Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 113

THE most important tool among those implied by the chapter heading is the hand hammer, and at the same time it is the most simple. The hammer may be regarded as a weight at one end of a rod. Speaking generally, the effect is produced by allowing the weight head to fall through a space, and then come in contact with the material to be influenced by the blow. Perhaps the objects to be accomplished by the blows of hammers are more varied than those to be effected by any other single tool. It is doubtful whether any handicraftsman carries through any branch of his trade without using some kind of hammer. This may be anything, from the heavy two-handed maul to the smallest tapping hammers of the jeweller and watch-maker, file-maker, and diamond-splitter. It may be well to discuss the manner in which the power of a hammer actually is developed. The development of power, according to Rigg’s Cantor Lectures, takes place at the instant of contact of the moving hammer with the struck body. Such contacts as those of hammers belong to the department of mechanical philosophy called “impact.” Impact is pressure of short duration—so short that, compared with the time in which the velocity on the impinging body is being acquired, it is inappreciable; similarly the space passed through by the hammer-head after impact is almost inappreciable when compared with the space passed through before impact. It may assist the worker to realise the source as well as the magnitude of the power of a hammer, if the following simple experiment be tried. Attempt to drive a nail vertically into a horizontal piece of timber by the statical effect of the simple pressure of a load on the head of the nail, the load being placed on the head gently, and measure the depth to which the nail is thus moved. Again, let the same nail, under the same circumstances, be driven to the same depth by the impact of the hammer-head, then it may for the present purpose be said that the load placed on the nail is a representative statical measure of the impact of the hammer. This is a representative and an approximately accurate method for comparing the effects of hammers under all ordinary circumstances, though the method is not faultless.