【正文】 gear can be gripped axially between a shoulder on the shaft and a spacer ,with torque being transmitted through a keyways.Lesson7Fasteners are devices which permit one part to be joined to a second part and ,hence,they are involved in almost all designs . The acceptability of any product depends not only on the selected ponents , but also on the means by which they are fastened together. The principal purposes of fasteners are to provide the following design features。因此，幾乎在所有的設(shè)計(jì)中都要用到緊固件。The importance of fasteners can be realized when referring ro any plex product,In the case of the automobile,there are literally thousands of parts which are fastened together to produce the total failure or loosening of a single fastener could result in a simple nuisance such as a door rattle or in a serious situation such as a wheel ing off.Such possibilities must be taken into account in the selection of the type of fatener for the specific application.通過任何一個(gè)復(fù)雜的產(chǎn)品，都可以認(rèn)識(shí)到緊固件在其中的重要性。一個(gè)緊固件的失效或松脫可能會(huì)帶來像車門嘎嘎響這類小麻煩，也可能造成像車輪脫落這種嚴(yán)重的后果。Lesson8Threaded fasterners perform the function of locating ,clamgping ,adjusting ,and transmiting force from one machine member to another .They are thoroughly standardized and generally designed for use in mass production of machines. Matching external and internal threads so that they are may be assembled is the key to all thread fasteners. A particular SAE grade specilication can be met by a number of different steels, thus faster manufacturers have some latitude in selecting the materials best suited to their specific production faclities. For moderate loads and speedes the correct selection of a standard of the bearing on the basis of load rating will usually secure satisfactory performance. 對(duì)于中等載荷和轉(zhuǎn)速，根據(jù)額定負(fù)荷選擇一個(gè)標(biāo)準(zhǔn)軸承，通常都可以保證其具有令人滿意的工作性能。Lesson9Where speeds are high special cooling arrangements bee necessary which may increase frictional drag .在轉(zhuǎn)速高的場(chǎng)合需要有專門的冷卻裝置，而這可能會(huì)增大摩擦阻力。 The fit of the bearing races onto the shaft or onto the housing is of critical importance because of their bined effect on the internal clearance of the bearing as well as preserving the desired degree of interference fit.軸承套圈與軸或軸承座的的配合非常重要，因?yàn)樗鼈冎g的配合不僅應(yīng)該保證所需要的過盈量，而且也應(yīng)該保證軸承的內(nèi)部間隙。軸肩出的圓弧半徑主要是為了避免應(yīng)力集中。Where life is not the determing factor in design ,it is usual to determine maximum loading by the amount to which a bearing will deflect under load .在使用壽命不是設(shè)計(jì)中的決定因素的場(chǎng)合，通常根據(jù)軸承受載荷時(shí)產(chǎn)生的變形量來確定其最大載荷。要保證機(jī)械零件在使用過程中不發(fā)生失效，就必須知道它們?cè)谀承r(shí)候會(huì)失效的原因，然后，才能將應(yīng)力與強(qiáng)度聯(lián)系起來，以確保其安全。這些試驗(yàn)應(yīng)該在與所設(shè)計(jì)的零件有相同的熱處理，表面粗糙度和尺寸大小的試件進(jìn)行，而且試驗(yàn)應(yīng)該在與零件使用過程中承受的載荷完全相同的情況下進(jìn)行。因此，硬度可以表示為所產(chǎn)生的壓痕尺寸函數(shù)。通?？梢灾苯釉趯?shí)際的機(jī)械零件上進(jìn)行硬度試驗(yàn)。 (b) functional。設(shè)計(jì)通?？梢苑譃閹讉€(gè)明確的階段；（a）概念設(shè)計(jì)；b 功能設(shè)計(jì) c 生產(chǎn)設(shè)計(jì)。Often a prototype or working model is made that can be tested to permit evaluation of the product as to function, reliability, appearance, serviceability, and so on. 通常要制造出樣機(jī)或著實(shí)物模型，并對(duì)其進(jìn)行實(shí)驗(yàn)，評(píng)價(jià)產(chǎn)品的功能、可靠性、外觀和維修保養(yǎng)性等As manufacturing progresses, it is inevitable that situations will arise that may require modifications of the materials being used. Experience may reveal that substitution of cheaper materials can be made. 在制造過程中，不可避免地會(huì)出現(xiàn)對(duì)使用中的材料做一些更改的情況。24/27課Working drawings are the drawings from which a design is implemented. All principles of orthographic projection and techniques of graphics can be used to municate the details of a project in working drawings. A detail drawing is a working drawing of a single part (or detail) within the set of working drawings. 工作圖是將設(shè)計(jì)變?yōu)閷?shí)際產(chǎn)品所依據(jù)的圖樣。零件圖是在一整套工作圖中關(guān)于一個(gè)零件（或細(xì)節(jié)）的工作圖。另外，還可以包含公差、審核人員和材料等信息。The allocation of proper production tolerances is therefore a most important task if the finished product is to achieve its intended purpose and yet be economical to produce. The size of the tolerances, as specified