood screws lacked the gimlet point, and had to be forced into the timber with subsequent danger of splitting the surrounding wood. The gimlet point, however, assists the entry of the screw intc the wood, by providing a lead for the worm thread, once it is given a good start. Where brass screws would naturally be preferred on account of appearance, and there is a doubt of their being strong enough, we can use brass plated mild steel screws. These will rust, of course, if used for exposed work or in places where conditions are conducive to dampness, but for all ordinary purposes they are satisfactory.
Always use steel screws where a strong job is desired. For outdoor work, galvanized screws should be used. Brass screws would naturally be used for indoor work where brass fittings are to be used; also for all sorts of small fancy articles and for furniture. Nickelled, chromed and coppered finishes are available for many sorts and sizes; aluminium screws should be used for aluminium fittings.
It is common knowledge that most screws have a plain shank between the head and top end of the worm thread, that is, the worm does not start until some little distance down from the head. This is satisfactory for fastening wood to wood, or for attaching fairly thick plates or fittings, but where thin fittings, or mirror plates are concerned, we need screws which are wormed right up to the head, or nearly so. Such screws can be obtained from most ironmongers, in lengths and gauges suitable for the purpose mentioned. This is an important point to observe when using wall plugs: the shank of the screw should not enter the plug, or it may cause the latter to twist round and become loose. When screws of the proper type are not available, cut the plug a little short, and push it in so that room is left for the shank before reaching the plug.
For most household purposes, screws in Gauges 6 and 8 are suitable. Gauge 12 is the one for workshop jobs such as making up a bench or a sawing horse. It is seldom that anything stouter will be needed. For the innumerable small or delicate jobs it is possible to get the inexpensive small screws in Gauges 00, o, 1, 2 and 3, both round head and countersunk. Purchase them in the original box or carton, and they are less likely to be mislaid. Larger screws can be purchased two or three dozen at a time, and should be kept in small boxes or tins. If they have to be mixed, put a long size and a short in the same container; they will be easier to pick out than if several very near sizes are stocked together.
Nails for Household Jobs
The wire nails will meet all general needs. Round nails, in lengths of 1 in. to 3in., can be bought in half-pound lota and put into some simple box or tray ready for use. Oval nails are better for some purposes, but the head has less holding power than the bigger round head of the ordinary wire nail. Where a very incon- spicuous nail is desired, use the lost head type; this has a round shank and a small head, like that of the panel pin. Panel pins, nominally intended for securing panels in joinery work, are useful for a variety of home jobs. Amateurs often confuse them with veneer pins, which are much finer and, if anything, more useful. When fine pins or nails are required, ask the ironmonger to display the various types.
Clout nails have large round heads and are short in the shank; they are used for fixing felt to wood, and similar jobs. There are special nails (galvanized) for fixing corrugated iron to woodwork, and curved washers are sold for use with them. Galvanized screws can be used as an alternative for corrugated sheeting; and there is also a drive-screw, or screw-nail which is driven in like a nail and twists during this operation.
Gimp pins are made in various short lengths; besides the nominal use for tacking gimp edging over upholstery, they are handy for many household purposes. Cut tacks are usually of poor quality and vary much in shape and finish; a better quality is made and should be used for preference. For fastening down carpets and other floor coverings use carpet nails with large heads. When nails with small heads are used the carpet is likely to be torn in the process of lifting for spring cleaning.
Always bore starting holes on woodwork of importance. If nails are used to attach one part to another, a clearing hole is needed in the top member, and should continue a little way into the underneath part to give guidance.