Standard gauging3 implements4 were introduced about the year 1840, by the celebrated6 Swiss engineer, John G. Bodmer, a [148]man who for many reasons deserves to be considered as the founder7 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.
The importance of standard dimensions, and the effect which a system of gauging may have in the construction of machines, will be a matter of some difficulty for a learner to understand. The interchangeability of parts, which is the immediate8 object in employing gauges, is plain enough, and some of the advantages at once apparent, yet the ultimate effects of such a system extend much farther than will at first be supposed.
The division of labour, that system upon which we may say our great industrial interests are founded, is in machine fitting promoted in a wonderful degree by the use of gauging implements. If standard dimensions can be maintained, it is easy to see that the parts of a machine can be constructed by different workmen, or in different shops, and these parts when assembled all fit together, without that tedious and uncertain plan of try-fitting which was once generally practised. There are, it is true, certain kinds of fitting which cannot well be performed by gauges; moving flat surfaces, such as the bearings of lathe9 slides or the faces of steam engine valves, are sooner and better fitted by trying them together and scraping off the points of contact; but even in such cases the character of the work will be improved, if one or both surfaces have been first levelled by gauging or surface plates.
In cylindrical10 fitting, which as before pointed11 out, constitutes the greater part in machine fitting, gauges are especially important, because trial-fitting is in most cases impossible.
Flat or plane joints12 nearly always admit of adjustment between the fitted surfaces; that is, the material scraped or ground away in fitting can be compensated14 by bringing the pieces nearer together; but parallel cylindrical joints cannot even be tried together until finished, consequently, there can be nothing cut away in trying them together. Tapering15, or conical joints, can of course be trial-fitted, and even parallel fits are sometimes made by trial, but it is evident that the only material that can [149] be cut away in such cases, is what makes the difference between a fit too close, and one which will answer in practice.
As to the practical results which may be attained16 by a gauging system, it may be said that they are far in advance of what is popularly supposed, especially in Europe, where gauges were first employed.
The process of milling, which has been so extensively adopted in the manufacture of guns, watches, sewing-machines, and similar work in America, has, on principles explained in the chapter on milling, enabled a system of gauging which it is difficult to comprehend without seeing the processes carried on. And so important is the effect due to this duplicating or gauging system, that several important branches of manufacture have been controlled in this way, when other elements of production, such as the price of labour, rent, interest, and so on, have been greatly in favour of countries where the trying system is practised.
As remarked, the gauging system is particularly adapted to, or enabled by milling processes, and of course must have its greatest effect in branches of work directed to the production of uniform articles, such as clocks, watches, sewing-machines, guns, hand tools, and so on. That is, the direct effect on the cost of processes will be more apparent and easily understood in such branches of manufacture; yet in general engineering work, where each machine is more or less modified, and made to special plans, the commercial gain resulting from the use of gauges is considerable.
In respect to repairing alone, the consideration of having the parts of machinery fitted to standard sizes is often equal to its whole value.
Machinery subjected to destructive wear, and to be operated at a distance from machine shops—locomotive engines for example—if not constructed with standard dimensions, may, by the detention17 due to repairing, cause a loss and inconvenience equal to their value; if a shaft18 wheel bearing, or even a fitted screw bolt is broken, time must be allowed to make the parts new; and in order to fit them, the whole machine, or such of its details as have connection with the broken parts, must be taken to a shop in order to fit by trial.
The duplicate system has gradually made its way in locomotive engineering, and will no doubt extend to the whole of [150] railway equipment, as constants for dimensions are proved and agreed upon.
The gauging system has been no little retarded19 by a selfish and mistaken opinion that an engineering establishment may maintain peculiar20 standards of its own; in fact, relics21 of this spirit are yet to be met with in old machines, where the pitch of screw-threads has been made to fractional parts of an inch, so that engineers, other than the original makers22, could not well perform repairing, or replace broken parts.
One of the effects of employing gauges in machine fitting is to inspire confidence in workmen. Instead of a fit being regarded as a mysterious result more the work of chance than design, men accustomed to gauges come to regard precision as something both attainable23 and indispensable. A learner, after examining a set of well fitted cylindrical gauges, will form a new conception of what a fit is, and will afterwards have a new standard fixed24 in his mind.
The variation of dimensions which are sensible to the touch at one ten-thousandth part of an inch, furnishes an example of how important the human senses are even after the utmost precision attainable by machine action. Pieces may pass beneath the cutters of a milling machine under conditions, which so far as machinery avails will produce uniform sizes, yet there is no assurance of the result until the work is felt by gauges.
The eye fails to detect variations in size, even by comparison, long before we reach the necessary precision in common fitting. Even by comparison with figured scales or measuring with rules, the difference between a proper and a spoiled fit is not discernible by sight.
Many of the most accurate measurements are, however, performed by sight, with vernier calipers25 for example, the variation being multiplied hundreds or thousands of times by mechanism26, until the least differences can be readily seen.
