车削中心结构（运动）分析及加工工艺的研究与应用设计含CAD图
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附录一：车床中心床身这是车床的基础,铸铁制造,它通常是一个非常健壮盒子那样的形式,内部冷却剂和切屑可以轻松通过。顶部表面的床上,被称为“方法”准确地加工和经常硬,满意的工作在很大程度上依赖于车床的对齐表面通常由精密磨削完成。 差距的床许多车床是由短差距在床上在主轴承,这前面增加了车床的能力将大车轮和滑轮。小型机器中,差距通常留下永久开放,但在较大的机器提供了负担最大支持运输加工正常工作时接近主轴承。主轴承在左边,在形式的一根粗精确定位和主轴承栓在床上。这是偶尔一块车床床。主轴承的承载在精密轴承主轴必须采取和径向加载结束。他们通常的圆锥滚子类型和组装,预装消除轴向游动和侧隙主轴。主轴是中空的,适应和内孔加工标准锥度接受生活中心或其他配件的要求。的标准莫尔斯锥度是车床上使用英语。生活的中心是所谓的,因为它是一个总是旋转工作和与驱动有关。空心轴促进生活中心的弹射杆穿过孔的长度。传统的英语主轴的是螺纹,轻叩,可以在对一个肩膀和一个普通螺纹部分(注册),对齐组件。主轴承内部的驱动机制和基本训练车床,这常常是一个简单的四到五步锥轮主轴,由一个相同的滑轮安装相反的方向轮在轴由电机驱动。这个范围内四个或五个速度加倍的螺丝车床通过齿轮机构这样可以减少一组比速度。背齿轮用于螺钉切割和低它给是有用的在把大直径和速度加工硬质材料。贝尔驱动的移动了滑轮没有必要完全做好主轴承,皮带传动装配带来力量, 之后,速度变化通过齿轮,从外部手动操作控制。结合一英尺主轴刹车操作,全齿轮头使速度变化的非常快的操作,但是刹车只能安装在轻叩(等等)直接安装在主轴。看下查克配件”速度变化的另一种方法避免停止改变皮带在使用两个不同宽度的 v 字形的滑轮。分裂的底部 v 字形和作为一个滑轮打开沿着轴,另一个关闭,三角带沉没在一个滑轮,因为它打开时,同时上升关闭其他滑轮。这给无限变速范围可调整与机器运行。尾座尾座支持“免费”的工作,也用于钻铰孔工作在卡盘或面板上举行。幻灯片, 由床身导轨,在大多数车床由两部分组成,允许横向调整。这是用于歪。铸造是无聊来接收筒(或“套”)的轴是精确与主轴。内桶加工结束接收锥形中心可固定或旋转。桶用于控股。锥柄钻头、铰刀或其他配件。外一端,筒螺纹是由手轮一起的调节螺丝。 主要调整尾座的位置是由滑动沿着床和它通过操作杆夹紧它,之后,精细调整,使中心的工作可以用手轮。桶也可以夹紧后设置,以便它不能工作期间偷懒。运输或鞍这种形式的基础单位,支持刀具和它可以遍历整个床的长度由手控或电力饲料。它可以夹在任何时候在床上。十字滑提供交叉穿越或“浮出水面”,在这个幻灯片安装复合幻灯片(顶部滑动),可以旋转,锁在任何角度使用把短的蜡烛。前面的马车是固定的围裙远远播种的前面床上,这里有发现控制手-或权力 喂养浮出水面时,滑动或螺纹。马车的齿条和齿轮,手轮将小齿轮和齿条安装的手。螺杆传送的螺杆螺旋切削进给运动,扩展了整个长度床上,通过后面的围裙。它可以从事,或者从马车由离合器释放机制可同时操作螺杆正在转向。这个离合器非常简单,组成的一个大型分离螺母(半坚果),可以打开或关闭对螺杆围裙上的杆的运动。这种机制只是螺纹时使用。轴除了螺杆,一个提要轴用于操作马车或十字架下滑自动转向。螺杆不用于此目的,避免穿它不需要为它工作(这是一个昂贵的项目),也因为提要给会常常是太快了。提要轴槽(纵槽),与螺杆和运行通过后面的围裙的蜗轮,安装在轴上,并自由滑动。蜗轮驱动齿轮,从这个提要导演十字架幻灯片或者马车通过操作控制的围裙。在一些车床、丝杠本身是由一个键槽的线程。键槽驱动器蜗轮和螺钉用于螺纹。自动将是非常有用的在长遍历,马车的稳定运动给上级完成,通常通过手喂养。没有一分是在结束面对自动进料是不可能保持一个恒定速度以来的切割速度在外围的工作将是其最大,这将减少向中心。在这些情况下必须寻求妥协。螺杆的运动和提要轴来自主轴,因为革命的丝杠螺纹的轴,必须积极相关开车总是通过一个齿轮火车。这个问题处理下更充分“螺纹”,就目前而言,这将是足以知道的传动比主轴螺杆可以改变削减各种螺纹球,旋转螺杆和饲料轴可以被逆转,或者两者都可以开车的时候不是必需的。大多数车床安装了某种安全装置,防止意外同时参与多个饲料,或在两个提要在一起,防止危害,有时或滑动离合器机制在任何异常载荷剪切销的优惠。车床大小车床的大小通常表示在英国的高度在车床中心床上,指示圆柱体的半径将清晰的床上,但通常的“摇摆”车床是引用,这指的是这样一个气缸的直径。无论大小表示,我们必须记住,转弯时必须明确车床马车之间的中心。车床的床长度并不表明其引用的能力中心之间的长度。控股和驾驶每一个车床应配备两个轻叩,一个查克和另一个 4-jaw 卡盘,车床制造商推荐的大小。两种类型用于许多不同的加工操作短片段可以工作查克举行,而不再项目可以支持在尾座中心或稳定外。当然,长杆的长度,可以通过空心轴同时正确传递查克的抱怨。抛掷 3-jaw SC 查克将自动中心轮或六边形打开或关闭滚动转化的关键。大白鲨是匹配滚动在制造和每个编号,这样就可以返回正确的槽后删除。对大直径的工作,滚动抛掷提供备用的下巴相反的步骤。大白鲨本身不能逆转。把下巴,查克打开,直到所有三个下巴可以撤回他们脱离卷轴。重新装配用的下巴在以下方式:对于开放和滚动当螺杆一端从 1 号槽已经消失了,第一下巴按家里订婚通过关闭卡盘。当滚动结束出现在第二槽,它将返回一个小和 2 号下巴按家里与滚动。这是重复 3 号下巴。抛掷也由两个,四个和六个下巴,和这些,只有 4-jaw 卡盘可能会发现在学校车间使用,因为它将棒料中心广场。下巴与外部措施可以用来举行大型环或管通过打开的内部的工作。滚动放弃将中心与合理的精度,但除非非常小心,很快就会被赶出真理,主要由穿或滚动的紧张过度紧缩的下颚和滚动在这把沉重的负荷,特别是如果从查克短工件被扭曲。查克下巴应在定期删除清洗间隔的滚动,下颌牙齿和幻灯片。不是一个好事,因为过剩的石油将被否决或将形成一个破坏性的磨削与任何细木屑复合。不准确定心的作用可以通过规划查克无效,这样所有的工作重要操作进行设置的工作。一旦删除工作很难使其运行真正的再次。独立的下巴轻叩而持有的 4-jaw 卡盘是必不可少的工作的形状不规则和不平衡的,它也可以用于持有广场或轮。集中一段时间但它可以非常准确地使用每一个个体下巴调整。卡盘定心的过程是描述在卡盘。独立的下巴轻叩只提供一套下巴因为这些是可逆的。拉紧弹簧夹头。拉紧夹头提供了一个快速而准确的方法小零件模型、仪器和时钟。热处理钢,夹头套的形式,无聊,六角和方钢密切近似孔的大小。夹头,分成三个或更多的部分,是卷入与螺纹车床主轴管(拉杆),对匹配的锥度锥形接头熊在一个适配器或“近”车床主轴和筒夹关闭工作。因为它的限制范围调整,有必要将每个尺寸和一个夹头部分的酒吧加工,这可能意味着很多。这种大范围的调整,需要更少的有缝夹套,总共二十持有任何规模的酒吧1.5 毫米和 62 毫米之间,一轮六角。这些有缝夹套的一部分集成系统的工作持有任何一个夹头可用于关闭设备包括:(1) 主要经营轻叩车床工作;(2) 杆或权力运作抛掷,可以打开或关闭机器运行。也有垂直安装夹头用于铣床和钻床或工具持有者用于绞盘和自动车床。在亦可卡盘钥匙旋转收紧套在其轴承座圈。线程在的这枚戒指吸引回关闭环这是禁止的该指南的关键。这个闭合环夹头回了锥形住房、关闭叶片。配件多年来,安装在轴头卡盘的正常方法已经通过线程和主轴,注册后松的螺丝。卡盘,在它把螺栓后,板。在首次大会,后松螺丝轴头,然后面对和完成死大小放入凹槽形成的查克。然后两人拧在一起,从那时起,查克和背面板,“属于”特定的车床。注意力被吸引到 plain-shouldered 部分注册),中心卡盘。这个安装展览一些不受欢迎的特性越来越趋势抛掷直接安装在主轴不同国际标准规范。这些轴头形式提供的优势是:(1) 注册很积极和不受磨损时发生轻叩螺纹在轴;(2) 查克是持有非常安全,没有危险的“流失”当车床停止(即使轴装有刹车); (3)减少过剩和查克更接近轴承整体更严格的组合,使更好的工作;(4)查克快速安装和删除,除了与卡盘的类型在半永久的安装法兰螺栓。任何形式的使用越来越多,这是非常重要的主轴和卡盘在装配前寄存器和线程是很干净的。当删除抛掷,操作员应该准备采取的重量会突然到来,以避免损坏车床床或者你的手指。软木块,放在车床床好事故预防越来越趋势抛掷直接安装在主轴不同国际标准规范。这些轴头形式提供的优势是:面板这个配件是用于安装工作不能容易的尴尬的形状丢掉。收集盘收集盘,安装在车床主轴通常用于驱动之间的工作中心、驱动销与“载体”(或 “狗”),螺丝的结束工作。通常用径向槽的脸,这样驾驶销移除,bent-tail 航母可以用于驱动尾槽。车床中心这些通常由高速钢和硬化,但事实上,它不是必不可少的生活中心(主轴)硬化是没有摩擦。尾座中心也由硬质合金小费给长期和艰巨的服务。中心通常精确地标准的蜡烛点完一个夹角吗 60 度。生活中心适应主轴套筒通过锥套。至关重要的是,中心能装在主轴和尾座桶和之前插入他们应擦拭干净,检查损伤,最轻微的去毛刺蜡烛的使他们的真理。主轴和尾座蜡烛还需要关注和清洁应该完成了破布上一根棍子(不是手指), 从不与主轴旋转。尾座中心几乎被收回时桶和家里,螺丝将排出的结束中心。尾座中心需要润滑,因为正在和它的工作调整到工作必须认真,这样所有轴向游动是没有任何消除过度的压力将热量和扩大在重切削,将在中心和绑定如果不是缓解压力的损害再度调整。长酒吧几乎可以肯定显示足够的扩张导致绑定只有温度和略有上升中心的调整和润滑必须认真观看。尾座生活中心生活(旋转)尾座中心的使用消除了摩擦(但不是工作扩张)。其他类型是由服务和各种不同条件的形式,包括定心管的锥形适配器。精密轴承,旋转中心径向和推力加载和精致的预防措施来防止切屑的入口或冷却剂。人生的轴承润滑和单位不应该需要拆除。一半中心使用半中心促进工作的端面中心之间允许美联储在该工具。与正常的端面中心,工具提示地面在不到 60 度。的整形中心第一次穿的迹象,中心分必须和这可能完成一个刀架磨床(一个自包含磨床),安装在滑动设置在 30。主轴承的中心旋转缓慢,磨石是遍历,慢慢地,沿着锥来回,只有很轻的削减。当最好的完成与磨床已经实现,可以给定一个锥高完成通过磨练一个完全平坦的石头。床身和幻灯片在覆盖磨让所有喷丸。马车停止这是一个非常有用的装置停止马车沿着床在预先确定的点并可用于重复完成部分相同刻度盘十字架,上滑板手轮子都配有刻度表盘给准确滑动运动的迹象在设定的深度削减。拨号的形式领通常旋转手轮,通过摩擦传动,允许的吗独立的旋转。这使得一个设定的深度从零读数将削减刻度盘,在不改变工具的位置。读取拨毕业典礼与零线刻滑的身体。必须记住,任何调整的交叉幻灯片将翻倍工作直径除非车床配备了一个直读刻度盘显示了数量直径。由于市场需求,英国现在生产供应车床的操。(1)公制,即与度量距丝杠和刻度盘在毫米(读书 0.02 毫米), (2)英语术语,即与英语节导螺杆,拨打了阅读,至 0.001ns,(3) 的组合,例如英语距丝杠毫米表盘阅读或双重阅读刻度盘给英寸或度量阅读。