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机械零件制图识图必须懂的七大基础知识
一. 零件图的内容
1. The content of the part drawing
1）标题栏：位于图中的右下角，标题栏一般填写零件名称、材料、数量、图样的比例，代号和图样的责任人签名和单位名称等。标题栏的方向与看图的方向应一致。
1) title bar: in the bottom right corner of the picture, the title bar generally fill in the parts name, material, quantity, pattern proportion, code number and the responsible person's signature and unit name of the drawing. The direction of the title bar should be in accordance with the direction of the picture.
2）一组图形：用以表达零件的结构形状，可以采用视图、剖视、剖面、规定画法和简化画法等表达方法表达。
2) a group of graphics: used to express the structure and shape of the parts, which can be expressed by means of view, profile, section, prescribed painting and simplified drawing.
3）必要的尺寸：反映零件各部分结构的大小和相互位置关系，满足零件制造和检验的要求。
3) necessary size: reflect the size and mutual position of parts of parts and meet the requirements of parts manufacturing and inspection.
4）技术要求：给出零件的表面粗糙度、尺寸公差、形状和位置公差以及材料的热处理和表面处理等要求。
4) technical requirements: the surface roughness of the parts, dimensional tolerance, shape and position tolerances, and the heat treatment and surface treatment of the material.
二. 视图
Two. View
基本视图:物体向６个基本投影面(物体在立方体的中心，投影到前后左右上下6个方向)投影所得的视图:
Basic view: the object is projected to 6 basic projection surfaces (the object is in the center of the cube, projecting to the 6 directions in the upper and the right and lower sides).
三. 全剖半剖
Three. Full profile half section
全剖视图：用剖切
Full section view: dissection
的剖开物体所得到的剖视图称为全剖试图：
The sectional view obtained by a caesarean section is called a full section attempt.
半剖视图：当物体具有对称平面时，向垂直于对称平面的投影面上投影所得的图形，可以对中心线为界，一半画成剖视图，另一半画成视图，称为半剖视图：
Half sectional view: when the object has a symmetrical plane, it can be projected on the projection plane perpendicular to the symmetric plane. It can be bounded on the center line, half cut into a sectional view, and the other half as a view, called a half sectional view.
四. 尺寸及其标注
Four. Size and its annotation
1、尺寸的分类
1, the classification of size
1）基本尺寸：通过它应用上、下偏差可计算出极限尺寸的尺寸。
1) basic size: it can calculate the size of the limit size by using the upper and lower deviations.
2）实际尺寸：通过测量获得的尺寸。
2) actual size: the size obtained by measuring.
3）极限尺寸：一个尺寸允许的两个极端，其中最大的一个称为最大极限尺寸；较小的一个称为最小极限尺寸。
3) limit size: one size allowed two extremes, of which the largest one is called the maximum limit size; the smaller one is called the minimum limit size.
4）尺寸偏差：最大极限尺寸减其基本尺寸的所得的代数差称为上偏差；最小极限尺寸减其基本尺寸所得代数差称为下偏差。上下偏差统称为极限偏差，偏差可正可负。
4) size deviation: the algebraic difference between the maximum limit size and the basic size is called the upper deviation, and the minimum limit size minus its basic size is called the lower deviation. The upper and lower deviations are called limit deviations, and the deviations can be negative.
5）尺寸公差：简称公差 最大极限尺寸减去最小极限尺寸之差，它是允许尺寸的变动量。尺寸公差永为正值。
5) dimensional tolerance: the difference between the maximum limit size of the tolerance and the minimum limit size, which is the amount that allows the size to be changed. The dimensional tolerance is always positive.
6）零线：在极限与配合图中，表示基本尺寸的一条直线，以其为基准确定偏差和公差。
6) zero line: a straight line representing the basic size in the limit and match diagram to determine the deviation and tolerance on the basis of the zero line.
