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本科生畢業(yè)設(shè)計(jì) 論文 外 文 翻 譯 原 文 標(biāo) 題 An intelligent fixture design method based on smart modular fixture unit 譯 文 標(biāo) 題 基本的加工工序 切削 鏜削和銑削 作者所在系別 機(jī)電工程學(xué)院 作者所在專業(yè) 機(jī)械設(shè)計(jì)制造及自動(dòng)化 作者所在班級(jí) B13113 作 者 姓 名 牛從從 作 者 學(xué) 號(hào) 20134011305 指導(dǎo)教師姓名 丁紅軍 指導(dǎo)教師職稱 講師 完 成 時(shí) 間 2017 年 3 月 北華航天工業(yè)學(xué)院教務(wù)處制 1 譯文標(biāo)題 基本的加工工序 切削 鏜削和銑削 原文標(biāo)題 Basic Machining Operations Turning Boring and Milling 作 者 B W Nile 譯 名 本 沃 聶邇 國 籍 加拿大 原文出處 Modern Manufacturing Process Engineering 譯文 基本的加工工序 機(jī)床是從早期的埃及人的腳踏動(dòng)力車床和約翰 威爾金森的鏜床發(fā)展而來的 它們用于為工件和刀具兩者提供剛性支撐并且可以精確控制它們的相對(duì)位置和相 對(duì)速度 一般來說 在金屬切削中用一個(gè)磨尖的楔形工具以緊湊螺紋形的切屑形 式從有韌性工件表面上去除一條很窄的金屬 切屑是廢棄的產(chǎn)品 與其工件相比 它相當(dāng)短但是比未切削的部分厚度有相對(duì)的增加 機(jī)器表面的幾何形狀取決于刀 具的形狀以及加工過程中刀具的路徑 不同的加工工序生產(chǎn)出不同幾何形狀的部件 如果一個(gè)粗糙的柱形工件繞中 心軸旋轉(zhuǎn)而且刀具穿透工件表面并沿與旋轉(zhuǎn)中心平行的方向前進(jìn) 就會(huì)產(chǎn)生一個(gè) 旋轉(zhuǎn)面 這道工序叫車削 如果以類似的方式加工一根空心管的內(nèi)部 則這道工 序就叫鏜削 制造一個(gè)直徑均勻變化的錐形外表面叫做錐體車削 如果刀具尖端 以一條半徑可變的路徑前進(jìn) 就可以制造出象保齡球桿那種仿形表面 如果工件 足夠短而且支撐具有足夠的剛性 仿形表面可以通過用一個(gè)垂直于旋轉(zhuǎn)軸的仿形 刀具來制造 短的錐面或柱面也可以仿形切削 常常需要的是平坦的或平的表面 它們可以通過徑向車削或端面車削來完成 其中刀具尖端沿垂直于旋轉(zhuǎn)軸的方向運(yùn)動(dòng) 在其他情況下 更方便的是固定工件 不動(dòng) 以一系列直線方式往復(fù)運(yùn)動(dòng)刀具橫過工件 在每次切削行程前具有一定橫 向進(jìn)給量 這種龍門刨削和牛頭刨削是在刨床上進(jìn)行的 大一些的工件很容易保 持刀具固定不動(dòng) 而像龍門刨削那樣在其下面拉動(dòng)工件 再每次往復(fù)進(jìn)給刀具 仿形面可以通過使用仿形刀具來制造 也可以使用多刃刀具 鉆削使用兩刃刀具 深度可達(dá)鉆頭直徑的 5 10 倍 不管是鉆頭轉(zhuǎn)動(dòng)還是工件轉(zhuǎn)動(dòng) 切削刃與工件之間的相對(duì)運(yùn)動(dòng)都是一個(gè)重要因素 在銑削作業(yè)中 有許多切削刃的旋轉(zhuǎn)銑刀與工件相接合 這種工件相對(duì)銑刀運(yùn)動(dòng) 緩慢 根據(jù)銑刀的幾何形狀和進(jìn)給的方式 可以加工出平面和仿形面 可以使用 水平或垂直旋轉(zhuǎn)軸 工件可以沿三個(gè)坐標(biāo)方向中的任意一個(gè)進(jìn)給 基本的機(jī)床 機(jī)床用于以切屑的形式從韌性材料上去除金屬來加工特殊幾何形狀和精密尺 寸的部件 切屑是廢品 其變化形狀從像鋼這樣的韌性材料的長的連續(xù)帶狀屑到 2 鑄鐵形成的易于處理 徹底斷掉的切屑 從處理的觀點(diǎn)來講 不想要長的連續(xù)帶 狀屑 機(jī)床完成 5 種基本的金屬切削工藝 車削 刨削 鉆削 銑削和磨削 其 他所有金屬切削工藝都是這 5 種基本工藝的變形 例如 鏜削是內(nèi)部車削 鉸削 錐體車削和平底锪孔則修改鉆孔 與鉆削有關(guān) 滾齒與切齒是基本銑削作業(yè) 弓 鋸削和拉削是銑削和磨削的一種形式 而研磨 超精加工 拋光和磨光是磨削和 研磨切削作業(yè)的各種變化形式 因此 僅有 4 種使用專用可控幾何形狀的刀具基 本機(jī)床 1 車床 2 刨床 3 鉆床 4 銑床 磨削工藝形成碎屑 但是磨粒 的幾何形狀不可控制 不同加工工藝切削的材料的數(shù)量和速度卻不相同 可能極大 如大型車削作 業(yè) 或者極小 如磨削和超精加工作業(yè) 只有表面高出的點(diǎn)被去除 機(jī)床完成 3 種主要功能 1 剛性支撐工件或工件夾具以及切削刀具 2 提 供工件與切削刀具之間的相對(duì)運(yùn)動(dòng) 3 提供了一定范圍的速度進(jìn)給 通常每種 有 4 32 種選擇 切削速度和進(jìn)給 切削速度 進(jìn)給量和切削深度是切削加工的 3 個(gè)主要變量 其他變量還有工 件和工具材料 冷卻劑以及切削刀具的幾何形狀 金屬切削的速率和加工所需的 功率就決定于這些變量 切削深度 進(jìn)給量和切削速度是任何金屬切削作業(yè)中必須都建立的變量 它 們都影響切削力 功率和對(duì)金屬切削的速率 可以通過把它們與留聲機(jī)的唱針和 唱片相比較給出定義 切削速度 V 由任意時(shí)刻唱片表面相對(duì)于拾音器支臂內(nèi) 部的唱針的速度來表示 進(jìn)給量由唱針每圈徑向向內(nèi)的前進(jìn)量或者由兩個(gè)相鄰槽 的位置差來表示 切削深度是唱針進(jìn)入的量或者是槽的深度 切削 那些在外表面上用單刃刀具完成的工序叫車削 除鉆削 鉸削和錐體車削外 在內(nèi)表面的作業(yè)也由單刃刀具完成 包括車削和鏜削在內(nèi)的所有加工工序都可以分為粗加工 精加工和半精加工 粗加工工序的目的是盡可能迅速且高效地去除大量的材料 在工件上只留下少量 的材料給精加工工序 精加工工序用以獲得工件最終的大小 形狀和表面粗糙度 有時(shí) 在精加工工序前進(jìn)行半精加工作業(yè)以便在工件上留下少的 預(yù)定的和均勻 量的原材料供精加工去除 通常 較長的工件是在一個(gè)或兩個(gè)車床頂尖的支撐下進(jìn)行的 用于安裝車床 頂尖的錐形孔叫做頂尖孔 它是在工件的端部鉆出的 通常沿著柱形部件的軸 心 與尾架鄰近的工件端部總是由尾架頂尖支撐 而挨著主軸箱的一端則由主軸 箱頂尖支撐或裝在卡盤內(nèi) 工件的主軸箱一端可以裝在一個(gè)四爪卡盤或套爪卡盤 3 內(nèi) 這種方法牢固地夾持工件并且把功率平穩(wěn)地傳送到工件上 由卡盤提供的額 外支撐減少了車削作業(yè)時(shí)發(fā)生震動(dòng)的傾向 如果仔細(xì)地將工件精確的固定在卡盤 