ONE:The similarity of the operations carried on in all works directed to the manufacture of machinery, and the kind of knowledge that is required in planning and conducting such works, would lead us to suppose that at least as much system would exist in machine shops as in other manufacturing establishments, which is certainly not the case. There is, however, this difference to be considered: that whereas many kinds of establishments can be arranged at the beginning for a specific amount of business, machine shops generally grow up around a nucleus, and are gradually extended as their reputation and the demands for their productions increase; besides, the variety of operations required in an engineering establishment, and change from one class of work to another, are apt to lead to a confusion in arrangement, which is too often promoted, or at least not prevented, by insufficient estimates of the cost of handling and moving material.Machines and tools operating by percussive action, although they comprise a numerous class, and are applied in nearly all mechanical operations, have never received that amount of attention in text-books which the importance of the machines and their extensive use calls for. Such machines have not even been set off as a class and treated of separately, although the distinction is quite clear between machines with percussive action, and those with what may be termed direct action, both in the manner of operating and in the general plans of construction. There is, of course, no lack of formul? for determining the measure of force, and computing the dynamic effect of percussive machines acting against a measured or assumed resistance, and so on; but this is not what is meant. There are certain conditions in the operation of machines, such as the strains which fall upon supporting frames, the effect produced upon malleable material when struck or pressed, and more especially of conditions which may render percussive or positive acting machines applicable to certain purposes; but little explanation has been given which is of value to practical men.
ONE:The trembling fit passed away, the woman was herself again. All the same, Balmayne was not without misgiving as he put his foot in the loop. But the crank of the windlass turned steadily and smoothly, the stone walls slid by, and presently the adventurer stood at the bottom of the well. There was no water, nothing but a slight dampness underfoot.
ONE:The traction of belts upon pulleys, like that of locomotive wheels upon railways, being incapable of demonstration except by actual experience, for a long time hindered the introduction of belts as a means of transmitting motion and power except in cases when gearing or shafts could not be employed. Motion is named separately, because with many kinds of machinery that are driven at high speedsuch as wood machinesthe transmission of rapid movement must be considered as well as power, and in ordinary practice it is only by means of belts that such high speeds may be communicated from one shaft to another.Jeff called and signaled that all was ready. Larry summoned Sandy but the latter lingered, while Dick, a little sorry he had taunted so much, followed Larry toward the waiting airplane. But Sandy, scowling, hesitated whether he would go or be angry and refuse to join the Sky Patrol. Then, as he clambered onto the forward bracing of the under wing and leaned on the cockpit cowling, his face assumed a startled, intent expression.