这些刻度盘可以作为标准设备安装新机器或可以安装机器已经在使用。他们是专为单一的阅读,即当设置为读指标,只有寸毕业典礼可见,当设置为读指标, 只有度量毕业典礼是可见的。的转换,瞬时,带来的滑动或顶针,太阳和行星的系统吗轮子给精确转换从英寸到毫米工具的帖子美国环和摇臂的帖子显示手持工具但它可以用于工具持有人。工具正在迅速调整中心高度通过移动床上的摇臂宽松的环。四柱更适合重复工作周期的操作在哪里被执行,但无论如何,这将是偶尔在学校车间使用。现代刀架分配设置需要包装,这种调整是通过滚花螺钉。工具,仍然在其持有人,可以快速删除磨和替换时不需要调整。车床工具然而好的车床,其高效的操作和完成其产品的质量将依赖于使用的工具。除了工具的实际形状,材料它是至关重要的,本质的韧性使它能够抵御冲击和沉重的压力,和硬度使它举行尖端。尽管碳素工具钢适当热处理时,这些属性应用程序是有限的,它在很大程度上取代了高铁钢和其他合金保留更长时间的尖端,在严格得多条件,即:重削减在升高的温度下没有失去他们的硬度。空气硬化高速钢的属性可用于硬质材料。其他合金指的是有色,他们是极其困难和脆性(且昂贵),用于提示的形式焊接或对接焊接的小腿,通常的高强度钢。倾斜工也由消耗品技巧都与一个小夹,当举行到位沉闷的,提示被丢弃,取而代之的是一个新的。钨铬钴合金(的合金钴、铬和钨)是用于制造技巧和最难的是由硬质合金(例如,碳化钨)。所有允许的切削速度可能远远超过这些高速钢。车床工具可分为四组:(1) 固体碳(整体)工具或高速钢,直接笼罩在刀架(2)刀架的高速钢和广场或圆形截面。在工具持有人; (3)将各种工具;特殊的工具,如钻孔工具,无聊的酒吧持有工具位、迪比特,形成的工具各种和滚花的工具。工具的角度楔形式的车刀的切削部分包括两个部分,即,间隙低于前沿,没有工作只能擦的工具,和耙脸上的斜坡,远离前沿。而间隙略有不同不同的目的,耙显示显著的变化,根据金属被调整，方向主要取决于饲料方向和前沿的形状。间隙间隙,形成的主要和次要的侧翼工具保持尽可能小可能,符合适当的工作的工具。过度的间隙减少支持前沿和增加了喋喋不休的倾向。除了轻微的变化间隙对不同金属的,有很多情况下,需要进一步调整,即:(1) 由于凸的在转动,工作前切割工具将操作稍微减少间隙,但不削减浮出水面;(2) 遍历的削减,正确的间隙,因为可能需要略微增加螺旋形式的瞬态表面变得更加明显,除非进给速度减少;(3) 无聊的工具将需要增加凹工作间隙,避免摩擦表面。第二个侧面将提供救济在脚跟和很小的孔,这个次要的角可能会非常大。削减行动脆性硬黄铜和铸造等金属工具铁,很少或根本没有形成耙,dell 面对工作导致废金属在小芯片剪切和打破。在金属形式流动的芯片(和许多金属这样做)工具必须有耙,因为废金属不能强迫被剪切,但必须解除楔形行动的具。芯片的压力非常可观的,沉重的削减和工具切割部分削弱了过度耙或间隙将容易造成喋喋不休和挖掘“喂养”效应的压力在倾斜的脸上。耙将产生尽可能最小的芯片偏转而离开切削部分不够硬承受加载不出来。为非常困难金属耙很小,例如,大约 10 工具钢,增加到 30 或更多的柔软和韧性金属像铜和铝。“喂养”效应的压力在倾斜的脸上。耙将产生尽可能最小的芯片在图 2 - 5 的例子说明 rake 方向影响芯片的线流瞬态表面。同时这是一个很重要的功能设计的工具。也有其他因素需要考虑的因素。工具几何形状可能是分割的几何形状工具最复杂,尽管如图 2 - 6 所示与主要的尖端垂直于工具轴,通常形成于一个小角度给干净的突破。的工具如图 2 - 5 所示,进给运动的方向符合飞机的正常水平耙和工具集车床,有一个简单和明显的关系使工具之间的角度和表面。FIG.2-6 车床和工具命名法和角度工具,然而,生产各种方向的切削刃在使用中,工具柄可在任何角度与工作表面。这样的角度由工具切削刃、脸和相对于合成切削方向和侧翼工作表面被称为面向的工作角度这并不总是容易的以制作或工具的磨英国标准学会的建议在解决这些问题涉及两个系统的使用参考飞机通过选定点的前沿通过这些工具角度,可以定义工作角度。第一,被称为系统定义的几何工具来促进生产而另一系统,定义了几何时执行一个有效的工具切割操作。术语定义耙、间隙和其他刀具角度被称为“正常的 rake 系统”,它是首选的系统取代前者的最大倾角系切削速度切削速度通常表达的米每分钟的速度工具应该通过工作在合适的速度产生最好的结果。切削速度都是由两个因素:金属的硬度降低;(1) 所使用的类型,高速钢,速度远高于工具操作碳钢的工具。(2) 保持这样的速度,小直径的工作不得不将比更大的快得多直径。平稳两种稳定的用于支持长时间的工作压力的工具。的固定稳定安全的车床床身而稳定的安装在马车旅行和行动背后的工作工具,因为每个削减。固定的稳定的可以使用支持的酒吧,笼罩在卡盘,端面、中心钻、无聊或线程。打开中心中心钻中的第一个操作将工作中心之间的钻洞越来越多的工作,为此,结合钻和埋头(中心钻)。三个类型的钻(A,B 和 R),但只有双头类型被认为是在这里底部的孔穿孔树叶间隙的点和车床中心提供了一个水库,润滑剂。中心钻车床时,酒吧可以传递通过主轴如果不是太大,3-jaw 卡盘。适当的切削液应该使用和钻不能撞到或强迫,因为这可能会导致工作吗分裂和停止工作。如果酒吧大孔径太大,它可以笼罩在查克的自由端在一个固定的稳定的支持。当一个酒吧必须完成中心之间的长度,机械加工留量不应过度,否则轴承表面的中心也会变得轻微,当面对。将示例一件作品将在中心与建议图 2 - 7 所示所涉及的操作。酒吧应该切断了足够长的时间来允许运营商和一些车刀的间隙。FIG.2-7 把例子(1) 两端应面对和中心钻 3 或 4 个中心钻。最后面对,应该小心避免离开中心“皮普”可能导致中心钻开始中心。(2) 工件中心装有一个直接的载体。背面中心调整必须小心,以避免过度的压力和摩擦。许多车工填补这一中心孔最初脂和在任何情况下,必须润滑中心工作期间, 与石油。工作期间,懈怠的中心通常是表示从传动销声引人注目的承运人尾(或抓板槽)削减开始。背面中心应检查间隔取暖。(3) 如果工具面临的结束是左刀架,它可以使用,有固定工作,文士短线作为指南设置下一个工具准确中心高度。(4) 初学者使用弯曲的工具可能会感到更安全,因为他们将工作艘航母。(5) 减少大小的酒吧是开始用手穿过,当工作接近成品尺寸,罚款可以进行自动进料,用完很好地磨练工具。酒吧应该清楚地标明表明限制转向避免引人注目的承运人。应该使用切削油自由促进良好的完成。(6) 注意,定位套筒不穿过洞,这确保了螺母紧框架。(7) 扭转工作重复操作,开车可能会更方便龙头,使用一个较小的载体与完成铜垫, 以防损坏表面。长度可以在肩膀与滑动卡尺或规则检查测量认为是令人满意的, 在这种情况下,某种停止应向左侧举行肩膀上的测量。(8) 将因为这项工作是一个锻炼,车床,线程应该削减主题是在一个单独的加热处理。在调整尾座之前,它首先是夹轻轻后释放的一个调整螺丝,用于将尾座对这样的小工具在尾座锥形。螺丝是最后收紧。抵消一个粗略的测量是通过阅读发现基准线规模尾座基地,但可以抵消的事实, 从一块短的测量相当准确酒吧在刀架举行。酒吧和尾座桶之间的差距来衡量的游标卡尺在尾座抵消,形成这是扣除所需的测量偏移量。尾座可以超过这个距离。测量的补偿也可以设置工作完成中心和拨号计在刀架,抵消了一个已知的距离可以准确地在工作测量。当然,必须在中心高度刻度盘柱塞。非常重要的一点,绝不能被忽视在锥形车削是工具必须设置完全指向中心高度否则将生成错误的锥度。锥形车削对中心的影响,应该考虑是同时工作轴倾斜的车床轴,中心保持平行。这种不均匀的影响中心可能是在轻微的蜡烛的后果很小,但陡峭的蜡烛,这不是一个好的事情。使用活尾座中心在摩擦不均匀的问题,有限的程度。螺纹车床在螺纹车床马车是遍历已经触及了短暂,这是放大的图 2 - 8 显示了如何运动从轴丝杠和马车在“传统”车床。在主轴承,第一个司机开车从主轴,逆转机制, 是封闭的。减少一个线程的特定的球场,有必要精确的旋转相关的工作,这是通过改变车轮的大小齿轮火车。在所有情况下,螺杆的螺距必须考虑,因为这将影响旋转时的比率转化为横向运动。附录二：The Center Lathe The BedThis is the foundation of the lathe, and made in cast iron, it is usually ofa very robust box-like form, robbed on the inside and ported so that coolant and swarf can pass through easily.The top surfaces of the bed, known as the ways are accurately machined and often hardened,the satisfactory working of the lathe being very largely dependent on the alignment of thesesurfaces which are usually finished by precision grinding. Gap BedMany lathes are made with a short gap in the bed in front of the headstock and this increases the capacity of the lathe for turning large wheels and pulleys. In smaller machines, the gap is usually left permanently open but in larger machines, a gap-piece is provided to afford maximum support for the carriage when normal work is being machined close to the headstock.HeadstockAt the left, and in the form of a stout box-casting, the headstock is precisely located and bolted to the bed. It is occasionally cast in one piece with the lathe bed. The headstock carries the spindle in precision bearings which must take both radial and end loads. They are usually of the tapered-roller type and on assembly, are pre-loaded to eliminate end-float and side-play in the spindle.The