CHAPTER XIII. GEARING AS A MEANS OF TRANSMITTING POWER.

The term gearing, which was once applied¹ to wheels, shafts², and the general mechanism³ of mills and factories, has now in common use become restricted to tooth wheels, and is in this sense employed here. Gearing as a means of transmitting motion is employed when the movement of machines, or the parts of machines, must remain relatively⁴ the same, as in the case of the traversing screw of an engine lathe—when a heavy force is transmitted between shafts that are near to each other, or when shafts to be connected are arranged at angles with each other. This rule is of course not constant, except as to cases where positive relative motion has to be maintained. Noise, and the liability to sudden obstruction⁵, may be reasons for not employing tooth wheels in many cases when the distance between and the position of shafts would render such a connection the most durable⁶ and cheap. Gearing under ordinary strain, within limited speed, and when other conditions admit of its use, is the cheapest and most durable mechanism for transmitting power; but the amount of gearing employed in machinery⁷, especially in Europe, is no doubt far greater than it will be in future, when belts are better understood.

No subject connected with mechanics has been more thoroughly⁸ investigated than that of gearing. Text-books are replete⁹ with every kind of information pertaining¹⁰ to wheels, at least so far as the subject can be made a mathematical one; and to judge from the amount of matter, formul?, and diagrams, relating to the teeth of wheels that an apprentice¹¹ will meet with, he will no doubt be led to believe that the main object of modern engineering is to generate wheels. It must be admitted that the teeth of wheels and the proportions of wheels is a very important matter to understand, and should be studied with the greatest care; but it is equally important to know how to produce the teeth in metal after their configuration¹² has been defined on paper; to understand the endurance of teeth under abrasive¹³ wear when made of wrought¹⁴ or cast iron, brass¹⁵ or steel; how patterns can be constructed from which correct wheels may be cast, and how the teeth of wheels can be cut [52]by machinery, and so on.

A learner should, in fact, consider the application and operative conditions of gearing as one of the main parts of the subject, and the geometry or even the construction of wheels as subsidiary; in this way attention will be directed to that which is most difficult to learn, and a part for which facilities are frequently wanting. Gearing may be classed into five modifications—spur wheels, bevel wheels, tangent wheels, spiral wheels, and chain wheels; the last I include among gearing because the nature of their operation is analogous¹⁶ to tooth wheels, although at first thought chains seem to correspond more to belts than gearing. The motion imparted by chains meshing¹⁷ over the teeth of wheels is positive, and not frictional as with belts; the speed at which such chains may run, with other conditions, correspond to gearing.

Different kinds of gearing can be seen in almost every engineering establishment, and in view of the amount of scientific information available, it will only be necessary to point out some of the conditions that govern the use and operation of the different kinds of wheels. The durability¹⁸ of gearing, aside from breaking, is dependent upon pressure and the amount of rubbing action that takes place between the teeth when in contact. Spur wheels, or bevel wheels, when the pitch is accurate and the teeth of the proper form, if kept clean and lubricated, wear but little, because the contact between the teeth is that of rolling instead of sliding. In many cases, one wheel of a pair is filled with wooden cogs; in this arrangement there are four objects, to avoid noise, to attain¹⁹ a degree of elasticity²⁰ in the teeth, to retain lubricants by absorption in the wood, and to secure by wear a better configuration of the teeth than is usually attained²¹ in casting, or even in cutting teeth.

Tangent wheels and spiral gearing have only what is termed line contact between the bearing surfaces, and as the action between these surfaces is a sliding one, such wheels are subject to rapid wear, and are incapable²² of sustaining much pressure, or transmitting a great amount of power, except the surfaces be hard and lubrication constant. In machinery the use of tangent wheels is mainly to secure a rapid change of speed, usually to diminish motion and increase force.

