Draughting, or drawing, as it is more commonly called, is a means by which mental conceptions are conveyed from one person to another; it is the language of mechanics, and takes the place of words, which are insufficient to convey mechanical ideas in an intelligible manner. General engineering work cannot consist in the production of duplicate pieces, nor in operations performed constantly in the same manner as in ordinary manufacturing; hence there has been much effort expended in adapting machines to general purposes—machines, which seldom avoid the objections of combination, pointed out in a previous chapter. (1.) Describe the different modifications of screw-cutting machines.—(2.) What is gained by revolving the dies instead of the rod?—(3.) What is gained by expanding dies?—(4.) What is the difference between screws cut by chasing and those cut on a screw-cutting machine? Standard gauging implements were introduced about the year 1840, by the celebrated Swiss engineer, John G. Bodmer, a [148]man who for many reasons deserves to be considered as the founder of machine tool manufacture. He not only employed gauges in his works to secure duplicate dimensions, but also invented and put in use many other reforms in manipulation; among these may be mentioned the decimal or metrical division of measures, a system of detail drawings classified by symbols, the mode of calculating wheels by diametric pitch, with many other things which characterise the best modern practice. He rightly decided that they had recalled sending the caretaker on a foolish errand. They must get back and make some explanation or he would suspect them, perhaps report to somebody else. They could not know that he was shivering, crouched down in the last place of Jeff’s own airplane. "Here," protested Gid; "Sargint Klegg told me to stand on the right. You're smaller'n me. Git on the other side." "They need us," Albin said uncertainly. "They can't do without us." She drew her head away almost angrily, and moved to the next pan. "Oh, how can you speak to me so!" she gulped. "And you w?an't, nuther," said Pete, soothing him. "Either you fetch him here or I send fur the police." HoME一级a在线作爱免费观看2017
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