时间:2021-01-21 09:41:08



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          On the first houses of the town large bills had been stuck, intimating that they were a Netherlander's property, but obviously that had not impressed the tipsy soldiers to any extent, for they had been wrecked all the same for the greater part.ぅイい



          The sudden and varied resistance to line shafts tends to loosen couplings, destroy gearing, and produce sudden strains that are unknown in other cases; and shafting arranged with the usual proportions for transmitting power will soon fail if applied to driving trip-hammers. Rigid connections or metal attachments ace impracticable, and a slipping belt arranged so as to have the tension varied at will is the usual and almost the only successful means of transmitting power to hammers. The motion of trip-hammers is a curious problem; a head and die weighing, together with the irons for attaching them, one hundred pounds, will, with a helve eight feet long, strike from two to three hundred blows a minute. This speed exceeds anything that could be attained by a direct reciprocal motion given to the hammer-head by a crank, and far exceeds any rate of speed that would be assumed from theoretical inference. The hammer-helve being of wood, is elastic, and acts like a vibrating spring, its vibrations keeping in unison with the speed of the tripping points. The whole machine, in fact, must be constructed upon a principle of elasticity throughout, and in this regard stands as an exception to almost every other known machine. The framing for supporting the trunnions, which one without experience would suppose should be very rigid and solid, is found to answer best when composed of timber, and still better when this timber is laid up in a manner that allows the structure to spring and [107] yield. Starting at the dies, and following back through the details of a trip-hammer to the driving power, the apprentice may note how many parts contribute to this principle of elasticity: First—the wooden helve, both in front of and behind the trunnion; next—the trunnion bar, which is usually a flat section mounted on pivot points; third—the elasticity of the framing called the 'husk,' and finally the frictional belt. This will convey an idea of the elasticity required in connecting the hammer-head with the driving power, a matter to be borne in mind, as it will be again referred to.沥à伽カぅ




          The title of a drawing is a feature that has much to do with its appearance, and the impression conveyed to the mind of an observer. While it can add nothing to the real value of a drawing, it is so easy to make plain letters, that the apprentice is urged to learn this as soon as he begins to draw; not to make fancy letters, nor indeed any kind except plain block letters, which can be rapidly laid out and finished, and consequently employed to a greater extent. By drawing six parallel lines, making five spaces, and then crossing them with equidistant lines, the points and angles in block letters are determined; after a little practice, it becomes the work of but a few minutes to put down a title or other matter on a drawing so that it can be seen and read at a glance in searching for sheets or details.烘搀ゥ


          The advantages gained by milling, as stated, are speed, duplication, and accuracy; the disadvantages are the expense of preparing tools and their perishability.けォ赔窑


          Her reserve told me that I would not get much information here, and, finishing my beer, I asked:痄绀イぴ




          To this proposition another may be added, that shop processes may be systematised or not, as they consist in duplication, or the performance of certain operations repeatedly in the same manner. [101] It has been shown in the case of patterns that there could be no fixed rules as to their quality or the mode of constructing them, and that how to construct patterns is a matter of special knowledge and skill.扶螗

          Shaping machines are divided into two classes, one modification with a lateral feed of the tools and cutter bar, technically called "travelling head machines," the other class with a feed motion of the table which supports the work, called table-feeding machines. The first modification is adapted for long pieces to be planed transversely, such as toothed racks, connecting rods, and similar work; the second class to shorter pieces where much hand adjustment is required.ぅ≥衰いぬ

            2021-01-21 09:41:08