7)标准公差：极限与配合制中，所规定的任一公差。国家标准中规定，对于一定的基本尺寸，其标准公差共有20个公差等级。
7) standard tolerances: any tolerances specified in the limit and coordination system. The national standard stipulates that, for a certain basic dimension, there are 20 tolerance levels for its standard tolerances.
公差分为CT 、IT、 JT 3个系列标准。CT系列为铸造公差标准， IT是ISO国际尺寸公差，JT为中国机械部尺寸公差
The tolerances are divided into 3 series of standards: CT, IT and JT. The CT series is a casting tolerance standard, IT is ISO international dimension tolerance, and JT is the dimensional tolerance of the Chinese Machinery Department
不同产品不同的公差等级。等级越高，生产技术要求越高，成本越高。
Different tolerance grades for different products. The higher the level, the higher the production technology and the higher the cost.
8)基本偏差：在极限与配合制中，确定公差带相对零线位置的那个极限偏差，一般为靠近零线的那个偏差。国家标准中规定基本偏差代号用拉丁字母表示，大写字母表示孔，小写字母表示轴，对孔和轴的每一个基本尺寸段规定了28个基本偏差。
8) basic deviation: in the limit and coordination system, the limit deviation, which determines the relative zero line position of the tolerance zone, is generally the deviation from the zero line. In the national standard, the basic deviation code is written in Latin letters. The capital letters denote the holes and the lowercase letters indicate the axes, which stipulates 28 basic deviations for each basic length segment of the hole and the shaft.
3、尺寸的标注
3, dimensioning
尺寸基准
Dimension datum
尺寸基准是标注定位尺寸的基准，尺寸基准一般分为设计基准(设计时用以确定零件结构位置)和工艺基准(制造时用以定位、加工和检验)。
The dimension datum is the benchmark for dimensioning the location. Generally, the dimension datum is divided into the design datum (the design part is used to determine the part structure location) and the process datum (when manufacturing is used to locate, process and check).
尺寸基准又分为主要基准和辅助基准。一般在长、宽、高三个方向各选一个设计基准为主要基准，它们决定零件的主要尺寸，主要尺寸要从主要基准直接注出。除主要基准之外的其余的尺寸基准则为辅助基准。
The size datum is divided into the main datum and the auxiliary datum. At length, width and height directions of each selected a design reference as the reference, the main parts of the size of their decisions, mainly from the main datum directly outjection size. In addition to the main benchmark, the rest of the size benchmarks are auxiliary benchmarks.
五. 公差与配合
Five. Tolerance and coordination
1、公差
1. Tolerance
为了保证零件的互换性，设计时根据零件的使用要求而制定的允许尺寸的变动量，称为尺寸公差，简称公差。公差的数值愈小,即允许误差的变动范围越小,则越难加工。
In order to ensure the interchangeability of parts, the amount of allowable dimensions, called dimensional tolerances, is called tolerance for short, according to the requirements of the use of the parts. The smaller the value of the tolerance, the smaller the range of allowable errors, the harder it is to work.
2、形状和位置公差（简称形位公差）的概念
2. The concept of shape and position tolerance (abbreviated form tolerance)
1）经过加工的零件表面，不仅有尺寸误差，同时也产生形状和位置误差。这些误差不但降低了零件的精度，同时也会影响使用性能。因此，国家标准规定了零件表面的形状和位置公差，简称形位公差。
1) the surface of the processed parts not only has the size error, but also the error of the shape and position. These errors not only reduce the precision of the parts, but also affect the performance. Therefore, the national standard stipulates the tolerance of the shape and position of the surface of the parts, for short, the tolerance of the shape and position.