spindle is hollow, to accommodate long bars in the chuck and the inner end of the bore is machined to a standard taper to receive the live center or other accessories as required. The Morse standard taper is used on English lathes. The live center is so called because it is the one which always rotates with the work and is associated with the driving. The hollow spindlefacilitates the ejection of the live center with a length of rod passed through the bore.The traditional English spindle nose is threaded so that chucks, face- and catch-plates can be screwed on against a shoulder and over a plain portion (register) which aligns the component.The driving mechanism is inside the headstock and in a basic training lathe for young pupils, this is often simply a four- or five-step cone pulley on the spindle, driven by an identical pulley mounted the opposite way round on a lay shaft which is driven by the motor. This range of four or five speeds is doubled in the screw cutting lathe by engaging a back gear mechanism which reduces all speeds in a set ratio. The back gear is used in screw cutting and the low speeds it gives are useful in turning large diameters and machining hard materials.The moving of the bell drive on stepped pulleys is not necessary in the all-geared headstock in which one belt drive brings power into the assembly, after which, speed changes are made through gears, operated from external hand controls. In conjunction with a foot operated spindle brake, the all-geared head makes speed changing a very fast operation, but brakes can only be fitted where chucks (etc.) are directly mounted on the spindle. See underChuck mountings.Another method of speed changing which avoids stopping to change a belt over employs two variable-width vee pulleys. Both split at the bottom of the vee and as one pulley opens out along the axis, the other closes, the vee belt sinking in one pulley as it opens, whilst rising in the other pulley as it closes. This gives an infinitely variable speed range which can be adjustedwith the machine running. TailstockThe tailstock supports the free end of the work and s used also in the drilling and reaming of work held in chuck or on face-plate. It slides on and guided by the bed-ways and in most lathes is made in two parts which permit of a lateral adjustment. This is used in off-center taper-turning. The casting is bored to receive the barrel (or sleeve) whose axis is precisely in linewith that of the spindle. The inner end of the barrel is machined to receive the tapered center which can be of the stationary or rotating kind. The taper-socket in the barrel is used for holding taper-shank drills, reamers or other accessories.At the outer end, the barrel is threaded to takethe adjusting screw which is operated by a hand-wheel.Major adjustments to the location of the tailstock are made by sliding it along the bed and clamping it by operating a lever, after which, fine adjustments to bring the center up to the work can be made with the hand-wheel. The barrel also, can be clamped after setting, so that it cannot slack off during working.Carriage or SaddleThis forms the base of the unit which supports the cutting tool and it can be traversed along the whole length of the bed by hand control or by power feed. It can be clamped at any point along the bed. A cross slide is provided for cross traversing or surfacing and on this slide is mounted the compound slide (top slide) which can be pivoted and locked at any angle for use inturning short tapers.To the front of the carriage is fixed the apron which extends well sown over the front of the bed and here are found the controls for hand- or power- feeding when surfacing, sliding or screw-cutting. Hand-traversing of the carriage is by rack and pinion, the handwheel turning thepinion and the rack being fitted under the over hand of the bed-way.Lead-screwThe lead-screw, which transmits feed motion for screw cutting, extends the whole length of the bed, passing behind the apron. It can be engaged with, or freed from the carriage by a clutch mechanism which can be operated whilst the lead-screw is turning. This clutch is quite simple,consisting of a large split nut (half nuts) which can be opened or closed over the lead-screw bythe movement of the lever on the apron. This mechanism is only used when screw-cutting.Feed ShaftIn addition to the lead-screw, a feed shaft is employed in operating the carriage or the cross slide in automatic turning. The lead-screw is not used for this purpose to avoid wearing it on work for which it is not needed (it is a costly item) and also because the feed it gives would often be too fast.The feed