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河南理工大學(xué)萬方科技學(xué)院 本科畢業(yè)設(shè)計（論文）開題報告 題目名稱 滾筒式絞車傳動系統(tǒng)設(shè)計 學(xué)生姓名 王群星 專業(yè)班級 08機設(shè)2班 學(xué)號 0828070028 一、 選題的目的和意義： 隨著國民經(jīng)濟對燃料和各種礦物需要量的不斷增長，礦井生產(chǎn)機械化、自動化和集中化程度的不斷提高，各種礦物的產(chǎn)量亦不斷擴大；我國煤礦和各類礦山每年都要生產(chǎn)大量的煤和礦石。為了使礦井生產(chǎn)能夠正常地進行和充分發(fā)揮設(shè)備的效能，目前在礦井井下主要運輸環(huán)節(jié)之間普遍設(shè)置了各類的煤倉，以調(diào)節(jié)和緩和各運輸環(huán)節(jié)的能力，使之連成一個有機的整體，以保證煤和礦石源源不斷地運到地面上來。因此，提升絞車礦井生產(chǎn)中的一個十分重要的環(huán)節(jié)，而煤倉的設(shè)計也成為礦井設(shè)計中重要的內(nèi)容。 礦井提升絞車是礦山重要和關(guān)鍵的設(shè)備之一，是礦山生產(chǎn)的“咽喉"設(shè)備，主要用于煤礦、 金屬礦及非金屬礦提升和下放人員、 提升煤炭、 礦石、 矸石及運輸材料和設(shè)備。提升絞車主要裝置由卷筒、傳動系統(tǒng)等組成。它的性能優(yōu)劣，運行是否正常，工作效率是否高，是否安全可靠，對礦山生產(chǎn)和人員、設(shè)備的安全有著重要的影響，為了適應(yīng)我國國民經(jīng)濟的高速發(fā)展，煤炭冶金工業(yè)要求建立大量的現(xiàn)代化礦山，提升機的市場前景樂觀；同時，由于國內(nèi)提升絞車生產(chǎn)廠家多，競爭激烈，對傳統(tǒng)提升機的設(shè)計方法提出挑戰(zhàn)，市場的競爭要求設(shè)計者推陳出新，瞄準國際提升機的發(fā)展方向，設(shè)計出質(zhì)量過硬性能最優(yōu)的產(chǎn)品，以滿足礦山行業(yè)要求。所以，對其進行現(xiàn)代設(shè)計研究，對于強化提升機的生產(chǎn)，提高效益具有重要意義。相信隨著課題的不斷深入，對帶式輸送機將會有更深入的了解，為以后的學(xué)習(xí)也能打下夯實的基礎(chǔ)。 此設(shè)計其意義重大。通過這一過程，我們達到以下目的： 1、鞏固、擴大和深化我們以前所學(xué)的基礎(chǔ)課、專業(yè)課知識； 2、培養(yǎng)我們綜合分析、理論聯(lián)系實際的能力； 3、培養(yǎng)我們調(diào)查研究，正確熟練運用國家標準、手冊、圖冊等資料、工具的能力； 4、鍛煉自己的設(shè)計計算、數(shù)據(jù)處理、編寫技術(shù)資料、繪圖等獨立工作能力； 5、培養(yǎng)團隊精神、合作意識的能力。 二、 國內(nèi)外研究綜述： （1）國外礦井提升絞車的研究概述 國外礦用絞車使用很普遍，生產(chǎn)廠家也很多。蘇聯(lián)、美國、日本、瑞典等國都制造了礦用小絞車，而且，國外礦用絞車種類、規(guī)格較多，比如調(diào)度絞車牽引力100kgfd到3600kdf,動力有電動的，液力的，風(fēng)動的。事實證明，生產(chǎn)需求是推動技術(shù)發(fā)展的最大動力，現(xiàn)在國外的提升機一次提升量最大已達50噸，提升速度接近20米／秒，最大拖動功率達10000千瓦，井深百米到2000米以上。隨著科學(xué)技術(shù)的發(fā)展，直流拖動正在廣泛使用，計算機的應(yīng)用也在逐漸推廣，所有這些，都說明礦井提升設(shè)備正在日新月異，向大型化，高效率和自動控制方向發(fā)展。近年來，隨著世界銷售市場對礦山機械需求量的不斷增加，國外各種提升機制造企業(yè)在生產(chǎn)中不斷的采用優(yōu)化設(shè)計、機械自動化和自動化設(shè)備以提高勞動生產(chǎn)率。機械產(chǎn)品的現(xiàn)代化設(shè)計方法研究及應(yīng)用在美國、日本、德國等國均有較高的技術(shù)水平和經(jīng)濟效益，就提升機領(lǐng)域而言，采用CAD技術(shù)，可節(jié)約成本20％左右，而且其使用壽命可長達15年左右。國外提升機發(fā)展到今天，已經(jīng)到了比較成熟的地步，其結(jié)構(gòu)形式基本上都是經(jīng)過反復(fù)優(yōu)化設(shè)計，并經(jīng)過實踐檢驗的。隨著計算機技術(shù)的廣泛應(yīng)用，許多國外提升機制造商應(yīng)用計算機輔助設(shè)計系統(tǒng)（CAD）以及模塊化設(shè)計方法，盡量使用標準件設(shè)備迅速組合和安裝，減少標準件外組合部分的加工制造。組合構(gòu)件的使用對生產(chǎn)非標準件提升機來講，有助于減少成本。 （2）國內(nèi)礦井提升絞車研究概述 我國絞車只是經(jīng)歷了仿制、自行設(shè)計兩個階段。解放初期使用的產(chǎn)品主要來自日 本與蘇聯(lián)，1958年以后，這些產(chǎn)品相繼被淘汰，并對蘇聯(lián)絞車進行了改進，與1964年進入自行設(shè)計階段?；茨厦簷C廠曾設(shè)計了擺線齒輪絞車和少齒差動絞車，徐州礦山設(shè)備制造廠也曾設(shè)計制造了擺線和行星齒輪和傳動絞車，一些廠家還設(shè)計試制了25kw的調(diào)度絞車。目前，礦用小絞車已經(jīng)在標準化方面得到了相應(yīng)的發(fā)展，與1952年對以前制定的標準進行了修訂。其標準分為JB965-83,JB1409-93。 三、 畢業(yè)設(shè)計（論文）所用的主要技術(shù)與方法： 1、在學(xué)校圖書館查閱相關(guān)資料； 2、通過老師和工程師的指導(dǎo)； 3、通過瀏覽網(wǎng)上相關(guān)資料； 4、通過對相關(guān)資料和數(shù)據(jù)的理論計算和分析; 5、利用計算機PRE和CAD繪制相關(guān)圖。 四、 主要參考文獻與資料獲得情況： 《機械工程手冊》 第二版 （傳動設(shè)計卷） ——機械工業(yè)出版社 《實用機械設(shè)計手冊》 吳相憲 王正為 黃玉堂 主編 ——中國礦業(yè)大學(xué)出版社 《機械設(shè)計》 濮良貴 紀名剛 主編 ——高等教育出版社 《機械原理》 孫恒 陳作模 主編 ——西北工業(yè)大學(xué)機械原理及機械零件教研室 編 《理論力學(xué)》 ——哈爾濱工業(yè)大學(xué)理論力學(xué)教研室 編 《材料力學(xué)》 劉鴻文 主編 ——高等教育出版社 《礦山機械》 李炳文 主編 ——中國礦業(yè)大學(xué)出版社 《電動滾筒設(shè)計與選用手冊》 劉建勛 主編 ——化學(xué)工業(yè)出版社 《摩擦制動器——原理、結(jié)構(gòu)與設(shè)計》 王濤 朱文堅 主編 ——華南理工大學(xué)出版社 五、 畢業(yè)設(shè)計（論文）進度安排（按周說明） 1、第一到二周進行畢業(yè)設(shè)計選題。 2、第三到四周布置和明確設(shè)計任務(wù)，查閱收集相關(guān)設(shè)計資料。 3、第五到六周完成開題報告，報告指導(dǎo)老師審批。 4、第七到十一周確定滾筒式絞車傳動方案并對課題進行設(shè)計計算。 5、第十二到十四繪制有關(guān)圖，并書寫畢業(yè)設(shè)計說明書。 6、第十五周報告指導(dǎo)老師進行檢查。 7、第十六周熟悉答辯流程，進行畢業(yè)答辯。 指導(dǎo)教師審批意見： 指導(dǎo)教師： （簽名） 年 月 日 河南理工大學(xué)萬方科技學(xué)院 本科畢業(yè)設(shè)計（論文）中期檢查表 指導(dǎo)教師： 王 德 勝 職稱： 教 授 所在院（系）： 機械與動力工程學(xué)院 教研室（研究室）： 機 設(shè) 題 目 滾 筒 式 絞 車 傳 動 系 統(tǒng) 設(shè) 計 學(xué)生姓名 王群星 專業(yè)班級 08機設(shè)2班 學(xué)號 0828070028 一、 選題質(zhì)量： 1、本題目符合機械設(shè)計專業(yè)的培養(yǎng)目標，能夠充分鍛煉和培養(yǎng)分析問題和實際操作能力，能夠體現(xiàn)綜合訓(xùn)練的要求。 