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首页 » 经典英文小说 » The Economy of Workshop Mainipulation » CHAPTER XXXI. PLANING OR RECIPROCATING MACHINES.
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CHAPTER XXXI. PLANING OR RECIPROCATING MACHINES.
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The term planing should properly be applied1 only to machines that produce planes or flat surfaces, but the technical use of the term includes all cutting performed in right lines, or by what may be called a straight movement of tools.

As no motion except rotary2 can be continuous, and as rotary movement of tools is almost exclusively confined to shaping cylindrical3 pieces, a proper distinction between machine tools which operate in straight lines, and those which operate with circular movement, will be to call them by the names of rotary and reciprocating4.

It may be noticed that all machines, except milling machines, which act in straight lines and produce plane surfaces have reciprocating movement; the class includes planing, slotting and shaping machines; these, with lathes5, constitute nearly the whole equipment of an ordinary fitting shop.

It is strange, considering the simplicity6 of construction and the very important office filled by machines for cutting on plane surfaces, that they were not sooner invented and applied in metal work. Many men yet working at finishing, can remember when all flat surfaces were chipped and filed, and that long after engine lathes had reached a state of efficiency and were generally employed, planing machines were not known. This is no doubt to be accounted for in the fact that reciprocal movement, except that produced by cranks or eccentrics, was unknown or regarded as impracticable for useful purposes until late years, and when finally applied it was thought impracticable to have such movements operate automatically. This may seem quite absurd to even an apprentice7 of the present time, yet such reciprocating movement, as a mechanical problem, is by no means so simple as it may at first appear.

[129]

A planing machine platen, for instance, moves at a uniform rate of speed each way, and by its own motion shifts or reverses the driving power at each extreme of the stroke. Presuming that there were no examples to be examined, an apprentice would find many easier problems to explain than how a planing machine can shift its own belts. If a platen or table disengages the power that is moving it, the platen stops; if the momentum8 carries it enough farther to engage or connect other mechanism9 to drive the platen in the opposite direction, the moment such mechanism comes into gear the platen must stop, and no movement can take place to completely engage clutches or shift belts. This is a curious problem that will be referred to again.

Reciprocating tools are divided into those wherein the cutting movement is given to the tools, as in shaping and slotting machines, and machines wherein the cutting movement is given to the material to be planed, as in a common planing machine. Very strangely we find in general practice that machine tools for both the heaviest and the lightest class of work, such as shaping, and butting10, operate upon the first principle, while pieces of a medium size are generally planed by being moved in contact with stationary11 tools.

This problem of whether to move the material or to move the tools in planing, is an old one; both opinion and practice vary to some extent, yet practice is fast settling down into constant rules.

Judged upon theoretical grounds, and leaving out the mechanical conditions of operation, it would at once be conceded that a proper plan would be to move the lightest body; that is, if the tools and their attachments13 were heavier than the material to be acted upon, then the material should be moved for the cutting action, and vice14 versa. But in practice there are other conditions to be considered more important than a question of the relative weight of reciprocating parts; and it must be remembered that in solving any problem pertaining15 to machine action, the conditions of operation are to be considered first and have precedence over problems of strain, arrangement, or even the general principles of construction; that is, the conditions of operating must form a base from which proportions, arrangements, and so on, must be deduced. A standard planing machine, such as is employed for most kinds of work, is arranged with a running platen or carriage upon which the material is fastened and traversed beneath the cutting tools. [130] The uniformity of arrangement and design in machines of this kind in all countries wherever they are made, must lead to the conclusion that there are substantial reasons for employing running platens instead of giving a cutting movement to the tools.

A planing machine with a running platen occupies nearly twice as much floor space, and requires a frame at least one-third longer than if the platen were fixed16 and the tools performed the cutting movement. The weight which has to be traversed, including the carriage, will in nearly all cases exceed what it would be with a tool movement; so that there must exist some very strong reasons in favour of a moving platen, which I will now attempt to explain, or at least point out some of the more prominent causes which have led to the common arrangement of planing machines.

Strains caused by cutting action, in planing or other machines, fall within and are resisted by the framing; even when the tools are supported by one frame and the material by another, such frames have to be connected by means of foundations which become a constituent17 part of the framing in such cases.

Direct action and reaction are equal; if a force is exerted in any direction there must be an equal force acting18 in the opposite direction; a machine must absorb its own strains.

