机械图纸中常见的符号及意义《机械识图》根据最新的中等职业学校机械制图教学大纲，针对中等职业学校学生在识图知识与技能方面的就业需求编写而成，注重对中等职业学校学生的识图能力培养。

《图文对半，直观形象，方便教学。

全书共分9个项目：抄画平面图形，三视图的形成与投影作图，基本几何体的视图，绘制与识读组合体视图，识读视图、剖视图和断面图，识读轴套类零件图，识读盘盖轮类零件图，识读叉架类和箱壳类零件图，识读装配图。

通过这9个项目将知识点与任务有机地结合，由浅入深，循序渐进，使学生完成技能的训练，达到学以致用的目的。

自劳动开创人类文明史以来,图形与语言、文字一样,是人们认识自然、表达和交流思想的基本工具,在图学发展的历史长河中,经过不断地完善和发展得到了广泛的应用。

在现代工业生产中,机械、化工或建筑都是根据图样进行制造和施工的。

设计者通过图样表达设计意图;制造者通过图样了解设计要求、组织制造和指导生产;使用者通过图样了解机器设备的结构和性能,进行操作、维修和保养。

因此机械图样是交流传递技术信息、思想的媒介和工具,是工程界通用的技术语言。

作为职业技术教育培养目标的生产第一线的现代新型技能型人才,必须学会并掌握这种语言,具备识读和绘制机械图样的基本能力。

从以下几方面可以体现其重要性:从事机械制造行业就须掌握机械制图 ,学习机械制图感到抽象、困难,其原因之一是习惯于在平面上思考问题,缺乏空间思维能力。

在学习过程中教师要有针对性地借助各种媒体,直观、形象地引导学生建立起空间概念,由平面思维转换到空间思维。

把物体的投影与实际零件结构紧密联系,不断地“由物画图”和“由图画物”,既要想象物体的形状,又要思考图形间的投影规律,步提高空间想象和思维能力。

有了这种能力,在实际工作时,才会通过二维的平面图——零件图(或装配图)想象出来三维的空间物体——实际零件(装配体),只有掌握这种技能,才能顺利完成零件加工或机器装配的工作。

所以,空间想象能力是学习机械制图的核心内容。

《机械制图》的基本原理,制图标准、及相关规则,严肃体现出国家标准的统一性,无论谁都必须严格遵照执行。

随着我国各个领域与国际接轨的今天,在机械制造行业,国家标准与国际标准也会逐步一致,使我国机械制造行业技术人才能更好的与之交流,那么就必须熟练地掌握这门技术语言,更便于同行业间进行技术探讨和技术革新,但是前提条件是必须精通机械制图这门课程以及相关的国家标准,并且反复强调标准规定的严谨性、权威性和法制性,使技术人员较好地确立标准化意识。

机械制图对解决实际问题和创新能力的影响《机械制图》课除了如何使他们很好地建立空间想象能力、掌握投影规律及国家标准,还必须具有机械专业的相关知识,如金属工艺学、机械制造工艺学、机械零件与机械原理、公差配合与技术测量等,这些知识在机械制图中的零件结构、表面质量、加工方法、材料选择、技术要求、连接装配关系等方面都要用到。

也不是只局限于了解制图上的一些概念、定义和规则,还会学习和掌握到其它相关领域的各种知识,并且会正确、合理、全面地应用好机械制图这门工具,是现代化生产中技术人才最基本的要求,通过机械制图的学习,就要求具备这种让机械制图与实际结合起来,解决实际工作中存在的各方面的问题的能力。

《机械制图》是人们进行技术革新、技术改造的工具,是对新设计、新构思、新工艺研究探索,反映和表达高新技术、发明创造新生事物的载体。

大胆地在该课程教学中融进新思想、新设计、探索和创新,是知识经济时代向我们提出的新课题、新挑战。

我们在教学全过程中始终注意贯彻这一主导思想。

激励大家勤于动脑,勇于探索,敢于创新,逐步形成了创新观念,创新意识,培养了学生的创新思维能力。

如此较长时间,多个阶段的激发培养,让学生对《机械制图》课程的知识点,发生飞跃的认识,培养起创造能力与个性品质,在今后实际生产中进行技术革新、机械设计时起到要作用。

在加工制造中零件图和装配图的作用 ,任何一台机器或一个部件都是由若干零件装配而成的,制造机器首先要依据零件图加工零件,再根据装配图,组装成机器或者部件。

零件图是制造和检验零件的主要依据,不会识读零件图,根本无从着手加工零件,所以,识读零件图和绘制零件图是《机械制图》的重要内容。

能快速而正确地识读零件的图纸,理解零件的加工信息,是正确实施零件加工的前提,能合理表达零件的结构,正确规范的绘制一张零件的图纸,是在职业岗位上进行技术交流和沟通的必要手段。

另外机器或者部件的设计过程中,一般先根据设计要求画出装配图以表达机器或者部件的工作原理、传动路线,零件之间的装配关系以及零件的结构形状,然后按照装配图设计零件,并绘制零件图。