shaft, with a key-way (a lengthwise slot), runs alongside the lead-screw and passes behind the apron where a keyed worm wheel, mounted on the shaft, turns with it and is free to slide along it. The worm wheel drives a gear wheel and from this, the feed can be directed either to the cross slide or to the carriage by operating a control on the apron. On some lathes, the lead-screw itself is made with a keyway cut through the threads. The keyway drivesthe worm wheel and the screw is used for screw-cutting.Automatic turning is very useful in long traverses, the steady movement of the carriage giving a superior finish to that usually obtained by hand feeding. One point to not is that in end facing with automatic feed it is impossible to maintain a constant cutting speed since the speedat the work periphery will be at its maximum and this will diminish towards the center. A Technical English Through Reading compromise must be sought in these situations.The motion for the lead-screw and the feed shaft is taken from the spindle and because the revolutions of the lead-screw must be positively related to the spindle for screw-cutting, the drive is always taken through a gear train. This subject is dealt with more fully under Screw-cutting and for the moment, it will be sufficient to know that the velocity ratio of spindle to lead-screw can be changed to cut various thread pitches, that the rotation oflead-screw and feed shaft can be reversed and that either or both can be taken out of drive when not required.Most lathes are fitted with some kind of safety device which either prevents the accidental engagement of more than one feed at the same time, or in the event of two feeds being engaged together, prevents damage being done, sometimes with a slipping clutch mechanism or with a shear pin which breaks under any abnormal load. Lathe SizesThe size of a lathe is commonly expressed in the UK by the height of the centers over the lathe bed, indicating the radius of a cylinder which will clear the bed, but quite often the swing of a lathe is quoted and this refers to the diameter of such a cylinder. Whichever way the size is expressed, it must be remembered that the work has to clear the lathe carriage when turningbetween centers. The bed length of a lathe does not indicate its capacity which is quoted as length between centers.Work Holding and Driving ChucksEvery lathe should be equipped with two chucks, one a self-centring (SC) 3-jaw chuck and the other a 4-jaw independent chuck, both of the size recommended by the lathe manufacturer.Both types are used in many different machining operations on short work pieces which can be held in the chuck, whilst longer items can be supported on the tailstock center or a steady at the outer end. Long lengths of bar, can, of course, be passed right through the hollow spindle whilstgriped in the chuck.Self-centring chucks The 3-jaw SC chuck will automatically center rounds or hexagons, all jaws opening or closing together as the scroll is turned with the key. The jaws are matched to the scroll during manufacture and each is numbered so that it can be returned to its correct slotafter removal.For holding large diameter work, scroll chucks are supplied with spare sets of jaws with reversed steps. The jaws themselves cannot be reversed. To remove the jaws, the chuck is opened out until all three jaws can be withdrawn as they disengage from the scroll. Re-assembly with either set of jaws is done in the following manner: the scroll is turned as for opening and when the screw end as has disappeared from No. 1 slot, No.1 jaw is pressed home and engaged by closing the chuck. When the scroll end appears in No.2 slot, it is would back a little and No.2 jaw is pressed home and engaged with the scroll. This is repeated for No.3 jaw.SC chucks are also made with two, four and six jaws, and of these, only the 4-jaw chuck is likely to find uses in the school workshop as it will center square bar stockJaws with external steps can be used to hold large rings or tubes by opening them on to the inside of the work.Scroll (SC) chucks will center work with reasonable accuracy, but unless great care is taken,they will quickly be thrown out of truth, mainly by wear or straining of the scroll from over-tightening of from digging-in which throws heavy loads on jaws and scroll, especially if short work pieces are wrenched from the chuck. Chuck jaws should be removed at regular intervals for the cleaning of the scroll, the jaw teeth and the slides. Over-lubrication is not a good thing, since excess oil either will be thrown out or will form a destructive grindingcompound with any fine swarf.The