上 用這種方法將獲得精密的結(jié)果 通過將工件支撐在兩個(gè)頂尖之間可以獲得非常精確的結(jié)果 一個(gè)車床夾頭夾 在工件上 然后由安裝在主軸前端的撥盤一起帶動(dòng) 先加工工件的一端 然后可 以在車床上將工件掉頭加工另一端 工件上的頂尖孔是用作精確定位面以及承受 工件重量和抵抗車削力的支撐面 在工件被拆下后 頂尖孔可以精確地將其裝回 機(jī)床 工件千萬不要同時(shí)通過卡盤和頂尖安裝在主軸箱一端 雖然這樣似乎是一 種快捷方法 但是這樣做使得工件受力不均勻 頂尖的對(duì)正作用不能維持 而且 爪的壓力可能損壞頂尖孔 車床頂尖甚至車床主軸 幾乎被獨(dú)自用在大量生產(chǎn)工 件上的補(bǔ)償或浮動(dòng)爪式卡盤是上述的一個(gè)例外 這些卡盤是自動(dòng)偏心夾緊卡盤不 能起到普通三爪或四爪卡盤同樣的作用 直徑非常大的工件雖然有時(shí)安裝在兩個(gè)頂尖上 但是最好用花盤把它們固定 在主軸箱端以獲得流暢的動(dòng)力傳輸 此外 可以把它們制造成專用部件 但是一 般不能提供足夠大的車床夾頭來傳輸動(dòng)力 除非是安裝在花盤上 其主軸軸承上 的外伸要比大卡盤上的少一些 鏜削 在車床上鏜孔的目的是 1 擴(kuò)孔 2 把孔加工到所需直徑 3 精確的為孔定位 4 在孔內(nèi)獲得好的表面粗糙度 當(dāng)?shù)毒邚较蛄锇蹇v向移動(dòng)而工件繞車床的軸線旋轉(zhuǎn)時(shí) 鏜刀的運(yùn)動(dòng)平行于車 床上的軸線 當(dāng)兩種運(yùn)動(dòng)結(jié)合起來鏜孔時(shí) 就會(huì)與車床的旋轉(zhuǎn)軸同心 通過把工 件固定在車床上可以精確定位孔的位置以使待加工孔所環(huán)繞的軸與車床的旋轉(zhuǎn)軸 一致 當(dāng)鏜削工序與用于車削和刮削工序的設(shè)置相同時(shí) 實(shí)際上可以達(dá)到理想的 同心與垂直 鏜刀固定在一根通過刀具徑向溜板進(jìn)給的鏜桿上 根據(jù)待做的工作來使用這 一設(shè)計(jì)的變化形式 如果有的話 所用的倒角總是應(yīng)該小些 而且 鏜刀前端的 半徑一定不能太大 用于鏜孔的切削速度可以等于車削速度 但是 在計(jì)算車床 主軸速度時(shí) 應(yīng)當(dāng)使用完成后的或最大的孔徑 鏜削的進(jìn)刀速度通常比車削的小 一點(diǎn)以補(bǔ)償鏜桿剛性的不足 鏜削工序一般分兩步完成 即粗鏜和精鏜 粗鏜工序的目的是快速 高效地 去除多余的金屬 而精鏜工序的目的是獲得所需的尺寸 表面粗糙度和孔的位置 4 孔的尺寸通過試切來獲得 孔的直徑可以用內(nèi)卡尺和千分尺測量 測量儀表或內(nèi) 千分卡尺直接測量直徑 型心孔和要鉆的孔有時(shí)相對(duì)于車床的旋轉(zhuǎn)是偏心的 當(dāng)鏜刀進(jìn)入工件時(shí) 鏜 桿在孔的一邊切口比另一邊深 當(dāng)采用這深切口時(shí)就會(huì)更偏斜 結(jié)果鏜的孔與工 件旋轉(zhuǎn)不同心 這一影響通過利用淺切口在整個(gè)孔加工中進(jìn)行幾次加工來糾正 因?yàn)槊總€(gè)淺切口形成的孔比使用深切口形成的孔更加同心 在完工前 進(jìn)行精加 工 孔應(yīng)該與工件的旋轉(zhuǎn)同心以確保完工時(shí)孔能精確定位 肩 溝槽 輪廓 錐度和螺紋也應(yīng)該在孔內(nèi)鏜出 內(nèi)槽是用與外部開槽工具 相似的工具切削 鏜削內(nèi)槽的步驟非常類似于車削肩部的步驟 大的肩部使用前 導(dǎo)裝置定位的鏜刀進(jìn)行刮削 使用橫向滑板進(jìn)給工具 內(nèi)部輪廓使用車床上的描 摹附件加工 仿行板附件安裝在橫向滑板上 靠模指跟隨標(biāo)準(zhǔn)剖面板的輪廓線運(yùn) 動(dòng) 這使刀具對(duì)應(yīng)于標(biāo)準(zhǔn)剖面樣板的輪廓線的路徑進(jìn)行移動(dòng) 這樣標(biāo)準(zhǔn)剖面樣板 的輪廓就在孔內(nèi)得到復(fù)制 標(biāo)準(zhǔn)剖面樣板精確安裝在一個(gè)專用的滑板上 滑板可 以在兩個(gè)方向上進(jìn)行精確調(diào)整以使刀具與工件以正確的關(guān)系對(duì)正 這臺(tái)車床有一 個(gè)偏心夾型的主軸前端 允許在任意一方向旋轉(zhuǎn)時(shí)進(jìn)行切削 正常的車削是在主 軸逆時(shí)針轉(zhuǎn)動(dòng)時(shí)進(jìn)行的 鏜削切削是在主軸順時(shí)針方向或 向后 轉(zhuǎn)動(dòng)時(shí)進(jìn)行的 這允許在孔的 后側(cè) 進(jìn)行鏜削切削 在車床前面 從操作者的位置易于看到后 孔 在具有螺紋主軸前端的車床上不應(yīng)這么做 因?yàn)榍邢髁Φ淖饔脮?huì)旋松卡盤 銑削 銑削是一種通過工件與多刃旋轉(zhuǎn)銑刀間的相對(duì)運(yùn)動(dòng)去除材料的加工工藝 在 一些應(yīng)用中 工件固定而旋轉(zhuǎn)的銑刀以一定進(jìn)給速度移過工件 橫向進(jìn)給 在 其他應(yīng)用中 工件與銑刀既彼此相對(duì)運(yùn)動(dòng) 又相對(duì)銑床運(yùn)動(dòng) 但是 更常見的是 工件以一個(gè)相對(duì)較低的運(yùn)動(dòng)速度或進(jìn)給速度朝正在高速旋轉(zhuǎn)的銑刀前進(jìn) 而銑刀 軸保持在一個(gè)固定位置 銑削工藝特有的性能是每個(gè)銑刀齒都以小的單個(gè)切屑的 形式切去一部分原料 可以在許多不同的機(jī)器上進(jìn)行銑削作業(yè) 由于工件和銑刀都可以彼此相對(duì)運(yùn)動(dòng) 銑削可以獨(dú)立的或以組合方式完成各 式各樣的作業(yè) 各種應(yīng)用包括平面或仿行面 窄槽 槽 退刀槽 螺紋和其他外 形的加工 銑削是一種最為通用而又復(fù)雜的加工方法 該工藝比任何其他基本加工方法 在所用機(jī)器的種類 工件運(yùn)動(dòng)以及加工工具種類方面都具有更多的變化 利用銑 削去除材料的重要優(yōu)點(diǎn)包括原料切削速度高 能形成相對(duì)光滑的表面粗糙度以及 可應(yīng)用的刀具更為多樣 刀具的切削刀刃可以仿行以形成任何復(fù)雜的表面 主要的銑削方法有周銑和端銑 此外 還有許多相關(guān)方法 他們屬于這 2 種 方法的變化形式 這些變化形式取決于工件或刀具的類型 5 周銑 在周銑 有時(shí)也叫平面銑削 中 由位于銑刀主體外周上的尺或刀片銑削的 面一般在一個(gè)與銑刀軸平行的平面上 使用鏟齒銑刀和成形銑刀完成的銑削工序 包括在這一類 銑削面的界面與所使用的銑刀或刀具組合的輪廓線或輪廓相符 周銑作業(yè)通常在帶有水平定位主軸的銑床上進(jìn)行 但也可以在帶有端面銑刀 的主軸銑床上進(jìn)行 銑刀安裝在心軸上 尤其是由于設(shè)置的條件 銑刀或者若干 銑刀位于距主軸前端一定距離處時(shí) 心軸一般在外端得到支撐來提高剛性 如果 部件可以端銑 一般不應(yīng)進(jìn)行周銑 