The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking. Paul N. Hasluck
oil, and rub the tool on it as usual. Fig. 450 shows a cheap and efficient form of carpenter’s hone, which is an excellent substitute for the oilstone. It consists of a strip of sheet zinc A, stretched over the wooden mount B, and screwed down at each end lengthways of the grain. To use the sharpener thus made it is necessary to sprinkle a little flour emery on the zinc, and moisten in the usual way with oil. For general purposes it will be found very handy, and will do the same work as the oilstone does in less time, but it will not leave the edge in quite such a finished condition as does a good oilstone. C, Fig. 450, shows a cover for the stone.
Fig. 450.—Oilstone Substitute.
NAILS, SCREWS, AND GLUE.
NAILS.
A NAIL is a pin or slender piece of metal used for driving through or into wood or other material to hold separate pieces together; or part of the nail is left projecting so that things may be hung on it. It may be of iron, steel, etc., and may be wrought, cast, or cut; or it may be of wire. In former practice, nails were said to be 6-lb., 8-lb., etc., according as 1,000 of the variety weighed 6 lb., 8 lb., etc.; hence such now meaningless terms as sixpenny, eightpenny, and tenpenny nails, in which “penny” is a corruption of “pound.” Nails consist of two parts, the head and the shank; and although they are mostly made of iron and steel, large numbers are also made of copper, zinc, etc. The varieties of nails number about 300, but the carpenter and joiner does not use many of these. Briefly the action of a nail is as follows. It is wedge-shaped so as to break through the fibres of the wood, and there it is held tightly by the elastic fibres, which endeavour to regain their original position, and so press tightly on the nail. The flattened out tops of nails known as the heads assist greatly in holding the nails in position, especially if there is any pulling strain at the opposite ends.
WHY A NAIL HOLDS.
A very simple experiment, to be made by anyone with a hammer and a few nails, will throw much light on the reason why a nail holds woodwork together. Take a piece of straight-grained deal, about 2 in. wide and 1 in. thick, and mark a line along the centre of one of the narrow sides; drive in various nails in a row, about 1 in. apart, and then split the piece down the middle line so as to expose the nails throughout their length. The smooth wire nails called French nails will be found to have penetrated the wood with very little disturbance of the surrounding fibres, and, as a consequence, they go in easily, and will draw out again with great facility. What hold they have is chiefly by friction from the compressed fibres reacting against the sides of the nails. On the other hand, a 3-in. floor brad, which has a flat square point, produces great disturbance in the fibres. Immediately under the point the fibres are crushed and pushed downwards, carrying others partly down with them so that they press against the sides, and at the same time point downwards. It will be observed that every little group of fibres is like a strut pushing against the nail, and preventing its withdrawal. This experiment may be varied indefinitely; and the effect of boring holes before driving the nails can be studied. The difference also between the holes produced by a gimlet, a sharp bradawl, and a blunt bradawl will be instructive.
HOLDING POWEES OF NAILS.
The holding powers of nails, of course, vary with the shape of the nails and the kind of wood into which they are driven. The following statements have been made as the result of tests carried out at Sibley College, Cornell University:—Cut nails are superior to wire nails in all positions, and if pointed they would be 30 per cent. more efficient in direct tension. The advantage of a wire nail is the sharp point; without a point it would have but one-half its ordinary holding power. The surface of the nail should be slightly rough, but not barbed; barbing decreases the efficiency of cut nails by about 32 per cent. Nails should be wedge-shaped in both directions when there are no special dangers of splitting. The length of nails to be used in tension should be about three times the thickness of the thinnest piece nailed. Nails usually hold about 50 per cent. more when driven perpendicularly to the grain than when parallel to it. When subjected to shock, nails have been found to hold less than one-twelfth the dead load they will stand when weight is applied gradually. Professor Soule has proved that, under all ordinary conditions, cut nails hold better than wire nails. Holding effect increases with the length of a nail, but not in proportions expressible by any simple formula. When a cut nail is properly pointed, its hold is increased by 33 per cent. Nails driven into certain woods, Californian redwood for example, will take a better hold the longer they are left in; the reverse happens with other woods, Douglas pine for instance. Deals, when nailed to a block, show about equal holding powers for equal areas of nail, whether a few thick nails or a greater number of thin nails are employed; the advantage is slightly in favour of the thick nails. Haupt, in his “Military Bridges,” gives a table showing the holding power of wrought iron nails weighing 77 to the lb., and having a length of about 3 in. The nails were driven through a 1-in. board into a block from which it was dragged in a direction perpendicular to length of nails. Taking a pine plank nailed to a pine block, with eight nails to the square foot, the average breaking weight per nail was found to be 380 lb.; in oak the power was 415 lb.; with twelve nails per square foot the holding power was 542·5 lb.; and with six nails in pine 463·5 lb. The highest result was obtained for twelve nails per square foot in pine, the breaking weight being 612 lb. per nail. The average strength decreased with the increase of surface. In Bevan’s experiments the force in pounds required to extract “threepenny” brads from dry Christiania deal, at right angles to grain of wood, was found to be 58 lb.; the force required to draw a wrought-iron “sixpenny” nail was 187 lb., the length forced into the wood being 1 in. The relative adhesion, when the nail is driven transversely and longitudinally, is in deal about 2 to 1. To extract a common “sixpenny” nail from a depth of 1 in., in dry beech, across grain, required 167 lb.; in dry Christiania deal, across grain, 187 lb., and with grain 87 lb.; in elm the required force was 327 lb. across grain, and 257 lb. with grain; and in oak 507 lb. across grain. From Lieutenant Fraser’s experiments, it would appear that the holding power of spike nails in fir is 460 lb. to 730 lb. per inch in length; while the adhesive power of “wood screws” 2 in. long and 22·1 diameter, at exterior of threads, 12 to the inch, driven into 1/2-in. board, was 790 lb. in hard wood, and about half that amount in soft wood.
CUT CLASP NAILS.
Of the various kinds of nails commonly used in wood-working, the cut clasp (Fig. 451), machine-made from a sheet of iron, must rank first. These nails, if of a good brand, may be used for almost any purpose; being cut clean by the machine, they are not liable to split the work. The head is not very large, and when the nail has been inserted, should be punched just below the surface of the wood. Cut clasp nails are typical of many old-fashioned nails, which are, however, gradually being displaced by the newer serrated steel brads. A good nail of the same class is made from steel, very tough, and therefore useful for many purposes, the increase in cost being very small. Cut clasp nails may be had of almost any size, from 3/4 in. to 6 in. in length.
Fig. 451. Cut Clasp Nail.
Fig. 452. Rose-head Nail.
Fig. 453. Wrought Clasp Nail.
Fig. 454. Wrought Clasp Nail.