【正文】 uipment rather than spend more effort in trying to improve the process. 如果隨機(jī)原因?qū)Τ叽缱兓挠绊戇^(guò)大，一般來(lái)說(shuō)采用更精密的加工設(shè)備，要比花費(fèi)更多精力來(lái)改變生產(chǎn)過(guò)程更為有效Lesson29 The technique of dimensioning parts within a require range of variation to ensure interchangeability is called tolerancing. Each dimension is allowed a certain degree of variation within a specified zone ,or tolerance .for example, a part^s dimension might be expressed as 20+,which allows a tolerance (variation in size ) of mm.給零件標(biāo)注尺寸使其在一個(gè)規(guī)定的區(qū)間內(nèi)變動(dòng)，以保證他們具有互換性的技術(shù)稱為公差技術(shù)。公差的大小是由設(shè)計(jì)人員所確定的，它取決于許多與設(shè)計(jì)有關(guān)的條件以及過(guò)去在設(shè)計(jì)類似產(chǎn)品時(shí)所獲得的經(jīng)驗(yàn)（如果有這方面經(jīng)驗(yàn)的話）。在第一次制圖之后，任何為了改進(jìn)設(shè)計(jì)方案而作的修改和更正都應(yīng)該在修改欄中標(biāo)明。Title Blocks In practice, title blocks usually contain the title or part name, drafter, date, scale, pany, and sheet number. Other information, such as tolerances, checkers, and materials, also may be given. Any modifications or changes added after the first version to improve the design is shown in the revision blocks. 標(biāo)題欄 在實(shí)踐中，標(biāo)題欄中通常包括標(biāo)題或零件名稱、制圖員、日期、比例、公司和圖號(hào)。所有的正投影原理和繪圖技術(shù)都可以用來(lái)在工作圖中表達(dá)一個(gè)項(xiàng)目中的細(xì)節(jié)。經(jīng)驗(yàn)表明，可以采用某些便宜材料作為代替。在概念設(shè)計(jì)階段，設(shè)計(jì)者著重考慮產(chǎn)品應(yīng)該具有的功能。 (c) production design. During the conceptualdesign stage, the designer is concerned primarily with the functions the product is to fulfill. 制造任何產(chǎn)品的第一步工作都是設(shè)計(jì)。Lesson17The first step in the manufacture of any product is design, which usually takes place in several distinct stages: (a) conceptual。這表明由于硬度是非破壞性試驗(yàn)，而且不需要專門的試件，因而硬度是一個(gè)容易測(cè)量的性能。Most hardnesstesting systems employ a standard load which is applied to a ball or pyramid in contact with the material to be tested. The hardness is then expressed as a function of the size of the resulting indentation. This means that hardness is an easy property to measure, because the test is nondestructive and test specimens are not required. Usually the test can be conducted directly on an actual machine element.大多數(shù)硬度試驗(yàn)系統(tǒng)是將一個(gè)標(biāo)準(zhǔn)的載荷加在與被試驗(yàn)材料相接觸的小球或者棱錐上。Ideally, in designing any machine element, the engineer should have at his disposal the results of a great many strength tests of the particular material chosen. These tests should have been made on specimens having the same heat treatment, surface roughness, and size as the element he proposes to design, and the tests should be made under exactly the same loading conditions as the part will experience in service.設(shè)計(jì)任何機(jī)械零件的理想情況為，工程師可以利用大量的他所選用的這種材料的強(qiáng)度試驗(yàn)數(shù)據(jù)。Lesson13One of the primary considerations in designing any machine or structure is that the strength must be sufficiently greater that the stress to assure both safety and reliability. To assure that mechanical parts do not fail in service, it is necessary to learn why they sometimes do fail. Then we shall be able to relate the stresses with the strengths to achieve safety.在設(shè)計(jì)任何機(jī)器或者結(jié)構(gòu)時(shí)，所考慮的主要事項(xiàng)之一是其強(qiáng)度應(yīng)該比它所承受的應(yīng)力要大得多，以確保安全與可靠性。在軸承內(nèi)圈上加工出一個(gè)圓弧或者倒角，用來(lái)提供容納軸肩處圓弧半徑的空間。The inner race is frequently located axially by abutting against a shoulder .Aradius at this point is essential for the avoidance of stress concentration and ball races rae providede with a radius or chamfer to allow space for this .內(nèi)圈通常是通過(guò)緊靠在軸肩上進(jìn)行軸向定位的。It is not surprising that ,owing to the high stresses involved,a predominant form of failure shouls be metal fatigue,and a good deal of work is currently in progress intended to improve the reliability of this type of bearing . 滾動(dòng)軸承由于在工作中會(huì)產(chǎn)生高的應(yīng)力，其主要失效形式是金屬疲勞，這一點(diǎn)并不奇怪，目前正在進(jìn)行大量的工作以求改進(jìn)這種軸承的可靠性。The deflection of less magnitude than that of the shafts or other ponents associated with the bearing .當(dāng)載荷較大時(shí)，軸承零件的變形，盡管它通常小于軸和其它與軸承一起工作的零部件的變形，將會(huì)變得重要起來(lái)。因此，在為一個(gè)特定的用途選擇緊固件時(shí)，應(yīng)該考慮到上述各種可能性。以汽車為例，它是由數(shù)千個(gè)零件連接在一起而成為一輛車。人們對(duì)于任何產(chǎn)品的滿意程度不僅取決于其組成部件，還取決于其連接方式。緊固件是將一個(gè)零件與另一個(gè)零件進(jìn)行連接的零件。這是由剛性或者彈性聯(lián)軸器來(lái)實(shí)現(xiàn)的。例如，軸上的鍵槽會(huì)引起應(yīng)力集中，由于鍵槽的存在會(huì)使軸的橫截面積減小，會(huì)進(jìn)一步減弱軸的強(qiáng)度。3 、Components such as gears and pulleys are mounted on shafts