2）尺寸公差在零件图的注法
2) the injection method of the dimensional tolerance in the part drawing
在零件图中的标注尺寸公差常用标注极限偏差值，如图
In the part drawing, the dimensioning tolerance is often used as the marking limit deviation value, such as drawing
3）框格形位公差的要求在框格中给出，框格由两格或多格组成。框格中的内容从左 到右按下列次序填写： 公差特征符号，公差值，需要时用一个或多个字母表示基准要素或基准体系。
3) frame shape and position tolerances are required in the frame, the frame is composed of two or more. The contents of the frame from left to right according to the following order: fill out the geometric characteristic symbol, tolerance, need to use one or more letters or datum reference system.
4)被测要素
4) the measured elements
用带箭头的指引线将被测要素与公差框格一端相连，指引线箭头指向公差带的宽度方向或直径方面。指引线箭头所指部位可有：
With the lead of the measured elements and tolerances frame is connected with one end with an arrow, the arrow pointing to the lead width or diameter tolerance zone. The point refers to the position of the lead arrow.
（1）当被测要素为整体轴线或公共中心平面时，指引线箭头可直接指在轴线或中心线上，如下图左。
(1) when the measured elements are the overall axis or the public center plane, the lead arrow can directly refer to the axis or the center line, as follows.
（2）当被测要素为轴线、球心或中心平面时，指引线箭头应与该要素的尺寸线对齐，如下图中。
(2) when the measured elements for the axis or center plane and the center, which lead the arrow should be aligned with the size of the line elements, as shown in.
（3）当被测要素为线或表面时，指引线箭头应指要该要素的轮廓线或其引出线上，并应明显地与尺寸线错开，如下图右
(3) when the measured elements of a line or surface, which leads to the arrow should be contour elements or the outgoing line, and should clear away from the dimension line, below the right
5)基准要素
5) benchmark elements
用带基准符号的指引线将基准要素与公差框格的另一端相连，如下图左。
With reference symbols refers to the other end connected to the lead base elements and tolerances below left sash.
（1）当基准要素为素线或表面时，基准符号应靠近该要素的轮廓线或引出线标注，并应明显地与尺寸线箭
(1) when the reference element is a plain line or surface, the reference symbol should be close to the outline of the element or the drawing line, and should be marked with the dimension line.
1. The content of the part drawing
1）标题栏：位于图中的右下角，标题栏一般填写零件名称、材料、数量、图样的比例，代号和图样的责任人签名和单位名称等。标题栏的方向与看图的方向应一致。
1) title bar: in the bottom right corner of the picture, the title bar generally fill in the parts name, material, quantity, pattern proportion, code number and the responsible person's signature and unit name of the drawing. The direction of the title bar should be in accordance with the direction of the picture.
2）一组图形：用以表达零件的结构形状，可以采用视图、剖视、剖面、规定画法和简化画法等表达方法表达。
2) a group of graphics: used to express the structure and shape of the parts, which can be expressed by means of view, profile, section, prescribed painting and simplified drawing.
3）必要的尺寸：反映零件各部分结构的大小和相互位置关系，满足零件制造和检验的要求。
3) necessary size: reflect the size and mutual position of parts of parts and meet the requirements of parts manufacturing and inspection.
4）技术要求：给出零件的表面粗糙度、尺寸公差、形状和位置公差以及材料的热处理和表面处理等要求。
4) technical requirements: the surface roughness of the parts, dimensional tolerance, shape and position tolerances, and the heat treatment and surface treatment of the material.
二. 视图
Two. View
基本视图:物体向６个基本投影面(物体在立方体的中心，投影到前后左右上下6个方向)投影所得的视图:
Basic view: the object is projected to 6 basic projection surfaces (the object is in the center of the cube, projecting to the 6 directions in the upper and the right and lower sides).
三. 全剖半剖
Three. Full profile half section
全剖视图：用剖切
Full section view: dissection
的剖开物体所得到的剖视图称为全剖试图：
The sectional view obtained by a caesarean section is called a full section attempt.