By placing the axes of tangent gearing so that the threads or teeth of the pinions²³ are parallel to the face of the driven teeth, [53] as in the planing machines of Messrs Wm. Sellers & Co., the conditions of operation are changed, and an interesting problem arises. The progressive or forward movement of the pinion²⁴ teeth may be equal to the sliding movement between the surfaces; and an equally novel result is, that the sliding action is distributed over the whole breadth of the driven teeth.

In spiral gearing the line of force is at an angle of forty-five degrees with the bearing faces of the teeth, and the sliding movement equal to the speed of the wheels at their periphery²⁵; the bearing on the teeth, as before said, is one of line contact only. Such wheels cannot be employed except in cases where an inconsiderable force is to be transmitted. Spiral wheels are employed to connect shafts that cross each other at right angles but in different planes, and when the wheels can be of the same size.

It may be mentioned in regard to rack gearing for communicating movement to the carriages of planing machines or other purposes of a similar nature: the rack can be drawn²⁶ to the wheel, and a lifting action avoided, by shortening the pitch of the rack, so that it will vary a little from the driving wheel. The rising or entering teeth in this case do not come in contact with those on the rack until they have attained a position normal to the line of the carriage movement.

(1.) Into what classes can gearing be divided?—(2.) What determines the wearing capacity of gearing?—(3.) What is the advantage gained by employing wooden cogs for gear wheels?—(4.) Why are tangent or worm wheels not durable?

1 applied   

adj.应用的；v.应用，适用

参考例句：

• She plans to take a course in applied linguistics.她打算学习应用语言学课程。
• This cream is best applied to the face at night.这种乳霜最好晚上擦脸用。

2 shafts   

n.轴( shaft的名词复数 )；（箭、高尔夫球棒等的）杆；通风井；一阵（疼痛、害怕等）

参考例句：

• He deliberately jerked the shafts to rock him a bit. 他故意的上下颠动车把，摇这个老猴子几下。 来自汉英文学 - 骆驼祥子
• Shafts were sunk, with tunnels dug laterally. 竖井已经打下，并且挖有横向矿道。 来自辞典例句

3 mechanism   

n.机械装置；机构，结构

参考例句：

• The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
• The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。

4 relatively   

adv.比较...地，相对地

参考例句：

• The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
• The operation was relatively painless.手术相对来说不痛。

5 obstruction   

n.阻塞，堵塞；障碍物

参考例句：

• She was charged with obstruction of a police officer in the execution of his duty.她被指控妨碍警察执行任务。
• The road was cleared from obstruction.那条路已被清除了障碍。

6 durable   

adj.持久的，耐久的

参考例句：

• This raincoat is made of very durable material.这件雨衣是用非常耐用的料子做的。
• They frequently require more major durable purchases.他们经常需要购买耐用消费品。

7 machinery   

n.(总称)机械，机器；机构

参考例句：

• Has the machinery been put up ready for the broadcast?广播器材安装完毕了吗？
• Machinery ought to be well maintained all the time.机器应该随时注意维护。

8 thoroughly   

adv.完全地，彻底地，十足地

参考例句：

• The soil must be thoroughly turned over before planting.一定要先把土地深翻一遍再下种。
• The soldiers have been thoroughly instructed in the care of their weapons.士兵们都系统地接受过保护武器的训练。

9 replete   

adj.饱满的，塞满的；n.贮蜜蚁

参考例句：

• He was replete with food and drink.他吃喝得饱饱的。
• This immense space may be replete with happiness and glory.这巨大的空间可能充满了幸福和光荣。

10 pertaining   

与…有关系的，附属…的，为…固有的(to)

参考例句：

• Living conditions are vastly different from those pertaining in their country of origin. 生活条件与他们祖国大不相同。
• The inspector was interested in everything pertaining to the school. 视察员对有关学校的一切都感兴趣。

11 apprentice   

n.学徒，徒弟

参考例句：

• My son is an apprentice in a furniture maker's workshop.我的儿子在一家家具厂做学徒。
• The apprentice is not yet out of his time.这徒工还没有出徒。