effect of inaccurate centring can be nullified by planning chuck jobs so that all of the important operations are carried out at one setting of the work. Once the job is removed, it is difficult to get it running true again.Independent Jaw Chucks Whilst the 4-jaw independent chuck is indispensable for holding work of irregular shape and for off-centre turning, it can also be used for holding squares or rounds. Centring takes a little longer but it can be done very accurately using each individual jaw adjustment. The procedure for centring in the 4-jaw chuck is described under Chuck-work.Independent jaw chucks are supplied with only one set of jaws since these are reversible.Draw-in Collet Chuck. The draw-in collet provides a quick and accurate means of holding small parts for models, instrument- and clock making. Made of heat treated steel, the collet is in the form of a sleeve, bored to receive round, hexagon and square sections closely approximating to the bore size.The collet, split into three or more segments, is drawn into the lathe spindle with a threaded tube (draw-bar), the tapered end bears against a matching taper inside an adaptor or closer on the lathe spindle and the collet closes on to the work. Because of its restricted range ofadjustment, it becomes necessary to hold one collet for each size and section of bar likely to bemachined and this could mean a large number.Multiblade collet chuck. The Multiblade collet consists of a steel body carrying six spring loaded blades arranged radially. When the collet is pushed into a conical housing,the blades move in with a parallel grip with a range of movement of more than 3 mm. On releasing the pressure, the springs retract the blades, allowing them to move forwards, releasing the work.With this large range of adjustment, fewer collets will be required and a total of twenty will hold any size of bar between 1.5 mm and 62 mm, round of hexagon. These collets are part of an integrated system of work holders in which any one collet can be used in a range of closing devices which include:(1) Key operated chucks for lathe work;(2) Lever or power operated chucks which can be opened or closed whilst the machine is running.There are also vertical mounting chucks for use in milling machines and drill or tool holders for use on capstan and automatic lathes.In a key-operated chuck the key rotates the tightening sleeve on its ball-race. The thread on the inside of this ring draws back the closing ring which is prevented from turning by means of the guide key. This closing ring draws the collet back into the conical housing, closing the blades.Chuck MountingsFor many years, the normal method of mounting a chuck on the spindle-nose has been by means of thread and register on the spindle, on to which screws a back-plate. The chuck, in its turn is bolted to the back- plate. In its initial assembly, the back-plate is screwed on to the spindle-nose and is then faced and finished dead to size to fit into a recess formed in theback of the chuck. The two are then screwed together and from then on, that chuck and backplate belong to that particular lathe. Attention is drawn to the plain-shouldered portion (register) which centers the chuck. This mounting exhibits several undesirable features and there is an increasing trend for chucks to be mounted directly on to spindles made to various international Standards Specifications. The advantages which these spindle-nose forms offerare:(1) the register is quite positive and is not subject to the wear which takes place when chucks are screwed on to the spindle;(2) the chuck is held very securely with no danger of its running off when the lathe is stopped (even when the spindle is fitted with a brake);(3) the overhang is reduced and with the chuck much closer to the bearings, the whole assembly is much more rigid, making for better work;(4) the chuck is quickly mounted and removed, except with the type where the chuck is bolted to a flange in a semi-permanent mounting.Whatever form of mounting is used, it is very important that both spindle and chuck registers and threads are quite clean before assembly. When removing chucks, the operator should always be ready to take the weight which comes suddenly, to avoid damage to lathe bed or fingers. A softwood block, resting on the lathe bed is good accident prevention here.Face-plateThis accessory is used for mounting work of awkward shapes which cannot readily be chucked.Catch-plateThe catch-plate, mounted on the lathe spindle is commonly used to drive work between centers, a driving pin engaging with a carrier (or dog) which screws on to the end of the work. Catch-plates