2、設(shè)計任務(wù)難易程度和工作量適中，符合本科畢業(yè)設(shè)計要求，能在規(guī)定的時間內(nèi)完成。 3、所選題目礦井提升設(shè)備的傳動系統(tǒng)設(shè)計與實際貼合比較緊密，在實際的應(yīng)用中比較廣泛。在設(shè)計過程中，對機器的零件的設(shè)計和計算對我來說是以往所學(xué)知識的總結(jié)和應(yīng)用，所以能夠滿足綜合訓(xùn)練的要求。滾筒式絞車傳動系統(tǒng)在設(shè)計過程中，對于我來說還是具有很大的難度，對于這方面的了解不是很多，且這方面的資料也是比較少，所以這對我來說是一個挑戰(zhàn)。 二、開題報告完成情況： 根據(jù)自己在各方面資料的收集和整理，通過對可行性的分析，結(jié)合老師給的題目的選擇，我完成了這次設(shè)計的選題。在選題結(jié)束之后，結(jié)合老師給的數(shù)據(jù)綜合分析并通過自己認真查閱相關(guān)的資料，最后結(jié)合本身的實際情況和設(shè)計的時間任務(wù)完成了開題報告。 三、階段性成果： 現(xiàn)階段主要成果有以下幾點： 完成畢業(yè)實習(xí)并完成實習(xí)報告； 完成開題報告； 完成各傳動部件的詳細計算； 已收集整理各種資料并準備繪制圖樣。 四、存在主要問題： 現(xiàn)階段存在的主要問題有：一是資料的查找比較困難，關(guān)于滾筒式絞車的資料非常復(fù)雜和 繁瑣，其中許多都是與設(shè)計無關(guān)的，需要耗費大量的時間尋找；二是結(jié)合傳動系統(tǒng)的結(jié)構(gòu)確 定整體尺寸比較困難；三是其中牽扯到許多專業(yè)知識，許多地方都是在課堂上沒有接觸過的， 還有一些牽扯到實際中的情況，一些設(shè)計細節(jié)也是以前在課本上沒見過的，需要自己努力分析確 定其結(jié)構(gòu)。 解決方法：1 靜心認真查找并整理相關(guān)資料 2 查找相關(guān)書籍資料學(xué)習(xí)專業(yè)知識 3 請教老師和專業(yè)相關(guān)同學(xué) 4 上網(wǎng)尋求幫助 五、指導(dǎo)教師對學(xué)生在畢業(yè)實習(xí)中，勞動、學(xué)習(xí)紀律及畢業(yè)設(shè)計（論文）進展等方面的評語 指導(dǎo)教師： （簽名） 年 月 日 英文材料 Lathe and Turning The Lathe and Its Construction A lathe is a machine tool used primarily for producing surfaces of revolution flat edges. Based on their purpose ,construction , number of tools that can simultaneously be mounted , and degree of automation ,lathes or, more accurately, lathe-type machine tools can be classified as follows: (1) Engine lathes (2) Toolroom lathes (3) Turret lathes (4) Vertical turning and boring mills (5) Automatic lathes (6) Special-purpose lathes In spite of that diversity of lathe-type machine tools, they all have all have common features with respect to construction and principle of operation .These features can best be illustrated by considering the commonly used representative type, the engine lathe. Following is a description of each of the main elements of an engine lathe , which is shown in Fig.11.1. Lathe bed . The lathe bed is the main frame , involving a horizontal beam on two vertical supporis. It is usually made of grey or nodular cast iron to damp vibrations and is made by casting . It has guideways to allow the carriage to slide easily lengthwise. The height of the lathe bed should be appropriate to enable the technician to do his or her jib easily and comfortably. Headstock. The headstock is fixed at the left hand side of the lathe bed and includes the spindle whose axis is parallel to the guideways (the silde surface of the bed) . The spindle is driven through the gearbox , which is housed within the headstock. The function of the gearbox is to provide a number of different spindle speeds (usually 6 up to 18 speeds) . Some modern lathes have headstocks with infinitely variable spindle speeds, which employ frictional , electrical , or hydraulic drives. The spindle is always hollow , I .e ,it has a through hole extending lengthwise. Bar stocks can be fed througth that hole if continous production is adopted . A lso , that hole has a tapered surface to allow mounting a plain lathe center . The outer surface of the spindle is threaded to allow mounting of a chuck , a face plate , or the like . Tallstock . The tailstock assembly consists basically of three parts , its lower base, an intermediate part, and the quill . The lower base is a casting that can slide on the lathe bed along the guidewayes , and it has a clamping