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    Software name: appdown
    Software type: Microsoft Framwork

    size: 525MB


    Software instructions

      To follow out the application of power to the propulsion of vessels and trains, with the many abstruse problems that would of necessity be involved, would be to carry this work far beyond the limits within which it is most likely to be useful to the apprentice engineer; besides, it would be going beyond what can properly be termed manipulation.

      Leaving out the matter of a positive relative movement between shafts, which belts as a means of transmitting power cannot insure, there are the following conditions that must be considered in determining whether belts or other means should be employed in transmitting power from one machine to another or between the parts of machines.

      The eye fails to detect variations in size, even by comparison, long before we reach the necessary precision in common fitting. Even by comparison with figured scales or measuring with rules, the difference between a proper and a spoiled fit is not discernible by sight.

      A milling tool with twenty edges should represent as much wearing capacity as a like number of separate tools, and may be said to equal twenty duplicate tools; hence, in cutting grooves, notches, or similar work, a milling tool is equivalent to a large number of duplicate single tools, which cannot be made or set with the same truth; so that milling secures accuracy and duplication, objects which are in many cases more important than speed.The latter seems a plausible theory, and perhaps a correct one; but there are two facts in connection with the operation of reaction water-wheels which seem to controvert the latter and favour the first theory, namely, that reaction wheels in actual practice seldom utilise more than forty per cent. of useful effect from the water, and that their speed may exceed the initial velocity of the water. With this the subject is left as one for argument or investigation on the part of the reader.

      Machine motion is mainly rotary; and as rotary motion is accomplished by cylindrical parts such as shafts, bearings, pulleys and wheels, we find that the greater share of machine tools are directed to preparing cylindrical forms. If we note the area of the turned, bored and drilled surface in ordinary machinery, and compare with the amount of planed surface, we will find the former not less than as two to one in the finer class of machinery, and as three to one in the coarser class; from this may be estimated approximately the proportion of tools required for operating on cylindrical surfaces and plane surfaces; assuming the cutting tools to have the same capacity in the two cases, the proportion will be as three to one. This difference between the number of machines required for cylindrical and plane surfaces is farther increased, when we consider that tools act continually on cylindrical surfaces and intermittently on plane surfaces.

      Aside from the cost or difficulty of obtaining ground sufficient to carry out plans for engineering establishments, the diversity of their arrangement met with, even in those of modern construction, is no doubt owing to a want of reasoning from general premises. There is always a strong tendency to accommodate local conditions, and not unfrequently the details of shop manipulation are quite overlooked, or are not understood by those who arrange buildings.

      "No, I've none to sell."Chasing operations being lathe work, and involving no principles not already noticed, what is said further will be in reference to die-cutting or bolt-threading machines, which, simple as they may appear to the unskilled, involve, nevertheless [144] many intricacies which will not appear upon superficial examination.


      This assumed, the scheme is complete, so far as the relative movement of the hammer-drop and the valve, but there must be some plan of giving motion to this added mechanism. In many examples there may be seen parts of machinery which continue in motion after the force which propels them has ceased to act; cannon balls are thrown for miles, the impelling force acting for a few feet only; a weaver's shuttle performs nearly its whole flight after the driver has stopped. In the present case, it is therefore evident that an independent or subsequent movement of the valves may be obtained by the momentum of some part set in motion during the descent of the hammer-head."Sister," I said, "I am a cousin of S?ur Eulalie, and should like to see her, to know how she is and take her greetings to her family in The Netherlands."


      Most of the difficulties which formerly pertained to drilling are now removed by machine-made drills which are manufactured and sold as an article of trade. Such drills do not require dressing and tempering or fitting to size after they are in use, make true holes, are more rigid than common solid shank drills, and will drill to a considerable depth without clogging.


      I was scarcely outside the townlet when I met another little group of refugees, probably all members of one family. The mother was being supported by her daughters, all wept, and nervous exhaustion made them totter as they walked. Every moment the mother looked back pitifully at the conflagration which devoured all around, including her slender property, for which she had worked so many years.Dimension lines should be in blue, but may be in red. Where to put them is a great point in draughting. To know where dimensions are required involves a knowledge of fitting and pattern-making, and cannot well be explained; it must be learned in practice. The lines should be fine and clear, leaving a space in their centre for figures when there is room. The distribution of centre lines and dimensions over a drawing must be carefully studied, for the double purpose of giving it a good appearance and to avoid confusion. Figures should be made like printed numerals; they are much better understood by the workman, look more artistic, and when once learned require but little if any more time than written figures. If the scale employed is feet and inches, dimensions to three feet should be in inches, and above this in feet and inches; this corresponds to shop custom, and is more comprehensive to the workman, however wrong it may be according to other standards.