are often made with a radial slot across the face so that the driving pin removed, a bent-tail carrier can then be used for driving the tail engaging in the slot.Lathe CentersThese are commonly made from high-speed steel and are hardened, but in fact, it is not Esse ntial for the live center (in the spindle) to be hardened as thereis no rubbing. Tailstock centers are also made with cemented carbide tips which give long and arduous service. Centers are accurately ground to standard tapers with the points usually finished to an included angle of 60 degree. The live center is adapted to the spindle socket by means of a taper sleeve.It is of the utmost importance that the centers fit perfectly in the spindle and tailstock barrel and before insertion they should be wiped clean and inspected for damage, the slightest burring of the tapers causing them to run out of truth.The spindle and tailstock tapers also require attention and cleaning should be done with a rag on a stick (not the finger) and never with the spindle revolving. The tailstock center is removed by retracting the barrel and when it is almost home, the end of the screw will eject the center. The tailstock center-point will require lubrication because the work is turning and its adjustment up to the work must be made carefully so that all end-float is eliminated without anyundue pressure which will heat and expand under heavy cutting and will bind on the center and damage it if the pressure is not relieved by a re-adjustment. Long bars will almost certainly show enough expansion to cause binding with only a slight rise in temperature and the adjustment and lubrication of the center must be watched carefully.Live Tailstock CenterThe use of live (revolving) tailstock center eliminates friction (but not work expansion).Other kinds are made for different conditions of service and with various point forms,including conical adaptors for centring tubes. The center rotates on precision bearings which take radial and thrust loads and elaborate precautions are taken to prevent the ingress of swarf or coolant. The bearings are lubricated for life and the unit should never require dismantling.Half center The use of a half center facilitates the end-facing of work between centers by allowing the tool to be fed right in. For end-facing with a normal center, the tool tip must be ground back at a little less than 60 degree.The truing of centers At the first signs of wear, center points must be retrued and this can be done with a tool-post grinder (a small, self contained grinding machine), mounted on the top slide which is set over at 30. With the center rotating slowly in the headstock, the grindstone is traversed, slowly, back and forth along the cone, taking only the very lightest of cuts. When the best possible finish has been achieved with the grinder, the cone can be given ahigh finish by honing with a perfectly flat stone. Lathe bed and slides are kept covered during grinding to keep all abrasive grit away.Technical English Through Reading Carriage StopThis is a very useful device for halting the carriage at predetermined points along the bed and can be used for the repeated finishing of parts of identical. Graduated DialsThe cross- and top-slide hand wheels are fitted with graduated dials giving accurate indications of slide movement in setting the depth of cuts. The dial is in the form of a collar which rotates with the hand wheel, usually through a frictiondrive which allows of its independent rotation. This enables one to set the depths of cuts from a zero reading by turning the dial and without altering the tool position. Dial graduations are read against a zero line scribed on the slide body.It must always be remembered that any adjustment of the cross slide will be doubled off the work diameter unless the lathe is fitted with a direct reading dial which shows the amount taken off the diameter.Because of market requirements, UK manufactures now supply lathes which operate in (1)metric terms only, i.e. with metric pitch lead screw and with dials reading in millimeters (to0.02 mm), (2) English terms only, i. e. With English pitch lead screw and dials reading to 0.001 ins, or (3) combinations of both, e.g. English pitch lead screw with dials reading in millimeters or with dual reading dials which give inch or metric reading as required.Dual reading dials have been developed to cope with metrication in the UK. These dials can be fitted as standard equipment on new machines or can be fitted to machines already in use.They are designed for single reading, i.e. when set to read metric, only inch graduations are visible and when set to read