端銑 端銑在臥式銑床和立式銑床上進(jìn)行 由位于銑刀外周和端面的切削刃聯(lián)合銑 削所形成的銑削面一般與銑刀軸成直角 除了在肩部銑削時(shí)外 銑削面是平的 與齒的輪廓形狀無關(guān) 一般來講 無論何時(shí)何地 只要可能就應(yīng)使用端銑 傳統(tǒng) 上 端銑中切屑厚度是變化的 在銑刀齒進(jìn)入和退出處最薄 而在沿 水平直徑處最大 銑削面由齒和專屬轉(zhuǎn)速痕跡表現(xiàn)其特征 這與周銑銑刀情況相 同 這些痕跡的起伏度由齒的端面切削刃的磨削精度或由刀體 刀片在可以指標(biāo) 化的刀具內(nèi)組合精度以及刀具安裝精度來控制 以使刀具在主軸上精確運(yùn)動(dòng) 起 伏度還由機(jī)器及工件本身的剛性來控制 當(dāng)端面切削刃的長度短于每轉(zhuǎn)的進(jìn)給量 或銑刀每轉(zhuǎn)一圈工件的移動(dòng)量 時(shí) 在銑面上就會(huì)形成一系列的環(huán)形凹槽或環(huán) 紋 當(dāng)后齒在工件的銑面上拖動(dòng)時(shí) 也會(huì)產(chǎn)生類似的標(biāo)記 這叫齒根拖動(dòng) 在端銑中 如果想獲得最佳結(jié)果 重要的是選擇銑刀具有適于所建議的切削 寬度的直徑 如果可能 應(yīng)避免切削寬度等與銑刀外徑相同 因?yàn)樵邶X的入口處 薄的銑屑界面會(huì)由于研磨加上銑屑有焊或粘到齒或刀片上并被帶來帶去或再次切 削的趨向而導(dǎo)致齒的加速磨損 這對(duì)表面粗糙度是有害的 好的銑刀直徑與工件 或提議的切削路線寬度之比是 5 3 6 原文 Basic Machining Operations Machining tools have evolved from the early foot powered lathe Egyptians and John Wilkinson s boring mill They are designed to provide rigid support for both the workpiece and the cutting tool and cutting tool and can precisely control their relative positions and the velocity of the tool with respect to the workpiece Basically in metal cutting a sharpened wedge shaped tool removes a rather narrow strip of metal from the surface of a ductile workpiece in the from of a severely deformed chip The chip is waste product that is workpiece in the from of a severely deformed chip is a waste product that is considerably shorter than the workpiece from which it came but with a corresponding increase in thickness of the uncut chip The geometrical shape of the machine surface depends on the shape of the tool and its path during the machining opration Most machine operations produce parts of differing geometry If a rough cylindrical workpiece revolves about a central axis and tool penetrates beneath its surface and travels parallel to the center of rotation a surface of revolution is produced and the operation is called turning If a hollow tube is on the machined on the inside in a similar manner the operation is called boring Producing an external conical surface of uniformly varying diameter is called taper turning If the tool point travels in a path of varying radius a contoured surface like that of bowling pin can be produced or if the piece is short enough and the support is sufficiently rigid a contoured surface could be produced by feeding a shaped tool normal to the axis of rotation Short tapered or cylindrical surfaces could also be contour formed Flat or plane surface are frequently required They can be generated by radial turning or facing in which the tool point moves normal to the axis of rotation In other cases it is more convenient to hole the workpiece steady and reciprocate the tool across it is series of straight line cuts with a crosswise feed increment before each cutting stroke This operation is called planning and is carried out on a shaper For larger pieces it is easier to keep the tool stationary and draw the workpiece under it as in planning The tool is fed at each reciprocation Contoured surfaces can be produced by using shaped tools Multiple edged tools can also be used Drilling uses a twin edged fluted tool for