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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.��No,�� Dick agreed, seeing no fun in the situation for once. ��See! There is a motor connected to a big drum up in the top of the hangar, and the door is counterbalanced so that turning the drum winds up the cable that pulls it up. I suppose the motor reverses to run it down and������<000005>