device to enable locking the entire tailstock at any desired location , depending upon the length of the workpiece . The intermediate parte is a casting that can be moved transversely to enable alignment of the axis of the the tailstock with that of the headstock . The third part, the quill, is a hardened steel tube, which can be moved longitudinally in and out of the intermediate part as required . This is achieved through the use of a handwheel and a screw , around which a nut fixed to the quill is can be locked at any point along its travel path by means of a clamping device. The carriage. The main function of the carriage is mounting of the cutting tools and generating longitudinal and /or cross feeds. It is actually an H-shaped block that slides on the lathe bed between the headstock and tailstock while being guided by the V-shaped guideways of the bed . The carriage can be moved either manually or mechanically by means of the apron and either the feed rod or the lead screw. When cutting screw threads, power is provided to the gearbox of the apron by the lead screw. In all other turning operations, it is the feed rod that drives the carriage. The lead screw goes through a pair o half nuts , which are fixed to the rear of the apron . When actuating a certain lever, the half nuts are clamped together and engage with the rotating lead screw as a single nut, which is fed , together with carriage, along the bed . when the lever is disengaged , the half nuts are released and the carriage stops. On the other hand , when the feed rod is used, it supplies power to the apron through a wrom gear . The latter is keyed to feed rod and travels with the apron along the feed rod , which has a keyway extending to cover its whole length. A modern lathe usually has a quick-change gearbox located under the headstock and driven from the spindle through a train of gears. It is connected to both the feed rod and the lead screw and enables selecting a variety of feeds easily and rapidly by simply shifting the appropriate levers, the quick-change gearbox is employed in plain turning, facing and thread cutting operations. Since that gearbox is linked to spindle, the distance that the apron (and the cutting tool) travels for each revolution of the spindle can be controlled and is referred to as the feed. Lathe Cutting Tools The shape and geometry of the lathe tools depend upon the purpose for which they are employed. Turning tools can be classified into tow main groups,namely,external cutting tools and internal cutting tools , Each of these groups include the following types of tools: Turning tools. Turing tools can be either finishing or rough turning tools . Rough turning tools have small nose radii and are used for obtaining the final required dimensions with good surface finish by marking slight depth of cut . Rough turning tools can be right –hand or left-hand types, depending upon the direction of feed. They can have straight, bent, or offset shanks. Facing tools . Facing tools are employed in facing operations for machining plane side or end surfaces. There are tools for machining left-hand-side surfaces and tools for right-hand-side surfaces. Those side surfaces are generated through the use of the cross feed, contrary to turning operations, where the usual longitudinal feed is used. Cutoff tools. Cutoff tools ,which are sometimes called parting tools, serve to separate the workpiece into parts and/or machine external annual grooves. Thread-cutting