metric, only metric graduations are visible. The conversion, which is instantaneous, is brought about by sliding the thimble in or out, a system of sun and planet wheels giving precise conversions from inches to millimeters.Tool PostsThe American ring and rocker post is shown holding a tipped tool but it can be used for tool holders. Tools are quickly adjusted at center height by moving the rocker which beds on the loose ring. The four-way post is more suited to repetition work where a cycle of operations is to be performed, but nevertheless, it will be of occasional use in the school workshop. a modern slotted-block tool post dispenses with the need for packings to set the tool-height,this adjustment being made by means of a knurled screw. The tool, still in its holder,can be quickly removed for sharpening and no adjustment is needed when it is replaced in the post.Lathe ToolsHowever good a lathe may be, its efficient operation and the quality of the finish on its products will be dependent on the tools used. Apart from the actual shape of the tool point, the material of which it is made is of prime importance, the essential qualities being toughness which enables it to withstand shock and heavy pressure, and hardness which enables it to hold a cutting-edge. Although carbon tool steel has these properties when properly heat-treated, itsapplications are limited and it has been largely replaced by the high-speed steels and other alloys which retain a cutting-edge for much longer periods and under much more rigorous conditions, viz. : heavy cuts at elevated temperatures without losing their hardness. The air hardening property of high-speed steel which can be used on hard materials. The other alloys referred to are non-ferrous, they are extremely hard and brittle (and expensive) and are used in the form of tips which are brazed or butt welded on to shanks, often of high tensile steel. Tippedtools are also made with expendable tips which are held in place with a small clamp and when dull, the tip is discarded and replaced with a new one. Stellite (an alloy of cobalt, chromium and tungsten) is used in making tips and the hardest are made from the cemented carbides (for example, tungsten carbide). All permit of cutting-speeds well in excess of those possible withhigh-speed steels.Lathe tools can be divided into four groups:(1) Solid (one-piece) tools of carbonor high-speed steel, gripped directly in the tool post;(2) Tool holder bits of high speed steel and of square or round section. Held in tool holders;(3) Tipped tools of various kinds;(4) Special tools, e.g. boring tools, boring bars which hold tool bits, dee bits, form tools of various kinds and knurling tools.Tool AnglesThe wedge form of the cutting part of a lathe tool involves two components, viz, clearance below the cutting edge, without which the tool could only rub on the work, and rake which is the slope on the face, away from the cutting edge. Whilst clearance varies only slightly for different purposes, rake shows marked variations, being adjusted to suit the metal being turned. The direction of rake is determined mainly by feed direction and the shape of the cutting edge.ClearanceClearance, formed on both the major and minor flanks of the tool is kept as small as possible, consistent with the proper working of the tool. Excessive clearance reduces support for the cutting edge and increases the tendency to chatter. In addition to the slight variations in clearance for different metals, there are several cases where further adjustments are required,viz:(1) Because of the convex face of the work in turning, front-cutting tools will operate with slightly reduced clearance, but not for surfacing cuts;(2) For traversing cuts, the correct clearance may need to be increased slightly because the helical form of the transient surface becomes more pronounced, unless the feed speed is reduced;(3) Boring tools will require increased clearance to avoid rubbing on the concave work surface. A second flank will provide relief at the heel and with very small bores, this secondary angle may have to be quite large.Rake and Cutting Actiontools for brittle metals like hard brass and castiron, are formed with little or no rake, the near-flat face presented to the work causing the waste metal to shear and break away in small chips. Where the metal forms a flowing chip (and many metals do this), the tool must be given rake because the waste metal cannot be forced off by shearing, but must be lifted off by the wedge action of the tool. Chip pressure is very considerable when heavy cuts are taken and tool cutting parts weakened by excessive rake or clearance will