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    Software name: appdown
    Software type: Microsoft Framwork

    size: 86MB


    Software instructions

      The prevailing custom of casting machine frames in one piece, or in as few pieces as possible, leads to a great deal of bar-boring, most of which can be performed accurately enough by boring bars supported in and fed through bearings. By setting up temporary bearings to support boring-bars, and improvising means of driving and feeding, most of the boring on machine frames can be performed on floors or sole plates and independent of boring machines and lathes. There are but few cases in which the importance of studying the principles of tool action is more clearly demonstrated than in this matter of boring; even long practical experience seldom leads to a thorough understanding of the [139] various problems which it involves.Having thus far treated of such general principles and facts connected with practical mechanics as might properly precede, and be of use in, the study of actual manipulation in a workshop, we come next to casting, forging, and finishing, with other details that involve manual as well as mental skill, and to which the term "processes" will apply.

      Another peculiar feature in trip-hammers is the rapidity with which crystallisation takes place in the attachments for holding the die blocks to the helves, where no elastic medium can be interposed to break the concussion of the dies. Bolts to pass through the helve, although made from the most fibrous Swedish iron, will on some kinds of work not last for more than ten days' use, and often break in a single day. The safest mode of attaching die blocks, and the one most common, is to forge them solid, with an eye or a band to surround the end of the helve.

      I am not aware that the derivation of our standard measures has been, in an historical way, as the foregoing remarks will indicate, nor is it the purpose here to follow such history. A reader, whose attention is directed to the subject, will find no trouble in tracing the matter from other sources. The present object is to show what a wonderful series of connections can be traced from so simple a tool as a measuring gauge, and how abstruse, in fact, are many apparently simple things, often regarded as not worth a thought beyond their practical application.Already from a distance with much fuss they signalled to me to stop, and of course I obeyed at once. Two men dismounted, came to me in a perfect rage, and, without asking who I was or what I was doing, cut my tyres to pieces in several98 places; they abused me with wild gesticulations and threats, jumped on their horses, and rode off. I dragged my wretched vehicle with its stabbed tyres a little distance, but then met a second patrol, who showed still greater indignation, and destroyed it altogether.

      Shaping machines are generally provided with adjustable vices, devices for planing circular forms, and other details which cannot be so conveniently employed with planing machines. Another feature of shaping machines is a positive range of the cutting stroke produced by crank motion, which permits tools to be stopped with precision at any point; this admits of planing [136] slots, keyways, and such work as cannot well be performed upon common planing machines.In constructing patterns where it is optional whether to employ cores or not, and in preparing drawings for castings which may have either a ribbed or a cored section, it is nearly always best to employ cores. The usual estimate of the difference between the cost of moulding rib and cored sections, as well as of skeleton and cored patterns, is wrong. The expense of cores is often balanced by the advantage of having an 'open mould,' that is accessible for repairs or facing, and by the greater durability and convenience of the solid patterns. Taking, for example, a column, or box frame for machinery, that might be made either with a rib or a cored section, it would at first thought seem that patterns for a cored casting would cost much more by reason of the core-boxes; but it must be remembered that in most patterns labour is the principal expense, and what is lost in the extra lumber required for a core-box or in making a solid pattern is in many cases more than represented in the greater amount of labour required to construct a rib pattern.

      Thumb-tacks are of but little use in mechanical drawing except for the most temporary purposes, and may very well be dispensed with altogether; they injure the draughting-boards, obstruct the squares, and disfigure the sheets.

      At seven o'clock in the evening I entered Lige; and so far I had achieved my end.Second.The steam establishes the greatest possible elasticity in the connection between a hammer and the driving power, and at the same time serves to cushion the blows at both the top and bottom of the stroke, or on the top only, as occasion may require.


      CHAPTER XXXII. SLOTTING MACHINES.Another difference between solid and expanding dies, which may be pointed out, is in the firmness with which the cutting edges are held. With a solid die, the edges or teeth being all combined in one solid piece, are firmly held in a fixed position; while with expanding dies their position has to be maintained by mechanical devices which are liable to yield under the pressure which arises in cutting. The result is, that the precision with which a screwing machine with movable dies will act, is dependent upon the strength of the 'abutment' behind the dies, which should be a hard unyielding surface with as much area as possible.


      "And what do you want to write about?"Milling tools are employed at Crewe for roughing out the slots in locomotive crank axles. A number of detachable tools are mounted on a strong disc, so that four to six will act at one time; in this way the displacement exceeds what a lathe can perform when acting continuously with two tools. Rotary planing machines constructed on the milling principle, have been tried for plane surfaces, but with indifferent success, except for rough work.


      (1.) Under what conditions is hydraulic apparatus a suitable means for transmitting power?(2.) To what class of operations is hydraulic apparatus mostly applied?(3.) Why is not water as suitable a medium as air or steam in transmitting power for general purposes?CHAPTER IX. WIND-POWER.