tools. Thread-cutting tools have either triangular, square, or tranpezoidal cutting edges, depending upon the cross section of the desired thread .Also , the plane angles of these tools must always be identical to those of the thread forms. Thread-cutting tools have straight shanks for external thread cutting and are of the bent-shank type when cutting internal threads . Form tools. Form tools have edges especially manufactured to take a certain form, which is opposite to the desired shape of the machined workpiece . An HSS tools is usually made in the form of a single piece ,contrary to cemented carbides or ceramic , which are made in the form of tipes. The latter are brazed or mechanically fastened to steel shanks. Fig.11.2 indicates an arrangement of this latter type, which includes the carbide tip , the chip breaker ,the pad ,the clamping screw (with a washer and a nut ) , and the shank.. As the name suggests, the function of the chip breaker is to break long chips every now and then , thus preventing the formation of very long twisted ribbons that may cause problems during the machining operations . The carbide tips ( or ceramic tips ) can have different shapes, depending upon the machining operations for which they are to be employed . The tips can either be solid or with a central through hole ,depending on whether brazing or mechanical clamping is employed for mounting the tip on the shank. Lathe Operations In the following section , we discuss the various machining operations that can be performed on a conventional engine lathe. It must be borne in mind , however , that modern computerized numerically controlled lathes have more capabiblities and do other operations ,such as contouring , for example . Following are conventional lathe operations. Cylindrical turning . Cylindrical turning is the the simplest and the most common of all lathe operations . A single full turn of the workpiece generate a circle whose center falls on the lathe axis; this motion is then reproduced numerous times as a result of the axial feed motion of the tool. The resulting machining marks are , therefore ,a helix having a very small pitch, which is equal to the feed . Consequently , the machined surface is always cylindrical. The axial feed is provided by the carriage or the compound rest , either manually or automatically, whereas the depths of cuts is controlled by the cross slide . In roughing cuts , it is recommended that large depths of cuts (up to 0.25 in. or 6 mm, depending upon the workpiece material) and smaller feeds would be used. On the other hand , very fine feeds, smaller depth of cut (less than 0.05in. , or 0.4 mm) , and high cutting speeds are preferred for finishing cuts. Facing . The result of a facing operation is a flat surface that is either the whole end surface of the workpiece or an annular intermediate surface like a shoulder . During a facing operation ,feed is provided by the cross slide, whereas the depth of cut is controlled by the carriage or compound rest . Facing can be carried out either from the periphery in ward or from the center of the workpiece outward . It is obvious that the machining marks in both cases tack the form of a spiral. Usually, it is preferred to clamp the carriage during a facing operation, since the cutting force tends to push the tool ( and , of course , the whole carriage ) away from the workpiece . In most facing operations , the workpiece is held in a chuck or on a face plate. Groove cutting. In cut-off and