holes with depths up to 5 to 10 times the drill diameter Whether the drill turns or the workpiece rotates relative motion between the cutting edge and the workpiece is the important factor In milling operations a rotary cutter with a number of cutting edges 7 engages the workpiece which moves slowly with respect to the cutter Plane or contoured surfaces may be produced depending on the geometry of the cutter and the type of feed Horizontal or vertical axes of rotation may be used and the feed of the work piece may be in any of the three coordinate directions Basic Machine Tools Machine tools are used to part of a specified geometetrical shape and precise size by removing metal from a ductile material in the form chips The latter are a waste product and vary from long continuous ribbons of a disposal point of view to easily handed well broken chips resulting from cast iron Machine tools perform five basic metal remove processes turning planning drilling milling and grinding All other metal removal processes are modifications of these five basic processes For example boring is internal turning reaming tapping and counter boring mollify drilled holes and are related to drilling hobbling and gear cutting are fundamentally milling operations hack sawing and broaching are a from of planning and honing lapping super finishing polishing and buffing are variants of grinding or abrasive removal operations Therefore there are only four types of basic machine tools which use cutting tools of specific controllable geometry The grinding process forms chips but the geometry of the abrasive grain is uncontrollable The amount and rate of material removed by the various machining processes may be large as in heavy turning operations or extremely small as in lapping or superfinishing operations where only the high spots of a surface are removed A machining tool performs three major functions 1 it rigidly supports the workpice or its holder and the cutting tool 2 it provides relative motion between the workpice and the cutting tool 3 it provides a range of feeds and speeds usually ranging from 4 to32 choices in each case Speed and Feeds in Machining Speeds feeds and depth pf cut are the three major variables for economical machining Other variables are the work and tool materials coolant and geometry of the cutting tool The rate of metal removal and power required for machining depend upon these variables The depths of cut feed and cutting speed are machine setting that must be established in any metal cutting operation They all affect the forces the power and the rate of metal removal They can be defined by comparing them to the needle and record of a phonograph The cutting speed V is represented by the velocity of the record 8 surface relative to the needle in the tone arm at any instant Feed is represented by the advance of the needle radially inward per revolution or is the difference in position between two adjacent grooves The depth of cut is the penetration of the needle into the record or the depth of the grooves Turning on lathe centers The basic operations operations performed