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    Software name: appdown
    Software type: Microsoft Framwork

    size: 426MB

    Lanuage:Englist

    Software instructions


      Machines with direct action, such as punches, shears, or rolls, require first a train of mechanism of some kind to reduce the motion from the driving power so as to attain force; and secondly, [105] this force must be balanced or resisted by strong framing, shafts, and bearings. A punching-machine, for example, must have framing strong enough to resist a thrust equal to the force applied to the work; hence the frames of such machines are always a huge mass, disposed in the most advantageous way to meet and resist this reactive force, while the main details of a drop-machine capable of exerting an equal force consist only of a block and a pair of guides to direct its course.


      I showed them the way to Eysden, and they had80 scarcely started when a cavalry patrol came racing on, the men tipsy and their seat rather unstable. Seeing the refugees, they aimed their rifles at them and roared "Hands up!" The poor creatures not only put up their hands, but fell on their knees, and muttered incoherent words. The women folded their hands, and stretched them out to the cavalry, as if praying for mercy. The soldiers looked at the scene for a moment, burst out in a harsh laughter, spurred on their horses, and raced on without a word. Two of them stopped near me. I gave them, however, no time for threats, but quickly showed them the old pass to Vis. As soon as they saw the German writing they said: "All right!" and went off.CHAPTER VI

      [39]The officer went on shaking his head at my answers, and I felt as if this might be the end of my fine little adventure. But I could not tell him that I had gone to Lige with that permit for Vis!


      To conclude. The reader will understand that the difficulties and diversity of practice, in any branch of engineering, create similar or equal difficulties in explaining or reasoning about the operations; and the most that can be done in the limited space allotted here to the subject of moving material, is to point out some of the principles that should govern the construction and adaptation of handling machinery, from which the reader can take up the subject upon his own account, and follow it through the various examples that may come under notice.

      The inhabitants looked upon the church as a special sanctuary, as the bones of St. Hadelin were kept there. Before the fire these relics had been removed to the vicarage secretly, and then to St. Hadelin College, the only large building that escaped the general destruction next day.

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      In those first days many civilians were killed, and not only in Vis, but still more in the surrounding villages, Mouland and Berneaux, which were soon burnt down and where many a good man was brought low by the murderous bullets. The savage soldiers killed the cattle also, and a large number of carcases had been lying about for days.

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      Attention has been called to this case as one wherein the conditions of operation obviously furnish true data to govern the arrangement of machinery, instead of the determinable strains to which the parts are subjected, and as a good example of the importance of studying mechanical conditions from a practical and experimental point of view. If the general diameter of a shaft is based upon the exact amount of power to be transmitted, or if the diameter of a shaft at various parts is based upon the torsional stress that would be sustained at these points, such a shaft would not only fail to meet the conditions of practical use, but would cost more by attempting such an adaptation. The regular working strain to which shafts are subjected is inversely as the speed at which they run. This becomes a strong reason in favour of arranging shafts to run at a maximum speed, provided there was nothing more than first cost to consider; but there are other and more important conditions to be taken into account, principal among which are the required rate of movement where power is taken off to machines, and the endurance of bearings.It may also be mentioned that lathes constructed with angular guides, have usually such ways for the moving heads as well as for the carriages; this gives the advantage of firmly binding the [125] two sides of the frame together in fastening the moving head, which in effect becomes a strong girt across the frame; the carriages also have an equal and independent hold on both sides of a shear. In following this matter thus far, it may be seen how many conditions may have to be considered in reasoning about so apparently simple a matter as the form of ways for lathe carriages; we might even go on to many more points that have not been mentioned; but what has been explained will serve to show that the matter is not one of opinion alone, and that without practical advantages, machine tool-makers will not follow the most expensive of these two modes of mounting lathe carriages.

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      A drilling machine, adapted to the usual requirements of a machine fitting establishment, consists essentially of a spindle arranged to be driven at various speeds, with a movement for feeding the drills; a firm table set at right angles to the spindle, and arranged with a vertical adjustment to or from the spindle, and a compound adjustment in a horizontal plane. The simplicity of the mechanism required to operate drilling tools is such that it has permitted various modifications, such as column drills, radial drills, suspended drills, horizontal drills, bracket drills, multiple drills, and others.


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