groove-cutting operations ,only cross feed of the tool is employed. The cut-off and grooving tools , which were previously discussed, are employed. Boring and internal turning . Boring and internal are performed on the internal surfaces by a boring bar or suitable internal workpiece is solid, a drilling operation must be performed first . The drilling tool is held in the tailstock, and latter is then fed against the workpiece. Taper turning . Taper turning is achieved by driving the tool in a direction that is not paralled to the lathe axis but inclined to it with an angle that is equal to the desired angle of the taper . Following are the different methods used in taper-turning practice: Rotating the disc of the compound rest with an angle to half the apex angle of the cone . Feed is manually provided by cranking the handle of the compound rest . This method is recommended for taper turning of external and internal surfaces when the taper angle is relatively large. Employing special form tools for external , very short ,conical surfaces . The width of the workpiece must be slightly smaller than that of the tool ,and the workpiece is usually held in a chuck or clamped on a face plate . I n this case , only the cross feed is used during the machining process and the carriage is clamped to the machine bed . Offsetting the tailstock center . This method is employed for esternal tamper turning of long workpiece that are required to have small tamper angles (less than 8 ) . The workpiece is mounted between the two centers ; then the tailstock center is shifted a distance S in the direction normal to the lathe axis. Using the taper-turning attachment . This method is used for turning very long workpoece , when the length is larger than the whole stroke of the compound rest . The procedure followed in such cases involves complete disengagement of the cross slide from the carriage , which is then guided by the taper-turning attachment . During this process, the automatic axial feed can be used as usual . This method is recommend for very long workpiece with a small cone angle , i.e. , 8 through 10 . Thread cutting . When performing thread cutting , the axial feed must be kept at a constant rate , which is dependent upon the rotational speed (rpm) of the workpiece . The relationship between both is determined primarily by the desired pitch of the thread to be cut . As previously mentioned , the axial feed is automatically generated when cutting a thread by means of the lead screw , which drives the carriage . When the lead screw rotates a single revolution, the carriage travels a distance equal to the pitch of the lead screw rotates a single revolutional speed of the lead screw is equal to that of the spindle ( i. e . , that of the workpiece ), the pitch of the resulting cut thread is exactly to that of the lead screw . The pitch of the resulting thread being cut therefore always depends upon the ratio of the rotational speeds of the lead scew and the spindle : Pitch of the lead screw rpm of the workpiece = spindle-to-carriage gearing ratio Desired pitch of workpiece rpm of lead screw This equation is usefully in determining the kinematic linkage between the lathe spindle and the lead screw and enables proper selection of the gear train between them . n thread cutting operations , the workpiece can either be held in the chuck or mounted between the two lathe centers for relatively long workpiece . The form of the tool used must exactly coincide with the