12 configuration   

n.结构，布局，形态，(计算机)配置

参考例句：

• Geographers study the configuration of the mountains.地理学家研究山脉的地形轮廓。
• Prices range from $119 to $199,depending on the particular configuration.价格因具体配置而异，从119美元至199美元不等。

13 abrasive   

adj.使表面磨损的；粗糙的；恼人的

参考例句：

• His abrasive manner has won him an unenviable notoriety.他生硬粗暴的态度让他声名狼藉。
• She had abrasions to her wrists where the abrasive rope had scraped her.她的手腕有多出磨伤，那是被粗糙的绳子擦伤的。

14 wrought   

v.引起；以…原料制作；运转；adj.制造的

参考例句：

• Events in Paris wrought a change in British opinion towards France and Germany.巴黎发生的事件改变了英国对法国和德国的看法。
• It's a walking stick with a gold head wrought in the form of a flower.那是一个金质花形包头的拐杖。

15 brass   

n.黄铜；黄铜器，铜管乐器

参考例句：

• Many of the workers play in the factory's brass band.许多工人都在工厂铜管乐队中演奏。
• Brass is formed by the fusion of copper and zinc.黄铜是通过铜和锌的熔合而成的。

16 analogous   

adj.相似的；类似的

参考例句：

• The two situations are roughly analogous.两种情況大致相似。
• The company is in a position closely analogous to that of its main rival.该公司与主要竞争对手的处境极为相似。

17 meshing   

结网，啮合

参考例句：

• The modification of gear is a principal method for improving performance meshing. 齿面修形是提高齿轮副啮合性能的重要手段。
• Exact modeling of gear teeth is based on meshing theory. 摘要根据齿轮啮合原理，建立了轮齿的精确齿形。

18 durability   

n.经久性，耐用性

参考例句：

• Nylons have the virtue of durability.尼龙丝袜有耐穿的优点。

19 attain   

vt.达到，获得，完成

参考例句：

• I used the scientific method to attain this end. 我用科学的方法来达到这一目的。
• His painstaking to attain his goal in life is praiseworthy. 他为实现人生目标所下的苦功是值得称赞的。

20 elasticity   

n.弹性，伸缩力

参考例句：

• The skin eventually loses its elasticity.皮肤最终会失去弹性。
• Every sort of spring has a definite elasticity.每一种弹簧都有一定的弹性。

21 attained   

（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）

参考例句：

• She has attained the degree of Master of Arts. 她已获得文学硕士学位。
• Lu Hsun attained a high position in the republic of letters. 鲁迅在文坛上获得崇高的地位。

22 incapable   

adj.无能力的，不能做某事的

参考例句：

• He would be incapable of committing such a cruel deed.他不会做出这么残忍的事。
• Computers are incapable of creative thought.计算机不会创造性地思维。

23 pinions   

v.抓住[捆住]（双臂）( pinion的第三人称单数 )

参考例句：

• These four pinions act as bridges between the side gears. 这四组小齿轮起到连接侧方齿轮组的桥梁作用。 来自互联网
• Tough the sword hidden among pinions may wound you. 虽然那藏在羽翼中间的剑刃也许会伤毁你们。 来自互联网

24 pinion   

v.束缚；n.小齿轮

参考例句：

• At nine the next morning Bentley was pinioned,hooded and hanged.次日上午9点，本特里被捆住双臂，戴上头罩，然后绞死了。
• Why don't you try tightening the pinion nut first?你为什么不先扭紧小齿轮的螺帽？

25 periphery   

n.(圆体的)外面；周围

参考例句：

• Geographically, the UK is on the periphery of Europe.从地理位置上讲，英国处于欧洲边缘。
• The periphery of the retina is very sensitive to motion.视网膜的外围对运动非常敏感。

26 drawn   

v.拖，拉，拔出；adj.憔悴的，紧张的

参考例句：

• All the characters in the story are drawn from life.故事中的所有人物都取材于生活。
• Her gaze was drawn irresistibly to the scene outside.她的目光禁不住被外面的风景所吸引。