CHAPTER XXXV. MILLING.

Milling relates to metal cutting with serrated rotary¹ cutters, and differs in many respects from either planing or turning. The movement of the cutting edges can be more rapid than with tools which act continuously, because the edges are cooled during the intervals² between each cut; that is, if a milling tool has twenty teeth, any single tooth or edge acts only from a fifteenth to a twentieth part of the time; and as the cutting distance or time of cutting is rarely long enough to generate much heat, the speed of such tools may be one-half greater than for turning, drilling, or planing tools. Another distinction between milling and other tools is the perfect and rigid³ manner in which the cutting edges are supported; they are short and blunt, besides being usually carried on short rigid mandrils. A result of this rigid support of the tools is seen in the length of the cutting edges that can be employed, which are sometimes four inches or more in length. It is true the amount of material cut away in milling is much less than the edge movement will indicate when compared with turning or planing; yet the displacing capacity of a milling machine exceeds that of either a lathe⁴ or a planing machine. Theoretically the cutting or displacing capacity of any metal or wood cutting machine, is as the length of the edges multiplied into the speed of their cutting movement; a rule which applies very uniformly in wood cutting, and also in metal cutting within certain limits; but the strains that arise in metal cutting are so great that they may exceed all means of resisting them either in the material acted upon, or in the means of supporting tools, so that the length of cutting edges is limited. In turning chilled rolls at Pittsburg, [141] tools to six inches wide are employed, and the effect produced is as the length of the edge; but the depth of the cut is slight, and the operation is only possible because of the extreme rigidity⁵ of the pieces turned, and the tools being supported without movable joints⁶ as in common lathes⁷.

Under certain conditions a given quantity of soft iron or steel may be cut away at less expense, and with greater accuracy, by milling than by any other process.

A milling tool with twenty edges should represent as much wearing capacity as a like number of separate tools, and may be said to equal twenty duplicate tools; hence, in cutting grooves⁸, notches⁹, or similar work, a milling tool is equivalent to a large number of duplicate single tools, which cannot be made or set with the same truth; so that milling secures accuracy and duplication, objects which are in many cases more important than speed.

Milling, as explained, being a more rapid process than either planing or turning, it seems strange that so few machines of this kind are employed in engineering shops. This points to some difficulty to be contended with in milling, which is not altogether apparent, because economic reasons would long ago have led to a more extended use of milling processes, if the results were as profitable as the speed of cutting indicates. This is, however, not the case, except on certain kinds of material, and only for certain kinds of work.

The advantages gained by milling, as stated, are speed, duplication, and accuracy; the disadvantages are the expense of preparing tools and their perishability¹⁰.

A solid milling cutter must be an accurately¹¹ finished piece of work, made with more precision than can be expected in the work it is to perform. This accuracy cannot be attained¹² by ordinary processes, because such tools, when tempered, are liable to become distorted in shape, and frequently break. When hardened they must be finished by grinding processes, if intended for any accurate work; in fact, no tools, except gauging¹³ implements¹⁴, involve more expense to prepare, and none are so liable to accident when in use.

Such tools consist of a combination of cutting edges, all of which may be said to depend on each one; because if one breaks, the next in order will have a double duty to perform, and will soon follow—a reversal of the old adage¹⁵, that 'union is strength,' [142] if by strength is meant endurance.

In planing and turning, the tools require no exact form; they can be roughly made, except the edge, and even this, in most cases, is shaped by the eye. Such tools are maintained at a trifling¹⁶ expense, and the destruction of an edge is a matter of no consequence. The form, temper, and strength can be continually adapted to the varying conditions of the work and the hardness of material. The line of division between planing and milling is fixed¹⁷ by two circumstances—the hardness and uniformity of the material to be cut, and the importance of duplication. Brass¹⁸, clean iron, soft steel, or any homogeneous metal not hard enough to cause risk to the tools, can be milled at less expense than planed, provided there is enough work of a uniform character to justify¹⁹ the expense of milling tools. Cutting the teeth of wheels is an example where milling is profitable, but not to the extent generally supposed. In the manufacture of small arms, sewing machines, clocks, and especially watches, where there is a constant and exact duplication of parts, milling is indispensable. Such manufactures are in some cases founded on milling operations, as will be pointed²⁰ out in another chapter.

Milling tools large enough to admit of detachable cutters being employed, are not so expensive to maintain as solid tools. Edge movement can sometimes be multiplied in this way, so as to greatly exceed what a single tool will perform.

Milling tools are employed at Crewe for roughing out the slots in locomotive crank axles. A number of detachable tools are mounted on a strong disc, so that four to six will act at one time; in this way the displacement²¹ exceeds what a lathe can perform when acting²² continuously with two tools. Rotary planing machines constructed on the milling principle, have been tried for plane surfaces, but with indifferent success, except for rough work.

There is nothing in the construction or operation of milling machines but what will be at once understood by a learner who sees them in operation. The whole intricacy of the process lies in its application or economic value, and but very few, even among the most skilled, are able in all cases to decide when milling can be employed to advantage. Theoretical conclusions, aside from practical experience, will lead one to suppose that milling can be applied²³ in nearly all kinds of work, an opinion [143] which has in many cases led to serious mistakes.