profile the thread to be cut , I . e . , triangular tools must be used for triangular threads , and so on . Knurling . knurling is mainly a forming operation in which no chips are prodyced . Tt involves pressing two hardened rolls with rough filelike surfaces against the rotating workpiece to cause plastic deformation of the workpiece metal. Knurling is carried out to produce rough , cylindrical ( or concile )surfaces , which are usually used as handles . Sometimes , surfaces are knurled just for the sake of decoration ; there are different types of patterns of knurls from which to choose . Cutting Speeds and Feeds The cutting speed , which is usually given in surface feet per minute (SFM), is the number of feet traveled in circumferential direction by a given point on the surface (being cut ) of the workpiece in one minute . The relationship between the surface speed and rpm can be given by the following equation : SMF =3.14*DN Where D= the diameter of the workpiece in feet N=the rpm The surface cutting speed is dependent primarily upon the machined as well as the material of the cutting and can be obtained from handbooks , information provided by cutting tool manufacturera , and the like . generally , the SFM is taken as 100 when machining cold-rolled or mild steel ,as 50 when machining tougher metals , and as 200 when machining sofer materials . For aluminum ,the SFMis usually taken as 400 or above . There are also other variables that affect the optimal value of the surface cutting speed . These include the tool geometry, the type of lubricant or coolant , the feed , and the depth of cut . As soon as the cutting sped is decided upon , the rotational speed (rpm) of the spindle can be obtained as follows : SFM =3.14*D The selection of a suitable feed depends upon many factors , such as the required surface finish , the depth of cut , and the geometry of the tool used . Finer feeds produce better surface finish ,whereas higher feeds reduce the machining time during which the tool is in direct contact with the workpiece . Therefore ,it is generally recommended to use high feeds for roughing operations and finer feeds for finishing operations. Again, recommend values for feeds , which can be taken as guidelines , are found in handbooks and information booklets provided by cutting tool manufacturers. Here I want to introduce the drilling and milling : Drilling involves producing through or blind holes in a workpiece by forcing a tool , which rotates around its axis , against the workpiece .Consequently , the range of cutting from that axis of rotation is equal to the radius of the required hole .In practice , two symmetrical cutting edges that rotate about the same axis are employed . Drilling operations can be carried out by using either hand drills or drilling machines . The latter differ in size and construction . nevertheless , the tool always rotates around its axis while the workpiece is kept firmly fixed . this is contrary to drilling on a lathe . Cutting Tool for Drilling Operations In drilling operations , a cylindrical rotary-end cutting , called a drill , is employed . The drill can have either one or more cutting edges and corresponding flutes , which can be straight or helical . the function of the flutes is to provide outlet passages for the chips generated during the drilling operation and to allow lubricants and coolants to reach the cutting edges and the surface being machined . Following is a survey of the commonly used drills. Twist