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    Software name: appdown
    Software type: Microsoft Framwork

    size: 970MB

    Lanuage:Englist

    Software instructions

      CHAPTER XXXIII. SHAPING MACHINES.The fitting or finishing department of engineering establishments is generally regarded as the main one.


      Machine-drawing may in some respects be said to bear the same relation to mechanics that writing does to literature; persons may copy manuscript, or write from dictation, of what they do not understand; or a mechanical draughtsman may make drawings of a machine he does not understand; but neither such writing or drawing can have any value beyond that of ordinary labour. It is both necessary and expected that a draughtsman shall understand all the various processes of machine construction, and be familiar with the best examples that are furnished by modern practice.First.Durability, plans of construction and cost, which all amount to the same thing. To determine this point, there is to be considered the amount of use that the patterns are likely to serve, whether they are for standard or special machines, and the quality of the castings so far as affected by the patterns. A first-class pattern, framed to withstand moisture and rapping, may cost twice as much as another that has the same outline, yet the cheaper pattern may answer almost as well to form a few moulds as an expensive one.


      Netherland soldiers and inhabitants of the village bustled about along the opposite river-bank. I shouted as loudly as possible; and when at last I succeeded in drawing their attention, I made them understand that I wanted to be pulled across in the little boat, which in ordinary times served as a ferry. A short consultation took place now on the opposite side, after which a soldier, who clearly possessed a strong voice, came as near as possible to the waterside and, making a trumpet of his two hands, roared:

      These remarks upon hammers are not introduced here as a matter of curiosity, nor with any intention of following mechanical principles beyond where they will explain actual manipulation, but as a means of directing attention to percussive acting machines generally, with which forging processes, as before explained, have an intimate connection.Every one who uses tools should understand how to temper them, whether they be for iron or wood. Experiments with tempered tools is the only means of determining the proper degree of hardness, and as smiths, except with their own tools, have to rely upon the explanations of others as to proper hardening, it follows that tempering is generally a source of complaint.

      "General Leman, Commander Naessens, and all the officers were splendid in their imperturbable courage. They found the words that went straight to the hearts of their men. These fellows looked more like bronze statues than human beings. The projectiles hammered at the walls and smashed huge pieces, penetrating into the parts near the entrance. The rest of the fort withstood splendidly the hurricane of hostile steel and fire. During the night the bombardment stopped, and then the commanding officer went to inspect the cupolas.


      A planing machine invented by Mr Bodmer in 1841, and since improved by Mr William Sellers of Philadelphia, is free from this elastic action of the platen, which is moved by a tangent wheel or screw pinion. In Bodmer's machine the shaft carrying the pinion was parallel to the platen, but in Sellers' machine is set on a shaft with its axis diagonal to the line of the platen movement, so that the teeth or threads of the pinion act partly by a screw motion, and partly by a progressive forward movement like the teeth of wheels. The rack on the platen of Mr Sellers' [134] machine is arranged with its teeth at a proper angle to balance the friction arising from the rubbing action of the pinion, which angle has been demonstrated as correct at 5°, the ordinary coefficient of friction; as the pinion-shaft is strongly supported at each side of the pinion, and the thrust of the cutting force falls mainly in the line of the pinion shaft, there is but little if any elasticity, so that the motion is positive and smooth.To avoid imperfection in the running spindles of lathes, or any lateral movement which might exist in the running bearings, there have been many attempts to construct lathes with still centres at both ends for the more accurate kinds of work. Such an arrangement would produce a true cylindrical rotation, but must at the same time involve mechanical complication to outweigh the object gained. It has besides been proved by practice that good fitting and good material for the bearings and spindles of lathes will insure all the accuracy which ordinary work demands.

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      4. The speed at which shafts should run is governed by their size, the nature of the machinery to be driven, and the kind of bearings in which they are supported.

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      CHAPTER XXXV. MILLING.

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