on an engine lathe are illustrated in fig 11 3 those operations performed on external surfaces with a single point cutting tool are called turning Except for drilling reaming and tapping the operations on internal surfaces are also performed by a single point cutting tool All machining operate including turning and boring can be classified as roughing finishing or semi finishing The objective of a roughing operation is to remove the bulk of the material as rapidly and as efficiently as possible while leaving a small amount of material on the work piece for the finishing operation Finishing operations are performed to obtain the final size shape and surface finish on the workpiece Sometimes a semi finishing operation will precede the finishing operation to leave a small predetermined and uniform amount of stock on the work piece to be removed by the finishing operation Generally longer workpieces are turned while supported on one or two lathe centers Cone shaped holes called center holes which fit the lathe centers are drilled in the end of the workpiece usually along the axis of the cylindrical part The end of the workpiece adjacent to the tailstock is always supported by a tailstock center while end near the headstock may be supported by a headstock center or held in a chuck The headstock end of the workpiece may be held in a four jaw chuck or in a collet type chuck This method holds the workpiece firmly and transfers the power to the workpiece smoothly the additional support to the workpiece provided by the chuck lessens the tendency for chatter to occur when cutting Precise result can be obtained with this method if care is taken to hold the workpiece accurately in the chuck Very precise results can be obtained by supporting the workpiece between two centers A lathe dog is clamped to the workpiece together they are driven by the driver plate mounted on the spindle nose One end of the workpiece is machined then the workpiece can be turned around in the lathe to machine to other end The center holes in the workpiece serve as precise locating surfaces as well as bearing surfaces to carry the weight of the workpiece and to resist the cutting forces After the workpiece has been remove from the lathe for any reason the center holes will accurately align the 9 workpiece back in the lathe or in another lathe or in a cylindrical grinding machine The workpiece must never be held at the headstock end by both a chuck and a lathe center While at first thought this seems like a quick method of aligning the workpiece in the chuck this must not be done because it is not possible to press evenly with the jaws against the workpiece while it is also supported by the center The alignment provided by the center will not be maintained and the pressure of the jaws may damage the center hole the lathe center and perhaps even the lathe spindle Compensating or floating jaw chucks used almost exclusively on high production work provide an exception to the statements made above These chucks are really work drivers and cannot be used for the same purpose as ordinary three or four jaw chicks