Keeping this in view, and referring to an ordinary planing machine with which the reader is presumed to be familiar, the focal point of the cutting strain is at the edge of the tools, and radiates from this point as from a centre to the various parts of the machine frame, and through the joints19 fixed and movable between the tools and the frame; to follow back from this cutting point through the mechanism to the frame proper; first starting with the tool and its supports and going to the main frame; then starting from the material to be planed, and following back in the other direction, until we reach the point where the strains are absorbed by the main frame, examining the joints which intervene in the two cases, there will appear some reasons for running carriages.

Beginning at the tool there is, first, a clamped joint20 between the tool and the swing block; second, a movable pivoted21 joint between the block and shoe piece; third, a clamped joint between the shoe piece and the front saddle; fourth, a moving joint [131] where the front saddle is gibed22 to the swing or quadrant plate; fifth, a clamp joint between the quadrant plate and the main saddle; sixth, a moving joint between the main saddle and the cross head; seventh, a clamp joint between the cross head and standards; and eighth, bolted joints between the standards and the main frame; making in all eight distinct joints between the tool and the frame proper, three moving, four clamped, and one bolted joint.

Starting again from the cutting point, and going the other way from the tool to the frame, there is, first, a clamped and stayed joint between the material and platen, next, a running joint between the platen and frame; this is all; one joint that is firm beyond any chance of movement, and a moving joint that is not held by adjustable23 gibs, but by gravity; a force which acts equally at all times, and is the most reliable means of maintaining a steady contact between moving parts.

Reviewing these mechanical conditions, we may at once see sufficient reasons for the platen movement of planing machines; and that it would be objectionable, if not impossible, to add a traversing or cutting action to tools already supported through the medium of eight joints. To traverse for cutting would require a moving gib joint in place of the bolted one, between the standards and main frame, leading to a complication of joints and movements quite impracticable.

These are, however, not the only reasons which have led to a running platen for planing machines, although they are the most important.

If a cutting movement were performed by the tool supports, it would necessarily follow that the larger a piece to be planed, and the greater the distance from the platen to the cutting point, the farther a tool must be from its supports; a reversal of the conditions required; because the heavier the work the greater the cutting strain will be, and the tool supports less able to withstand the strains to be resisted.

It may be assumed that the same conditions apply to the standards of a common planing machine, but the case is different; the upright framing is easily made strong enough by increasing its depth; but the strain upon running joints is as the distance from them at which a force is applied, or to employ a technical phrase, as the amount of overhang. With a moving platen the larger and heavier a piece to be planed, the more [132] firmly a platen is held down; and as the cross section of pieces usually increases with their depth, the result is that a planing machine properly constructed will act nearly as well on thick as thin pieces.

The lifting strain at the front end of a platen is of course increased as the height at which the cutting is done above its top, but this has not in practice been found a difficulty of any importance, and has not even required extra length or weight of platens beyond what is demanded to receive pieces to be planed and to resist flexion in fastening heavy work. The reversing movement of planing machine platens already alluded24 to is one of the most complex problems in machine tool movement.

Platens as a rule run back at twice the forward or cutting movement, and as the motion is uniform throughout each stroke, it requires to be stopped at the extremes by meeting some elastic25 or yielding resistance which, to use a steam phrase, "cushions" or absorbs the momentum, and starts the platen back for the return stroke.

This object is attained26 in planing machines by the friction27 of the belts, which not only cushions the platen like a spring, but in being shifted opposes a gradually increasing resistance until the momentum is overcome and the motion reversed. By multiplying the movement of the platen with levers or other mechanism, and by reason of the movement that is attained by momentum after the driving power ceases to act, it is found practicable to have a platen 'shift its own belts,' a result that would never have been reached by theoretical deductions28, and was no doubt discovered by experiment, like the automatic movement of engine valves is said to have been.

It is not intended to claim that this platen-reversing motion cannot, like any other mechanical movement, be resolved mathematically, but that the mechanical conditions are so obscure and the invention made at a time that warrants the supposition of accidental discovery.

In the driving gearing of planing machines, conditions which favour the reversing movement are high speed and narrow driving belts. The time in which belts may be shifted is as their speed and width; to be shifted a belt must be deflected30 or bent31 edgewise, and from this cause wind spirally in order to pass from one pulley to another. To bend or deflect29 a belt edgewise there will be required a force in proportion to its width, and [133] the time of passing from one pulley to another is as the number of revolutions made by the pulleys.