be prone to chatter and to digging in caused bythe feeding in effect of pressure on sloping face.Rake should produce the smallest possible chipdeflection whilst leaving the cutting part stiff enough to withstand the load without springing. For very hard metals rake is quite small, e.g. , about 10 for tool steel, increasing to 30 or more for soft and ductile metalslike copper and aluminum.In Figure 2-5 are seen examples showing how rake direction influences the line of chip flow from the transient surface. Whilst this is an important feature in tool designing. There are also other factors to be considered.Tool GeometryThe geometry of the parting off tool is probably the least complicated and though shown in Figure 2-6 with the major cutting edge perpendicular to the toolaxis, it is usually formed at a small angle to give a clean break through. For the tool shown in Figure 2-5,the direction of feed motion aligns with the plane of normal rake and with the tool set horizontally in thelathe, there is a simple and obvious relationship between tool angles and surfaces both in its makingFIG. 2-5 Rake feed direction and Chip-flow and in its operation.Tools, however, are produced with the cutting edges in a variety of orientations and when in use, the tool shank may be set at any angle in relationto the work surface. the angles thus formed by tool cutting edges, faces and flanks relative to the resultant cutting direction and tothe work surfaces are known as working angles which are not always readily oriented or measured in the making or the re-grinding of the tool.The recommendations of the British Standards Institution in resolving these problems involve the use of two systems of reference planes through a selected point on the cutting edge by means of which tool angles and working angles can be defined. The first, known as the tool-in-hand system defines the geometry of a tool to facilitate its manufacture whilst the other, known as the tool-in-use system, defines the effective tool geometry when it is performing a cutting operation.The nomenclature for defining rake, clearance and other cutting tool angles is known as the normal rake system and it is the preferred system replacing the former maximum rake system.It is not possible to go further into this subject within the context of this book and the readerwho seeks further information is advised to refer to the British Standards publication BS 1296 Part 2, Glossary of Terms for Single Point Tools. Cutting SpeedsCutting speeds are usually expressed in terms of meters per minute and the speeds at which the tool should pass over the work to produce the best results at suitable speeds. Cutting speeds are governed by two factors:(1) The hardness of the metal being cut;(2) The type of tool being used, HSS and tipped tools operating at much higher speeds than carbon steel tools.To maintain these speeds, small diameter work will have to turn much faster than larger diameters.SteadiesTwo kinds of steady are used for supporting long work against the pressure of the tool. The fixed steady is secured to the lathe bed whilst the travelling steady is mounted on the carriage and moves along the work behind the tool, as each cut is taken. The fixed steady can be used to support the end of a bar, gripped in the chuck, for end-facing, for center drilling, for boring orfor threading. LATHEWORKTurning on Centers The Center DrillThe first operation in the turning of work between centers is the drilling of the holes for mounting the work, and for this, the combined drill and countersink (center drill) is used. Three types of drill are made (A, B and R), but only the double-ended type A is considered here.The hole at the bottom of the countersinking leaves clearance for the lathe center point and provides a reservoir for lubricant. When center drilling in the lathe, the bar can be passed through the spindle if not too large and held in the 3-jaw chuck. The appropriate cutting fluid should be used and the drill must not be bumpedagainst the work or forced as this might cause the point to split and break off in the work. If the bar is too large for the spindle bore, it can begripped in a chuck with the free end supported in a fixed steady. When a bar has to be finishedto length between centers, the allowance for machining should not be excessive, otherwise thebearing surfaces on the centers will become too slight when the facing is done.Turning ExampleA piece of work for turning on centers is shown in Figure 2-7 with suggestions for theoperations involved. The bar should be cut off long enough to allow for a carrier
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