半剖视图：当物体具有对称平面时，向垂直于对称平面的投影面上投影所得的图形，可以对中心线为界，一半画成剖视图，另一半画成视图，称为半剖视图：
Half sectional view: when the object has a symmetrical plane, it can be projected on the projection plane perpendicular to the symmetric plane. It can be bounded on the center line, half cut into a sectional view, and the other half as a view, called a half sectional view.
四. 尺寸及其标注
Four. Size and its annotation
1、尺寸的分类
1, the classification of size
1）基本尺寸：通过它应用上、下偏差可计算出极限尺寸的尺寸。
1) basic size: it can calculate the size of the limit size by using the upper and lower deviations.
2）实际尺寸：通过测量获得的尺寸。
2) actual size: the size obtained by measuring.
3）极限尺寸：一个尺寸允许的两个极端，其中最大的一个称为最大极限尺寸；较小的一个称为最小极限尺寸。
3) limit size: one size allowed two extremes, of which the largest one is called the maximum limit size; the smaller one is called the minimum limit size.
4）尺寸偏差：最大极限尺寸减其基本尺寸的所得的代数差称为上偏差；最小极限尺寸减其基本尺寸所得代数差称为下偏差。上下偏差统称为极限偏差，偏差可正可负。
4) size deviation: the algebraic difference between the maximum limit size and the basic size is called the upper deviation, and the minimum limit size minus its basic size is called the lower deviation. The upper and lower deviations are called limit deviations, and the deviations can be negative.
5）尺寸公差：简称公差 最大极限尺寸减去最小极限尺寸之差，它是允许尺寸的变动量。尺寸公差永为正值。
5) dimensional tolerance: the difference between the maximum limit size of the tolerance and the minimum limit size, which is the amount that allows the size to be changed. The dimensional tolerance is always positive.
6）零线：在极限与配合图中，表示基本尺寸的一条直线，以其为基准确定偏差和公差。
6) zero line: a straight line representing the basic size in the limit and match diagram to determine the deviation and tolerance on the basis of the zero line.
7)标准公差：极限与配合制中，所规定的任一公差。国家标准中规定，对于一定的基本尺寸，其标准公差共有20个公差等级。
7) standard tolerances: any tolerances specified in the limit and coordination system. The national standard stipulates that, for a certain basic dimension, there are 20 tolerance levels for its standard tolerances.
公差分为CT 、IT、 JT 3个系列标准。CT系列为铸造公差标准， IT是ISO国际尺寸公差，JT为中国机械部尺寸公差
The tolerances are divided into 3 series of standards: CT, IT and JT. The CT series is a casting tolerance standard, IT is ISO international dimension tolerance, and JT is the dimensional tolerance of the Chinese Machinery Department
不同产品不同的公差等级。等级越高，生产技术要求越高，成本越高。
Different tolerance grades for different products. The higher the level, the higher the production technology and the higher the cost.
8)基本偏差：在极限与配合制中，确定公差带相对零线位置的那个极限偏差，一般为靠近零线的那个偏差。国家标准中规定基本偏差代号用拉丁字母表示，大写字母表示孔，小写字母表示轴，对孔和轴的每一个基本尺寸段规定了28个基本偏差。
8) basic deviation: in the limit and coordination system, the limit deviation, which determines the relative zero line position of the tolerance zone, is generally the deviation from the zero line. In the national standard, the basic deviation code is written in Latin letters. The capital letters denote the holes and the lowercase letters indicate the axes, which stipulates 28 basic deviations for each basic length segment of the hole and the shaft.
3、尺寸的标注
3, dimensioning
尺寸基准
Dimension datum
尺寸基准是标注定位尺寸的基准，尺寸基准一般分为设计基准(设计时用以确定零件结构位置)和工艺基准(制造时用以定位、加工和检验)。
The dimension datum is the benchmark for dimensioning the location. Generally, the dimension datum is divided into the design datum (the design part is used to determine the part structure location) and the process datum (when manufacturing is used to locate, process and check).