Planing machines of the most improved construction are driven by two belts instead of one, and many mechanical expedients32 have been adopted to move the belts differentially, so that both should not be on the driving pulley at the same time, but move one before the other in alternate order. This is easily attained by simply arranging the two belts with the distance between them equal to one and one-half or one and three-fourth times the width of the driving pulley. The effect is the same as that accomplished33 by differential shifting gearing, with the advantage of permitting an adjustment of the relative movement of the belts.

Another principle in planing machines which deserves notice is the manner of driving carriages or platens; this is usually performed by means of spur wheels and a rack. A rack movement is smooth enough, and effective enough so far as a mechanical connection between the driving gearing and a platen, but there is a difficulty met with from the torsion and elasticity34 of cross-shafts and a train of reducing gearing. In all other machines for metal cutting, it has been a studied object to have the supports for both the tools and the material as rigid36 as possible; but in the common type of planing machines, such as have rack and pinion12 movement, there is a controversion of this principle, inasmuch as a train of wheels and several cross-shafts constitute a very effective spring between the driving power and the point of cutting, a matter that is easily proved by planing across the teeth of a rack, or the threads of a screw, on a machine arranged with spur wheels and the ordinary reducing gearing. It is true the inertia37 of a platen is interposed and in a measure overcomes this elasticity, but in no degree that amounts to a remedy.

A planing machine invented by Mr Bodmer in 1841, and since improved by Mr William Sellers of Philadelphia, is free from this elastic action of the platen, which is moved by a tangent wheel or screw pinion. In Bodmer's machine the shaft35 carrying the pinion was parallel to the platen, but in Sellers' machine is set on a shaft with its axis38 diagonal to the line of the platen movement, so that the teeth or threads of the pinion act partly by a screw motion, and partly by a progressive forward movement like the teeth of wheels. The rack on the platen of Mr Sellers' [134] machine is arranged with its teeth at a proper angle to balance the friction arising from the rubbing action of the pinion, which angle has been demonstrated as correct at 5°, the ordinary coefficient of friction; as the pinion-shaft is strongly supported at each side of the pinion, and the thrust of the cutting force falls mainly in the line of the pinion shaft, there is but little if any elasticity, so that the motion is positive and smooth.

The gearing of these machines is alluded to here mainly for the purpose of calling attention to what constitutes a new and singular mechanical movement, one that will furnish a most interesting study, and deserves a more extended application in producing slow reciprocating motion.

(1.) Can the driving power be employed directly to shift the belts of a planing machine?—(2.) Why are planing machines generally constructed with a running carriage instead of running tools?—(3.) What objection exists in employing a train of spur wheels to drive a planing machine carriage?—(4.) What is gained by shifting the belts of a planing machine differentially?—(5.) What produces the screeching39 of belts so common with planing machines?—(6.) What conditions favour the shifting of planing machine belts?