In multiplying the variations of a measuring implement5 by mechanism, it is obvious that movable joints must be employed; it is also obvious that no positive joint13, whether cylindrical or flat, could be so accurately27 fitted as to transmit such slight movement as occurs in gauging or measuring. This difficulty is in most measuring instruments overcome by employing a principle not before alluded28 to, but common in many machines, that of elastic29 [151] compensation.
A pair of spring calipers will illustrate30 this principle. The points are always steady, because the spring acting31 continually in one direction compensates32 the loose play that may be in the screw. In a train of tooth wheels there is always more or less play between the teeth; and unless the wheels always revolve33 in one direction, and have some constant resistance offered to their motion, 'backlash' or irregular movement will take place; but if there is some constant and uniform resistance such as a spring would impart, a train of wheels will transmit the slightest motion throughout.
The extreme nicety with which gauging implements are fitted seems at first thought to be unnecessary, but it must be remembered that a cylindrical joint in ordinary machine fitting involves a precision almost beyond the sense of feeling, and that any sensible variation in turning gauges is enough to spoil a fit.
Opposed to the maintenance of standard dimensions are the variations in size due to temperature. This difficulty applies alike to gauging implements and to parts that are to be tested; yet in this, as in nearly every phenomenon connected with matter, we have succeeded in turning it to some useful purpose. Bands of iron, such as the tires of wheels when heated, can be 'shrunk' on, and a compressive force and security attained, which would be impossible by forcing the parts together both at the same temperature. Shrinking has, however, been almost entirely34 abandoned for such joints as can be accurately fitted.
(1.) How may gauging implements affect the division of labour?—(2.) In what way do standard dimensions affect the value of machinery?—(3.) Why cannot cylindrical joints be fitted by trying them together?—(4.) Under what circumstances is it most important that the parts of machinery should have standard dimensions?—(5.) Which sense is most acute in testing accurate dimensions?—(6.) How may slight variations in dimensions be made apparent to sight?
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1
gauges
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| n.规格( gauge的名词复数 )；厚度；宽度；标准尺寸v.（用仪器）测量( gauge的第三人称单数 )；估计；计量；划分 | |
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machinery
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| n.(总称)机械，机器；机构 | |
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gauging
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| n.测量[试]，测定，计量v.（用仪器）测量( gauge的现在分词 )；估计；计量；划分 | |
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implements
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| n.工具( implement的名词复数 )；家具；手段；[法律]履行（契约等）v.实现( implement的第三人称单数 )；执行；贯彻；使生效 | |
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implement
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| n.(pl.)工具，器具；vt.实行，实施，执行 | |
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celebrated
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| adj.有名的，声誉卓著的 | |
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Founder
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| n.创始者，缔造者 | |
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immediate
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| adj.立即的；直接的，最接近的；紧靠的 | |
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lathe
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| n.车床，陶器，镟床 | |
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cylindrical
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| adj.圆筒形的 | |
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pointed
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| adj.尖的，直截了当的 | |
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joints
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| 接头( joint的名词复数 )； 关节； 公共场所（尤指价格低廉的饮食和娱乐场所） （非正式）； 一块烤肉 （英式英语） | |
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joint
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| adj.联合的，共同的；n.关节，接合处；v.连接，贴合 | |
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compensated
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| 补偿，报酬( compensate的过去式和过去分词 )； 给（某人）赔偿（或赔款） | |
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tapering
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| adj.尖端细的 | |
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attained
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| （通常经过努力）实现( attain的过去式和过去分词 )； 达到； 获得； 达到（某年龄、水平、状况） | |
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detention
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| n.滞留，停留；拘留，扣留；(教育)留下 | |
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shaft
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| n.(工具的)柄，杆状物 | |
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retarded
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| a.智力迟钝的，智力发育迟缓的 | |
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peculiar
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| adj.古怪的，异常的；特殊的，特有的 | |
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relics
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| [pl.］n.遗物，遗迹，遗产；遗体，尸骸 | |
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makers
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| n.制造者，制造商（maker的复数形式） | |
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attainable
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| a.可达到的，可获得的 | |
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fixed
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| adj.固定的，不变的，准备好的；(计算机)固定的 | |
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calipers
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| n.书法，测径器；测径器 | |
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mechanism
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| n.机械装置；机构，结构 | |
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accurately
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| adv.准确地，精确地 | |
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alluded
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| 提及，暗指( allude的过去式和过去分词 ) | |
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elastic
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| n.橡皮圈，松紧带；adj.有弹性的；灵活的 | |
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illustrate
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| v.举例说明，阐明；图解，加插图 | |
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acting
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| n.演戏，行为，假装；adj.代理的，临时的，演出用的 | |
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compensates
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| 补偿，报酬( compensate的第三人称单数 )； 给（某人）赔偿（或赔款） | |
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revolve
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| vi.(使)旋转；循环出现 | |
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entirely
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| ad.全部地，完整地；完全地，彻底地 | |
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