尺寸基准又分为主要基准和辅助基准。一般在长、宽、高三个方向各选一个设计基准为主要基准，它们决定零件的主要尺寸，主要尺寸要从主要基准直接注出。除主要基准之外的其余的尺寸基准则为辅助基准。
The size datum is divided into the main datum and the auxiliary datum. At length, width and height directions of each selected a design reference as the reference, the main parts of the size of their decisions, mainly from the main datum directly outjection size. In addition to the main benchmark, the rest of the size benchmarks are auxiliary benchmarks.
五. 公差与配合
Five. Tolerance and coordination
1、公差
1. Tolerance
为了保证零件的互换性，设计时根据零件的使用要求而制定的允许尺寸的变动量，称为尺寸公差，简称公差。公差的数值愈小,即允许误差的变动范围越小,则越难加工。
In order to ensure the interchangeability of parts, the amount of allowable dimensions, called dimensional tolerances, is called tolerance for short, according to the requirements of the use of the parts. The smaller the value of the tolerance, the smaller the range of allowable errors, the harder it is to work.
2、形状和位置公差（简称形位公差）的概念
2. The concept of shape and position tolerance (abbreviated form tolerance)
1）经过加工的零件表面，不仅有尺寸误差，同时也产生形状和位置误差。这些误差不但降低了零件的精度，同时也会影响使用性能。因此，国家标准规定了零件表面的形状和位置公差，简称形位公差。
1) the surface of the processed parts not only has the size error, but also the error of the shape and position. These errors not only reduce the precision of the parts, but also affect the performance. Therefore, the national standard stipulates the tolerance of the shape and position of the surface of the parts, for short, the tolerance of the shape and position.
2）尺寸公差在零件图的注法
2) the injection method of the dimensional tolerance in the part drawing
在零件图中的标注尺寸公差常用标注极限偏差值，如图
In the part drawing, the dimensioning tolerance is often used as the marking limit deviation value, such as drawing
3）框格形位公差的要求在框格中给出，框格由两格或多格组成。框格中的内容从左 到右按下列次序填写： 公差特征符号，公差值，需要时用一个或多个字母表示基准要素或基准体系。
3) frame shape and position tolerances are required in the frame, the frame is composed of two or more. The contents of the frame from left to right according to the following order: fill out the geometric characteristic symbol, tolerance, need to use one or more letters or datum reference system.
4)被测要素
4) the measured elements
用带箭头的指引线将被测要素与公差框格一端相连，指引线箭头指向公差带的宽度方向或直径方面。指引线箭头所指部位可有：
With the lead of the measured elements and tolerances frame is connected with one end with an arrow, the arrow pointing to the lead width or diameter tolerance zone. The point refers to the position of the lead arrow.
（1）当被测要素为整体轴线或公共中心平面时，指引线箭头可直接指在轴线或中心线上，如下图左。
(1) when the measured elements are the overall axis or the public center plane, the lead arrow can directly refer to the axis or the center line, as follows.
（2）当被测要素为轴线、球心或中心平面时，指引线箭头应与该要素的尺寸线对齐，如下图中。
(2) when the measured elements for the axis or center plane and the center, which lead the arrow should be aligned with the size of the line elements, as shown in.
（3）当被测要素为线或表面时，指引线箭头应指要该要素的轮廓线或其引出线上，并应明显地与尺寸线错开，如下图右
(3) when the measured elements of a line or surface, which leads to the arrow should be contour elements or the outgoing line, and should clear away from the dimension line, below the right
5)基准要素
5) benchmark elements
用带基准符号的指引线将基准要素与公差框格的另一端相连，如下图左。
With reference symbols refers to the other end connected to the lead base elements and tolerances below left sash.
（1）当基准要素为素线或表面时，基准符号应靠近该要素的轮廓线或引出线标注，并应明显地与尺寸线箭
(1) when the reference element is a plain line or surface, the reference symbol should be close to the outline of the element or the drawing line, and should be marked with the dimension line.