drill . The twist drill is the most common type of drill .It has two cutting edges and two helical flutes that continue over the length of the drill body , as shown in Fig 12.1 The drill also consist of a neck and a shake that can be either straight or tapered .In the latter case , the shank is fitted by the wedge action into the tapered socket of the spindle and has a tang , which goes into a slot in the spindle socket ,thus acting as a solid means for transmitting rotation . On the other hand , straight –shank drills are held in a drill chuck that is , in turn , fitted into the spindle socket in the same way as tapered shank drills. As can be seen in FIG.12.1 , the two cutting edges are referred to as the lips , and are connected together by a wedge , which is a chisel-like edge . The twist drill also has two margins , which enable proper guidance and locating of the drill while it is in operation . The tool point angle (TPA) is formed by the lips and is chosen based on the properties of the material to be cut . The usual TAP for commercial drills is 118 , which is appropriate for drilling low-carbon steels and cast irons . For harder and tougher metals , such as hardened steel , brasss and bronze , larger TPAs (130 OR 140 ) give better performance . The helix angle of the flutes of the commonly used twist drills ranges between 24 and 30 . When drilling copper or soft plastics , higher values for the helix angle are recommended (between 35 and 45). Twist drills are usually made of high speed steel ,although carbide tipped drills are also available . The size of twist drills used in industrial range from 0.01 up to 3.25 in . (i.e.0.25 up to 80 mm ) . Core drills . A core drill consists of the chamfer , body , neck ,and shank , as shown in Fig 12.2 . This type of drill may be have either three or four flutes and an equal number of margins , which ensure superior guidance , thus resulting in high machining accuracy . It can also be seen in Fig 12.2 that a core drill has flat end . The chamfer can have three or four cutting edges or lips , and the lip angle may vary between 90 and 120 . Core drills are employed for enlarging previously made holes and not for originating holes . This type of drill is characterized by greater productivity , high machining accuracy , and superior quality of the drilled surfaces . Gun drills . Gun drills are used for drilling deep holes . All gun drills are straight fluted , and each has a single cutting edge . A hole in the body acts as a conduit to transmit coolant under considerable pressure to the tip of the drill . There are two kinds of gun drills , namely , the center cut gun drill used for drilling blind holes and the trepanning drill . The latter has a cylindrical groove at its center , thus generating a solid core , which guides the tool as it proceeds during the drilling operation. Spade drills . Spade drills are used for drilling large holes of 3.5 in .(90 mm ) or more . Their design results in a marked saving in cost of the tool as well as a tangible reduction in its weight , which facilitates its handling . moreover , this type of drill is easy to be ground . Milling and Milling Cutters Milling is a machining process that is carried out by means of a multiedge rotating tool known as a milling cutter . In this process ,metal removal is achieved through combining the rotary motion of the milling cutter and linear motions of the workpiece simultaneously . Milling operations are employed in producing flat ,