While very large diameter workpiece are sometimes mounted on two centers they are preferably held at the headstock end by faceplate jaws to obtain the smooth power transmission moreover large lathe dogs that are adequate to transmit the power not generally available although they can be made as a special Faceplate jaws are like chuck jaws except that they are mounted on a faceplate which has less overhang from the spindle bearings than a large chuck would have Boring The objective of boring a hole in a lathe is 1 To enlarge the hole 2 To machine the hole to the desired diameter 3 To accurately locate the position of the hole 4 To obtain a smooth surface finish in the hole The motion of the boring tool is parallel to the axis of the lathe when the carriage is moved in the longitudinal direction and the work piece revolves about the axis of the lathe When these two motions are combined to bore a hole it will be concentric with the axis of rotation of the lathe The position of the hole can be accurately located by holding the work piece in the lathe so that the axis about which the hole is to be machined coincides with the axis of rotation of the lathe When the boring operation is done in the same setup of the work that is used to turn and face it practically perfect concentricity and perpendicularity can be achieved The boring tool is held in a boring bar which is fed through the hole by carriage Variations of this design are used depending on the job to be done The lead angle used if any should always be small Also the nose radius of the boring tool must not be too large The cutting speed used for boring can be equal to the speed for turning However 10 when the spindle speed of the lathe is calculated the finished or largest bore diameter should be used The feed rate for boring is usually somewhat less than for turning to compensate for the rigidity of the boring bar The boring operation is generally performed in two steps namely rough boring and finish boring The objective of the rough boring operation is to remove the excess metal rapidly and efficiently and the objective of the finish boring operation is to obtain the desired size surface finish and location of the hole The size of the hole is obtained by using the trial cut procedure The diameter of the hole can be measured with inside calipers and outside micrometer calipers Basic Measuring Instrument or inside micrometer calipers can be used to measure the diameter directly Cored holes and drilled holes are sometimes eccentric with respect to the rotation of the lathe When the boring tool enters the work the boring bar will take a deeper cut on one side of the hole than on the other and will deflect more when taking this deeper cut with the result that the bored hole will not be concentric with the rotation of the work This effect is corrected by taking several cuts through the hole using a shallow depth of cut Each succeeding shallow cut causes the resulting hole to be more concentric than it was with the previous cut Before the finale finish cut is taken the hole should be concentric with the rotation of the