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THREE:
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THREE:Milling relates to metal cutting with serrated rotary cutters, and differs in many respects from either planing or turning. The movement of the cutting edges can be more rapid than with tools which act continuously, because the edges are cooled during the intervals between each cut; that is, if a milling tool has twenty teeth, any single tooth or edge acts only from a fifteenth to a twentieth part of the time; and as the cutting distance or time of cutting is rarely long enough to generate much heat, the speed of such tools may be one-half greater than for turning, drilling, or planing tools. Another distinction between milling and other tools is the perfect and rigid manner in which the cutting edges are supported; they are short and blunt, besides being usually carried on short rigid mandrils. A result of this rigid support of the tools is seen in the length of the cutting edges that can be employed, which are sometimes four inches or more in length. It is true the amount of material cut away in milling is much less than the edge movement will indicate when compared with turning or planing; yet the displacing capacity of a milling machine exceeds that of either a lathe or a planing machine. Theoretically the cutting or displacing capacity of any metal or wood cutting machine, is as the length of the edges multiplied into the speed of their cutting movement; a rule which applies very uniformly in wood cutting, and also in metal cutting within certain limits; but the strains that arise in metal cutting are so great that they may exceed all means of resisting them either in the material acted upon, or in the means of supporting tools, so that the length of cutting edges is limited. In turning chilled rolls at Pittsburg, [141] tools to six inches wide are employed, and the effect produced is as the length of the edge; but the depth of the cut is slight, and the operation is only possible because of the extreme rigidity of the pieces turned, and the tools being supported without movable joints as in common lathes.
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THREE:In regard to shaded elevations, it may be said that photography has superseded them for the purpose of illustrating completed machines, and but few establishments care to incur the expense of ink-shaded elevations. Shaded elevations cannot be made with various degrees of care, and in a longer or shorter time; there is but one standard for them, and that is that such drawings should be made with great care and skill. Imperfect shaded elevations, although they may surprise and please the unskilled, are execrable in the eyes of a draughtsman or an engineer; and as the making of shaded elevations can be of but little assistance to an apprentice draughtsman, it is better to save the time that must be spent in order to make such drawings, and apply the same study and time to other matters of greater importance.An excellent plan to retain what is learned, is to make notes. There is nothing will assist the memory more in learning mechanics than to write down facts as they are learned, even if such memoranda are never referred to after they are made.
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THREE:Plato was born in the year 429, or according to some accounts 427, and died 347 B.C. Few incidents in his biography can be fixed with any certainty; but for our purpose the most general facts are also the most interesting, and about these we have tolerably trustworthy information. His family was one of the noblest in Athens, being connected on the father��s side with Codrus, and on the mother��s with Solon; while two of his kinsmen, Critias and Charmides, were among the chiefs of the oligarchic party. It is uncertain whether he inherited any considerable property, nor is the question one of much importance. It seems clear that he enjoyed the best education Athens could afford, and that through life he possessed a competence sufficient to relieve him from the cares of material existence. Possibly the preference which he expressed, when far advanced in life, for moderate health and190 wealth arose from having experienced those advantages himself. If the busts which bear his name are to be trusted, he was remarkably beautiful, and, like some other philosophers, very careful of his personal appearance. Perhaps some reminiscences of the admiration bestowed on himself may be mingled with those pictures of youthful loveliness and of its exciting effect on the imaginations of older men which give such grace and animation to his earliest dialogues. We know not whether as lover or beloved he passed unscathed through the storms of passion which he has so powerfully described, nor whether his apparently intimate acquaintance with them is due to divination or to regretful experience. We may pass by in silence whatever is related on this subject, with the certainty that, whether true or not, scandalous stories could not fail to be circulated about him.From Vis�� I went again across the Meuse to the road along the canal. Nearing Haccourt, I noticed that Fort Pontisse was actually silent, but Lierce still in full action. The Germans had mounted long-range guns on the hills between Lancey and Haccourt, whence they could place Fort Lierce under fire. A German officer, after some coaxing, allowed me to witness the operations for a short time. I found a place near some heavy guns, and sat down amid some underwood. The shooting from Lierce was very fierce, but only by the plumes of smoke could I tell whereabouts the fort might be. The shells came down near us, but during the half hour of my stop not one made a hit. They all fell short of us.

THREE:When we next hear of Aristotle he is at the Macedonian285 Court,174 acting as tutor to Alexander, the future conqueror of Asia, who remained under his charge between the ages of thirteen and sixteen years. The philosopher is more likely to have obtained this appointment by Court interest��his father was Court-physician to Alexander��s grandfather, Amyntas��than by his reputation, which could hardly have been made until several years afterwards. Much has been made of a connexion which, although it did not last very long, appeals strongly to the imagination, and opens a large field for surmise. The greatest speculative and the greatest practical genius of that age��some might say of all ages��could not, one would think, come into such close contact without leaving a deep impression on each other. Accordingly, the philosopher is supposed to have prepared the hero for his future destinies. Milton has told us how Aristotle ��bred great Alexander to subdue the world.�� Hegel tells us that this was done by giving him the consciousness of himself, the full assurance of his own powers; for which purpose, it seems, the infinite daring of thought was required; and he observes that the result is a refutation of the silly talk about the practical inutility of philosophy.175 It would be unfortunate if philosophy had no better testimonial to show for herself than the character of Alexander. It is not the least merit of Grote��s History to have brought out in full relief the savage traits by which his conduct was marked from first to last. Arrogant, drunken, cruel, vindictive, and grossly superstitious, he united the vices of a Highland chieftain to the frenzy of an Oriental despot. No man ever stood further from the gravity, the gentleness, the moderation��in a word, the S?phrosyn�� of a true Hellenic hero. The time came when Aristotle himself would have run the most imminent personal risk had he been within the tyrant��s immediate grasp. His286 nephew, Callisthenes, had incurred deep displeasure by protesting against the servile adulation, or rather idolatry, which Alexander exacted from his attendants. A charge of conspiracy was trumped up against him, and even the exculpatory evidence, taken under torture, of his alleged accomplices did not save him. ��I will punish the sophist,�� wrote Alexander, ��and those who sent him out.�� It was understood that his old tutor was included in the threat. Fortunately, as Grote observes, Aristotle was not at Ecbatana but at Athens; he therefore escaped the fate of Callisthenes, who suffered death in circumstances, according to some accounts, of great atrocity.Fourth.��Cores, where used, how vented, how supported in the mould, and I will add how made, because cores that are of an irregular form are often more expensive than external moulds, including the patterns. The expense of patterns is often greatly reduced, but is sometimes increased, by the use of cores, which may be employed to cheapen patterns, add to their durability, or to ensure sound castings.

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