点击收听单词发音收听单词发音  

1 applied Tz2zXA     
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 rotary fXsxE     
adj.(运动等)旋转的;轮转的;转动的
参考例句:
  • The central unit is a rotary drum.核心设备是一个旋转的滚筒。
  • A rotary table helps to optimize the beam incidence angle.一张旋转的桌子有助于将光线影响之方式角最佳化。
3 cylindrical CnMza     
adj.圆筒形的
参考例句:
  • huge cylindrical gas tanks 巨大的圆柱形贮气罐
  • Beer cans are cylindrical. 啤酒罐子是圆筒形的。
4 reciprocating 2c7af54cfa9659c75889d0467abecb1f     
adj.往复的;来回的;交替的;摆动的v.报答,酬答( reciprocate的现在分词 );(机器的部件)直线往复运动
参考例句:
  • Dynamic loading is produced by seismic forces, non-steady wind, blast, reciprocating machinery. 动荷载是由于地震力、不稳定的风、冲击波,往复式机器所产生。 来自辞典例句
  • The prime mover may be a gas reciprocating engine. 原动机可能是燃气往复式发动机。 来自辞典例句
5 lathes cd4be0c134cfc2d344542ceda5ac462c     
车床( lathe的名词复数 )
参考例句:
  • They showed keen interest in the various lathes on exhibition. 他们对展出中的各类车床表现出了浓厚的兴趣。
  • To automate the control process of the lathes has become very easy today. 使机床的控制过程自动化现已变得很容易了。
6 simplicity Vryyv     
n.简单,简易;朴素;直率,单纯
参考例句:
  • She dressed with elegant simplicity.她穿着朴素高雅。
  • The beauty of this plan is its simplicity.简明扼要是这个计划的一大特点。
7 apprentice 0vFzq     
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。
8 momentum DjZy8     
n.动力,冲力,势头;动量
参考例句:
  • We exploit the energy and momentum conservation laws in this way.我们就是这样利用能量和动量守恒定律的。
  • The law of momentum conservation could supplant Newton's third law.动量守恒定律可以取代牛顿第三定律。
9 mechanism zCWxr     
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。
10 butting 040c106d50d62fd82f9f4419ebe99980     
用头撞人(犯规动作)
参考例句:
  • When they were talking Mary kept butting in. 当他们在谈话时,玛丽老是插嘴。
  • A couple of goats are butting each other. 两只山羊在用角互相顶撞。
11 stationary CuAwc     
adj.固定的,静止不动的
参考例句:
  • A stationary object is easy to be aimed at.一个静止不动的物体是容易瞄准的。
  • Wait until the bus is stationary before you get off.你要等公共汽车停稳了再下车。
12 pinion 6Syze     
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?
13 attachments da2fd5324f611f2b1d8b4fef9ae3179e     
n.(用电子邮件发送的)附件( attachment的名词复数 );附着;连接;附属物
参考例句:
  • The vacuum cleaner has four different attachments. 吸尘器有四个不同的附件。
  • It's an electric drill with a range of different attachments. 这是一个带有各种配件的电钻。
14 vice NU0zQ     
n.坏事;恶习;[pl.]台钳,老虎钳;adj.副的
参考例句:
  • He guarded himself against vice.他避免染上坏习惯。
  • They are sunk in the depth of vice.他们堕入了罪恶的深渊。
15 pertaining d922913cc247e3b4138741a43c1ceeb2     
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。
16 fixed JsKzzj     
adj.固定的,不变的,准备好的;(计算机)固定的
参考例句:
  • Have you two fixed on a date for the wedding yet?你们俩选定婚期了吗?
  • Once the aim is fixed,we should not change it arbitrarily.目标一旦确定,我们就不应该随意改变。
17 constituent bpxzK     
n.选民;成分,组分;adj.组成的,构成的
参考例句:
  • Sugar is the main constituent of candy.食糖是糖果的主要成分。
  • Fibre is a natural constituent of a healthy diet.纤维是健康饮食的天然组成部分。
18 acting czRzoc     
n.演戏,行为,假装;adj.代理的,临时的,演出用的
参考例句:
  • Ignore her,she's just acting.别理她,她只是假装的。
  • During the seventies,her acting career was in eclipse.在七十年代,她的表演生涯黯然失色。
19 joints d97dcffd67eca7255ca514e4084b746e     
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)
参考例句:
  • Expansion joints of various kinds are fitted on gas mains. 各种各样的伸缩接头被安装在煤气的总管道上了。
  • Expansion joints of various kinds are fitted on steam pipes. 各种各样的伸缩接头被安装在蒸气管道上了。
20 joint m3lx4     
adj.联合的,共同的;n.关节,接合处;v.连接,贴合
参考例句:
  • I had a bad fall,which put my shoulder out of joint.我重重地摔了一跤,肩膀脫臼了。
  • We wrote a letter in joint names.我们联名写了封信。
21 pivoted da69736312dbdb6475d7ba458b0076c1     
adj.转动的,回转的,装在枢轴上的v.(似)在枢轴上转动( pivot的过去式和过去分词 );把…放在枢轴上;以…为核心,围绕(主旨)展开