work in order to make certain that the finished hole will be accurately located Shoulders grooves contours tapers and threads are also bored inside of holes Internal grooves are cut using a tool that is similar to external grooving tool The procedure for boring internal shoulder is very similar to the procedure for turning shoulders Larger shoulders are faced with the boring tool positioned with the nose leading and using the cross slide to feed the tool Internal contours can be machined using a tracing attachment on a lathe The tracing attachment is mounted on the cross slide and the stylus follows the outline of the master profile plate This causes the cutting tool to move in a path corresponding to the profile of the profile plate Thus the profile on the master profile plate is reproduced inside the bore The master profile plate is accurately mounted on a special slide which can be precisely in two directions in order to align the cutting tool in the correct relationship to the work This lathe has cam lock type of spindle nose which permits it to take a cut when rotating in either direction Normal turning cuts are taken with the spindle rotating counterclockwise The boring cut is taken with the spindle revolving in a clockwise direction or backwards This permit the boring cut to be taken on the back side of the bore which is easier to see 11 from the operator s position front of the lathe This should not be done on lathes having a threaded spindle nose because the cutting force will tend to unscrew the chuck Milling Milling is a machining process for removing material by relative motion between a workpiece and a rotating cutter having multiple cutting edges In some applications the workpiece is held stationary while the rotating cutter is moved past it and a given feed rate traversed In other applications both the workpiece and cutter are moved in relation to each other and in relation to the milling machine More frequently however the workpiece is advanced at a relatively low rate of movement or feed to a milling cutter rotating at a comparatively high speed with the cuter axis remaining in a fixed position a characteristic feature of the milling process is that each milling cutter tooth takes its share of the stock in the form of small individual chips Milling operations are performed on many different machines Since both the workpiece and cutter can be moved relative to one another independently or in combination a wide variety of operations can be performed by milling Applications include the production of flat or contoured surfaces slots grooves recesses threads and other configurations Milling is one of the most universal yet complicated machining methods The process has more variations in the kinds of machines used workpiece movements and types of tooling than any other basic machining method Important advantages of removing material by means of milling include high stock removal rates the capability of producing relatively smooth surface finishes and the wide variety if cutting tools that are available Cutting edges of the tools can be shaped to form any c