时间：<2020-07-07 22:37:38 作者：2O西安seo135 浏览量：9777
Finally, it must constantly be borne in mind that what will be learned is no less a question of faculties than effort, and that the means of succeeding are closed to none who at the beginning form proper plans, and follow them persistently.
If the steam-engine, for instance, had forty years ago been brought to such a state of improvement as to be constructed with standard proportions and arrangement for stationary purposes, all the rules, constants, and data of whatever kind that had been collected and proved, would have been but of little use in adapting steam-engines to railways and the purposes of navigation.Boring, as distinguished from drilling, consists in turning out annular holes to true dimensions, while the term drilling is applied to perforating or sinking holes in solid material. In boring, tools are guided by axial support independent of the  bearing of their edges on the material, while in drilling, the cutting edges are guided and supported mainly from their contact with and bearing on the material drilled.
A peculiarity of forging is that it is a kind of hand process, where the judgment must continually direct the operations, one blow determining the next, and while pieces forged may be duplicates, there is a lack of uniformity in the manner of producing them. Pieces may be shaped at a white welding heat or at a low red heat, by one or two strong blows or by a dozen lighter blows, the whole being governed by the circumstances of the work as it progresses. A smith may not throughout a whole day repeat an operation precisely in the same manner, nor can he, at the beginning of an operation, tell the length of time required to execute it, nor even the precise manner in which he will perform it. Such conditions are peculiar, and apply to forging alone.
To this classification may be added combination wheels, acting partly by the gravity and partly by the percussion force of the water, by impact combined with reaction, or by impact and maintained pressure.A gain from learning practical fitting is the confidence which such knowledge inspires in either the direction of work or the preparation of plans for machinery. An engineer who hesitates in his plans for fear of criticism, or who does not feel a perfect confidence in them, will never achieve much success.This principle is somewhat obscure, and the nature of percussive forces not generally considered—a matter which may be illustrated by considering the action of a simple hand-hammer. Few  people, in witnessing the use of a hammer, or in using one themselves, ever think of it as an engine giving out tons of force, concentrating and applying power by functions which, if performed by other mechanism, would involve trains of gearing, levers, or screws; and that such mechanism, if employed instead of a hammer, must lack that important function of applying force in any direction as the will and hands may direct. A simple hand-hammer is in the abstract one of the most intricate of mechanical agents—that is, its action is more difficult to analyse than that of many complex machines involving trains of mechanism; yet our familiarity with hammers causes this fact to be overlooked, and the hammer has even been denied a place among those mechanical contrivances to which there has been applied the name of "mechanical powers."
In conclusion, I will say on the subject of patterns and castings, that a learner must depend mainly upon what he can see and what is explained to him in the pattern-shop and foundry. He need never fear an uncivil answer to a proper question, applied at the right time and place. Mechanics who have enough knowledge to give useful information of their business, have invariably the courtesy and good sense to impart such information to those who require it.
This last sentence brings the matter into a tangible form, and indicates what the subject of gain should have to do with what an apprentice learns of machine construction. Success in an engineering enterprise may be temporarily achieved by illegitimate means—such as misrepresentation of the capacity and quality of what is produced, the use of cheap or improper material, or by copying the plans of others to avoid the expense of engineering service—but in the end the permanent success of an engineering business must rest upon the knowledge and skill that is connected with it.
CHAPTER XX. GENERALISATION OF SHOP PROCESSES.
The first of these operations includes all threading processes performed on lathes, whether with a single tool, by dies carried positively by slide rests, or by milling.In regard to premiums, it is a matter to be determined by the facilities that a work may afford for teaching apprentices. To include experience in all the departments of an engineering establishment, within a reasonable term, none but those of unusual ability can make their services of sufficient value to offset what they receive; and there is no doubt but that premium engagements, when the amount of the premium is based upon the facilities afforded for learning, are fair and equitable.