再生产过程中,装配图又是制定机器或部件装配工艺规程、指导装配、检验、安装和维修的依据。

因此识读装配图是在生产交流和技术革新中重要的一项读图能力Straightness - a condition where an element of a surface or an axis is astraight line.Flatness - is the condition of a surface having all elements in one plane.Roundness - describes the condition on a surface of revolution (cylinder,cone, sphere) where all points of the surface intersected by any plane.Cylindricity - describes a condition of a surface of revolution in which allpoints of a surface are equidistant from a common axis.Profile of a Line - is the condition permitting a uniform amount of profile variation, ether unilaterally or bilaterally, along a line element of a feature.Profile of a Surface - is the condition permitting a uniform amount of profile variation, ether unilaterally or bilaterally, on a surface.All Around Symbol - indicating that a tolerance applies to surfaces all around the part.Angularity - is the condition of a surface, axis, or centerplane, which is at a specified angle from a datum plane or axis.Perpendicularity - is the condition of a surface, axis, or line, which is 90 deg. From a datum plane or a datum axis.Parallelism - is the condition of a surface, line, or axis, which is equidistant at all points from a datum plane or axis.Position Tolerance - defines a zone within which the axis or center plane of a feature is permitted to vary from true (theoretically exact) position.Concentricity - describes a condition in which two or more features , in any combination, have a common axis.Symmetry - is a condition in which a feature (or features) is symmetrically disposed about the center plane of a datum feature.Runout - is the composite deviation from the desired form of a part surface of revolution through on full rotation (360 deg) of the part on a datum axis.Total Runout - is the simultaneous composite control of all elements of a surface at all circular and profile measuring positions as the part is rotated through 360.Maximum Material Condition (MMC) - is that condition of a part feature wherein it contains the maximum amount ofmaterial within the stated limits of size. That is: minimum hole size and maximum shaft size.Least Material Condition (LMC) - implies that condition of a part feature of size wherein it contains the least (minimum) amount of material, examples, largest hole size and smallest shaft size. It is opposite to maximum material condition.Regardless Of Feature Size (RFS) - the condition where the tolerance of form, runout or location must be met irrespective of where the feature lies within its size tolerance.Projected Tolerance Zone - applies to a hole in which a pin, stud, screw, etc., is to be inserted. It controls the perpendicularity of the hole to the extent of the projection from the hole and as it relates to the mating part clearance. The projected tolerance zone extends above the surface of the part to the functional length of the pin, stud, and screw relative to its assembly with the mating part.Tangent Plane - indicating a tangent plane is shown. The symbol is placed in the feature control frame following the stated tolerance.Free State Variations - is a term used to describe distortion of a part after removal of forces applied during manufacture.Diameter - indicates a circular feature when used on the field of a drawing or indicates that the tolerance is diametrical when used in a feature control frame.Basic Dimension - used to describe the exact size, profile, orientation or location of a feature. A basic dimension is always associated with a feature control frame or datum target. (Theoretically exact dimension in ISO)Reference Dimension - a dimension usually without tolerance, used for information purposes only. It does not govern production or inspection operations. (Auxiliary dimension in ISO)Datum Feature - is the actual component feature used to establish a datum.Dimension Origin - Signifies that the dimension originates from the plane established by the shorter surface and dimensional limits apply to the other surface.Feature Control Frame - is a rectangular boxcontaining the geometric characteristics symbol,andthe form, runout or location tolerance. If necessary,datum references and modifiers applicable to thefeature or the datums are also contained in thebox.Conical Taper - is used to indicate taper for conical tapers. This symbol is always shown with the vertical leg to the left.Slope - is used to indicate slope for flat tapers. This symbol is always shown with the vertical leg to the left.Counterbore/Spotface - is used to indicate a counterbore or a spotface. The symbol precedes the dimension of the counterbore or spotface, with no spaceCountersink - is used to indicate a countersink. The symbol precedes the dimensions of the countersink with no space.Depth/Deep - is used to indicate that a dimension applies to the depth of a feature. This symbol precedes the depth value with no space in between.Square - is used to indicate that a single dimension applies to a square shape. The symbol precedes the dimension with no space between.Number of Places - the X is used along with a value to indicate the number of times a dimension or feature is repeated on the drawing.Arc Length - indicating that a dimension is an arc length measured on a curved outline. The symbol is placed above the dimension.Radius - creates a zone defined by two arcs (the minimum and maximum radii). The part surface must lie within this zone.Spherical Radius - precedes the value of a dimension or tolerance.Spherical Diameter - shall precede the tolerance value where the specified tolerance value represents spherical zone. Also, a positional tolerance maybe used to control the location of a spherical feature relative to other features of a part. The symbol for spherical diameter precedes the size dimension of the feature and the positional tolerance value, to indicate a spherical tolerance zone.tolerance zone defined by two arcs (the minimum and maximum radii) that are tangent to the adjacent surfaces. Where a controlled radius is specified, the part contour within the crescent-shaped tolerance zone must be a fair curve without flats or reversals. Additionally, radii taken at all points on the part contour shall neither be smaller than the specified minimum limit nor larger than the maximum limit.Between - to indicate that a profile tolerance applies to several contiguous features, letters may designate where the profile tolerance begins and ends. These letters are referenced using the between symbol (since 1994) or the word between on drawings made to earlier versions of the Standard.Statistical Tolerance - is the assigning of tolerances to related components of an assembly on the basis of sound statistics (such as the assembly tolerance is equal to the square root of the sum of the squares of the individual tolerances). By applying statistical tolerancing, tolerances of individual components may be increased or clearances between mating parts may be reduced. The increased tolerance or improved fit may reduce manufacturing cost or improve the product's performance, but shall only be employed where the appropriate statistical process control will be used. Therefore, consideration should be given to specifying the required Cp and /or Cpk or other process performance indices.Datum Target - is a specified point, line, or area on a partthat is used to establish the Datum Reference Plane formanufacturing and inspection operations.Target Point - indicates where the datum target point is dimensionally located on the direct view of the surface.。