(1.) If milling tools operate faster than planing or turning tools, why are they not more employed?—(2.) How may the effect produced by cutting tools generally be computed²⁴?—(3.) To what class of work are milling machines especially suited?—(4.) Why do milling processes produce more accurate dimensions than are attainable²⁵ by turning or planing?—(5.) Why can some branches of manufacture be said to depend on milling processes?

1 rotary   

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。

2 intervals   

n.[军事]间隔( interval的名词复数 )；间隔时间；[数学]区间；（戏剧、电影或音乐会的）幕间休息

参考例句：

• The forecast said there would be sunny intervals and showers. 预报间晴，有阵雨。
• Meetings take place at fortnightly intervals. 每两周开一次会。

3 rigid   

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。

4 lathe   

n.车床，陶器，镟床

参考例句：

• Gradually she learned to operate a lathe.她慢慢地学会了开车床。
• That lathe went out of order at times.那台车床有时发生故障。

5 rigidity   

adj.钢性，坚硬

参考例句：

• The rigidity of the metal caused it to crack.这金属因刚度强而产生裂纹。
• He deplored the rigidity of her views.他痛感她的观点僵化。

6 joints   

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。

7 lathes   

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。

8 grooves   

n.沟( groove的名词复数 )；槽；老一套；（某种）音乐节奏v.沟( groove的第三人称单数 )；槽；老一套；（某种）音乐节奏

参考例句：

• Wheels leave grooves in a dirt road. 车轮在泥路上留下了凹痕。 来自《简明英汉词典》
• Sliding doors move in grooves. 滑动门在槽沟中移动。 来自《现代汉英综合大词典》

9 notches   

n.（边缘或表面上的）V型痕迹( notch的名词复数 )；刻痕；水平；等级

参考例句：

• The Indians cut notches on a stick to keep count of numbers. 印第安人在棒上刻V形凹痕用来计数。 来自《现代英汉综合大词典》
• They cut notches in the handle of their pistol for each man they shot. 他们每杀一个人就在枪托上刻下一个V形记号。 来自辞典例句

10 perishability   

易腐烂性，易朽性

参考例句：

11 accurately   

adv.准确地，精确地

参考例句：

• It is hard to hit the ball accurately.准确地击中球很难。
• Now scientists can forecast the weather accurately.现在科学家们能准确地预报天气。

12 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。

13 gauging   

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

参考例句：

• The method is especially attractive for gauging natural streams. 该方法对于测量天然的流注具有特殊的吸引力。 来自辞典例句
• Incommunicative as he was, some time elapsed before I had an opportunity of gauging his mind. 由于他不爱说话，我过了一些时候才有机会探测他的心灵。 来自辞典例句

14 implements   

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

参考例句：

• Primitive man hunted wild animals with crude stone implements. 原始社会的人用粗糙的石器猎取野兽。 来自《现代汉英综合大词典》
• They ordered quantities of farm implements. 他们订购了大量农具。 来自《现代汉英综合大词典》

15 adage   

n.格言，古训

参考例句：

• But the old adage that men grow into office has not proved true in my experience.但是，根据我的经验，人们所谓的工作岗位造就人材这句古话并不正确。
• Her experience lends credence to the adage " We live and learn!"她的经验印证了一句格言: 活到老，学到老！

16 trifling   

adj.微不足道的；没什么价值的

参考例句：

• They quarreled over a trifling matter.他们为这种微不足道的事情争吵。
• So far Europe has no doubt, gained a real conveniency,though surely a very trifling one.直到现在为止,欧洲无疑地已经获得了实在的便利，不过那确是一种微不足道的便利。

17 fixed   

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。

18 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。

19 justify   

vt.证明…正当(或有理)，为…辩护

参考例句：

• He tried to justify his absence with lame excuses.他想用站不住脚的借口为自己的缺席辩解。
• Can you justify your rude behavior to me?你能向我证明你的粗野行为是有道理的吗？

20 pointed   

adj.尖的，直截了当的

参考例句：

• He gave me a very sharp pointed pencil.他给我一支削得非常尖的铅笔。
• She wished to show Mrs.John Dashwood by this pointed invitation to her brother.她想通过对达茨伍德夫人提出直截了当的邀请向她的哥哥表示出来。

21 displacement   

n.移置，取代，位移，排水量

参考例句：

• They said that time is the feeling of spatial displacement.他们说时间是空间位移的感觉。
• The displacement of all my energy into caring for the baby.我所有精力都放在了照顾宝宝上。

22 acting   

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。

23 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。

24 computed   

adj.[医]计算的，使用计算机的v.计算，估算( compute的过去式和过去分词 )

参考例句：

• He computed that the project would take seven years to complete. 他估计这项计划要花七年才能完成。 来自《简明英汉词典》
• Resolving kernels and standard errors can also be computed for each block. 还可以计算每个块体的分辨核和标准误差。 来自辞典例句

25 attainable   

a.可达到的，可获得的

参考例句：

• They set the limits of performance attainable. 它们确定着可达到的运行限度。
• If objectives are to be meaningful to people, they must be clear, attainable, actionable, and verifiable. 如果目标对人们是具有意义的，则目标必须是清晰的，能达到的，可以行动的，以及可供检验的。