参考例句:
  • His old legs and shoulders pivoted with the swinging of the pulling. 他一把把地拉着,两条老迈的腿儿和肩膀跟着转动。 来自英汉文学 - 老人与海
  • When air is moving, the metal is pivoted on the hinge. 当空气流动时,金属板在铰链上转动。 来自辞典例句
22 gibed 83958b701eaaa0d09f19f81999274a8f     
v.嘲笑,嘲弄( gibe的过去式和过去分词 )
参考例句:
  • One of the other officers at the table gibed. 桌上有个军官挖苦他。 来自辞典例句
  • They gibed at my mistakes. 他们嘲笑我的错误。 来自辞典例句
23 adjustable vzOzkc     
adj.可调整的,可校准的
参考例句:
  • More expensive cameras have adjustable focusing.比较贵的照相机有可调焦距。
  • The chair has the virtue of being adjustable.这种椅子具有可调节的优点。
24 alluded 69f7a8b0f2e374aaf5d0965af46948e7     
提及,暗指( allude的过去式和过去分词 )
参考例句:
  • In your remarks you alluded to a certain sinister design. 在你的谈话中,你提到了某个阴谋。
  • She also alluded to her rival's past marital troubles. 她还影射了对手过去的婚姻问题。
25 elastic Tjbzq     
n.橡皮圈,松紧带;adj.有弹性的;灵活的
参考例句:
  • Rubber is an elastic material.橡胶是一种弹性材料。
  • These regulations are elastic.这些规定是有弹性的。
26 attained 1f2c1bee274e81555decf78fe9b16b2f     
(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。
27 friction JQMzr     
n.摩擦,摩擦力
参考例句:
  • When Joan returned to work,the friction between them increased.琼回来工作后,他们之间的摩擦加剧了。
  • Friction acts on moving bodies and brings them to a stop.摩擦力作用于运动着的物体,并使其停止。
28 deductions efdb24c54db0a56d702d92a7f902dd1f     
扣除( deduction的名词复数 ); 结论; 扣除的量; 推演
参考例句:
  • Many of the older officers trusted agents sightings more than cryptanalysts'deductions. 许多年纪比较大的军官往往相信特务的发现,而不怎么相信密码分析员的推断。
  • You know how you rush at things,jump to conclusions without proper deductions. 你知道你处理问题是多么仓促,毫无合适的演绎就仓促下结论。
29 deflect RxvxG     
v.(使)偏斜,(使)偏离,(使)转向
参考例句:
  • Never let a little problem deflect you.决不要因一点小问题就半途而废。
  • They decided to deflect from the original plan.他们决定改变原计划。
30 deflected 3ff217d1b7afea5ab74330437461da11     
偏离的
参考例句:
  • The ball deflected off Reid's body into the goal. 球打在里德身上反弹进球门。
  • Most of its particles are deflected. 此物质的料子大多是偏斜的。
31 bent QQ8yD     
n.爱好,癖好;adj.弯的;决心的,一心的
参考例句:
  • He was fully bent upon the project.他一心扑在这项计划上。
  • We bent over backward to help them.我们尽了最大努力帮助他们。
32 expedients c0523c0c941d2ed10c86887a57ac874f     
n.应急有效的,权宜之计的( expedient的名词复数 )
参考例句:
  • He is full of [fruitful in] expedients. 他办法多。 来自《现代英汉综合大词典》
  • Perhaps Calonne might return too, with fresh financial expedients. 或许卡洛纳也会回来,带有新的财政机谋。 来自辞典例句
33 accomplished UzwztZ     
adj.有才艺的;有造诣的;达到了的
参考例句:
  • Thanks to your help,we accomplished the task ahead of schedule.亏得你们帮忙,我们才提前完成了任务。
  • Removal of excess heat is accomplished by means of a radiator.通过散热器完成多余热量的排出。
34 elasticity 8jlzp     
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。
35 shaft YEtzp     
n.(工具的)柄,杆状物
参考例句:
  • He was wounded by a shaft.他被箭击中受伤。
  • This is the shaft of a steam engine.这是一个蒸汽机主轴。
36 rigid jDPyf     
adj.严格的,死板的;刚硬的,僵硬的
参考例句:
  • She became as rigid as adamant.她变得如顽石般的固执。
  • The examination was so rigid that nearly all aspirants were ruled out.考试很严,几乎所有的考生都被淘汰了。
37 inertia sbGzg     
adj.惰性,惯性,懒惰,迟钝
参考例句:
  • We had a feeling of inertia in the afternoon.下午我们感觉很懒。
  • Inertia carried the plane onto the ground.飞机靠惯性着陆。
38 axis sdXyz     
n.轴,轴线,中心线;坐标轴,基准线
参考例句:
  • The earth's axis is the line between the North and South Poles.地轴是南北极之间的线。
  • The axis of a circle is its diameter.圆的轴线是其直径。
39 screeching 8bf34b298a2d512e9b6787a29dc6c5f0     
v.发出尖叫声( screech的现在分词 );发出粗而刺耳的声音;高叫
参考例句:
  • Monkeys were screeching in the trees. 猴子在树上吱吱地叫着。
  • the unedifying sight of the two party leaders screeching at each other 两党党魁狺狺对吠的讨厌情景


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