ENGLISH 京香英文名字Cutting, as a process in converting material, includes the force to propel cutting edges, means to guide and control their action, and mechanism to sustain and adjust the material acted upon. In cutting with hand tools, the operator performs the two functions of propelling and guiding the tools with his hands; but in what  is called power operations, machines are made to perform these functions. In nearly all processes machines have supplanted hand labour, and it may be noticed in the history and development of machine tools that much has been lost in too closely imitating hand operations when machines were first applied. To be profitable, machines must either employ more force, guide tools with more accuracy, or move them at greater speed, than is attainable by hand. Increased speed may, although more seldom, be an object in the employment of machinery, as well as the guidance of implements or increased force in propelling them. The hands of workmen are not only limited as to the power that may be exerted, and unable to guide tools with accuracy, but are also limited to a slow rate of movement, so that machines can be employed with great advantage in many operations where neither the force nor guidance of tools are wanting.Suddenly several shots sounded in the neighbourhood. The three took their rifles and looked round, somewhat scared. They assured me that they would protect me. If there had been occasion for it, it would have been against their own comrades,117 for a troop of soldiers came sailing along, swinging about their rifles and shooting at the burning houses as they walked on, without rhyme or reason, anyhow and anywhere. These were drunk also. At last I was able to shake off my "friends," and got through another street into the market-place, at the town-hall and St. Peter's Church. The beautiful town-hall happily was not destroyed, as the first reports intimated, but St. Peter's had been damaged most cruelly. The spire had disappeared, the roof collapsed, windows broken, the altar burned, the pulpit badly damaged, and so forth. The two last-named parts were fine works of art.
My little protge was, however, soon very tired and complained that her feet ached. I had to carry her for nearly a mile and a half before we arrived at the Netherland Custom House, where I left her behind, as she was now safe. I went on to Maastricht alone, wired to my paper, and then saw the worried, but soon extremely happy parents of the little girl. They went at once to the Netherland frontier to take their child home.Modern engineers of the abler class are so thoroughly in accord in this matter of ornamentation, both in opinion and practice, that the subject hardly requires to be mentioned, and it will be no disadvantage for a learner to commence by cultivating a contempt for whatever has no useful purpose. Of existing practice it may be said, that in what may be called industrial machinery, the amount of ornamentation is inverse as the amount of engineering skill employed in preparing designs.As a means for transmitting power, shafts afford the very important advantage that power can be easily taken off at any point throughout their length, by means of pulleys or gearing, also in forming a positive connection between the motive-power and machines, or between the different parts of machines. The capacity of shafts in resisting torsional strain is as  the cube of their diameter, and the amount of torsional deflection in shafts is as their length. The torsional capacity being based upon the diameter, often leads to the construction of what may be termed diminishing shafts, lines in which the diameter of the several sections are diminished as the distance from the driving power increases, and as the duty to be performed becomes less. This plan of arranging line shafting has been and is yet quite common, but certainly was never arrived at by careful observation. Almost every plan of construction has both advantages and disadvantages, and the best means of determining the excess of either, in any case, is to first arrive at all the conditions as near as possible, then form a "trial balance," putting the advantages on one side and the disadvantages on the other, and footing up the sums for comparison. Dealing with this matter of shafts of uniform diameter and shafts of varying diameter in this way, there may be found in favour of the latter plan a little saving of material and a slight reduction of friction as advantages. The saving of material relates only to first cost, because the expense of fitting is greater in constructing shafts when the diameters of the different pieces vary; the friction, considering that the same velocity throughout must be assumed, is scarcely worth estimating.
Fourth. The arrangement of the parts of a combination machine have to be modified by the relations between them, instead of being adapted directly to the work to be performed.CHAPTER XXXIX. DESIGNING MACHINES.
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Gravity, or "overshot" wheels, as they are called, for some reasons will seem to be the most effective, and capable of utilising the whole effect due to the gravity of the water; but in practice this is not the case, and it is only under peculiar conditions that wheels of this class are preferable to turbine wheels, and in no case will they give out a greater per cent. of power than turbine wheels of the best class. The reasons for this will be apparent by examining the conditions of their operation."Not at all! If you step outside, you can see them standing, ten minutes from here. Near Lixhe they threw a bridge across the Meuse. It is the third already which they put down, for each time they are smashed from the fort. Oh, it is horrible; there must surely fall a number of dead, and here we have seen corpses in the Meuse already.... But I do not understand how you ventured to come here...."
Is it thinkable that persons in that frame of mind would take up arms and invite the enemy's revenge upon themselves and those near and dear to them, a revenge of which they were so mortally afraid?"The town-clerk, Eug. Marguery.
The shelling went on during the night, and all that time the inhabitants remained in their cellars."Tell me, father," he began, "did you allow this man by your side to stay the night at your house?"Good fitting is often not so much a question of skill as of the standard which a workman has fixed in his mind, and to which all that he does will more or less conform. If this standard is one of exactness and precision, all that is performed, whether it be filing, turning, planing, or drawing, will come to this standard. This faculty of mind can be defined no further than to say that it is an aversion to whatever is imperfect, and a love for what  is exact and precise. There is no faculty which has so much to do with success in mechanical pursuits, nor is there any trait more susceptible of cultivation. Methodical exactness, reasoning, and persistence are the powers which lead to proficiency in engineering pursuits.
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From this it may be seen that there must occur a great loss of power in operating on large pieces, for whatever force is absorbed by inertia has no effect on the underside. By watching a smith using a hand hammer it will be seen that whenever a piece operated upon is heavier than the hammer employed, but little if any effect is produced on the anvil or bottom surface, nor is this loss of effect the only one. The expense of heating, which generally exceeds that of shaping forgings, is directly as the amount of shaping that may be done at each heat; and consequently, if the two sides of a piece, instead of one, can be equally acted upon, one-half the heating will be saved.I then tried to find the nunnery of the S?urs de la Misricorde, where one of my cousins had taken the veil. At last, in the Rue des Clarisses I found the huge door of the monastery, and rang the bell. After a few moments a small trellised shutter in the stout door was opened ajar, and a tremulous voice asked in French what I wanted. I assumed that42 it was one of the nuns, but I could see nothing through that narrow jar.40
Having assumed a certain work to do, the cutting of tooth racks ? in. pitch, and 3 in. face, the first thing to be considered will be, is the machine to be a special one, or one of general adaptation? This question has to do, first, with the functions of the machine in the way of adapting it to the cutting of racks of various sizes, or to performing other kinds of work, and secondly, as to the completeness of the machine; for if it were to be a standard one, instead of being adapted only to a special purpose, there are many expensive additions to be supplied which can be omitted in a special machine. It will be assumed in the present case that a special machine is to be constructed for a particular duty only.With a thorough knowledge of practical machine operation, and an acquaintance with existing practice, an engineer proceeding upon such a plan, will, if he does not overlook some of the conditions, be able to generate designs which may remain without much modification or change, so long as the purpose to which the machinery is directed remains the same.
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