Chapter2 Limit and Fits 极限与配合 Terms of Sizes 尺寸定义 Basic concept of limits and fits 极限与配合的基本概念 Standard tolerance and basic deviation 标准公差与基本偏差 Fitting 配合 Marking limits and fits 极限与配合的标注方法 Exercises 练 习 题

Hole and Shaft 孔和轴 Hole - designate all INTERNAL features of a part, including parts which are not cylindrical. Shaft - designate all EXTFRNAL features of a part, including parts which are not cylindrical.

Basic concept of limits and fits 极限与配合的基本概念 Basic size Nominal size specified in design. 基本尺寸 设计时给定的尺寸； (如Φ50 ) Φ50.005 (2) Actual size The size obtained by measuring; 实际尺寸 制造后的实际尺寸； (如Φ49.992 ) Φ50 Φ49.992 (3) Limit size The limit values of an allowed range that is the size of a part varies. 极限尺寸 允许实际尺寸变化的极限值； Maximum limit size 最大极限尺寸 Minimum limit size 最小极限尺寸 (如:Φ50.005 ) (如:Φ49.992 ) (4)Actual Size (Da, da): A measure size obtained from a finished part 实际尺寸 .

（5）Maximum Material Condition (MMC) and Maximum Material Size (MMS):最大实体状态和最大实体尺寸 the maximum material condition is a feature where contains the maximum amount of material within the stated limits of size 孔轴拥有材料量最多时的状态，该状态下的尺寸

Least Material Condition (LMC) and Least Material Size (LMS): 最小实体状态和最小实体尺寸 the least material condition is a feature where contains the least amount of material within the stated limits of size

2.2 Terms of Deviations and Tolerances 偏差和公差的术语 Φ50.005 ES 0.005 Φ50 Φ49.992 EI －0.008 (4) Size deviation Difference of a given size minus its basic size. 尺寸偏差 极限尺寸与基本尺寸之差值； Upper deviation 上偏差 ES孔/ es轴=最大极限尺寸-基本尺寸 Lower deviation 下偏差 EI孔/ ei轴=最小极限尺寸-基本尺寸 ES孔/ es轴 EI 孔/ ei轴 ei 0.008 (5) Size tolerance The allowable range for size variation. 尺寸公差 允许实际尺寸的变动量。 Φ49.992 es 0.005 Size tolerance=|Maximum limit size–Minimum limit size| |最大极限尺寸-最小极限尺寸| =| Upper deviation –Lower deviation | |上偏差 -下偏差| Φ50 50.005 Φ50.005

Example1: A hole is known Example1: A hole is known. Calculate these sizes D, Dmax, Dmin, DL, DM, ES, EI, and TD Solution: D=50mm Dmax=50.025mm Dmin=50mm DL= Dmax =50.025mm DM = Dmin =50mm ES=+0.025mm EI=0 TD= Dmax -Dmin =ES- EI=0.025mm

(6) Size tolerance zone In the tolerance zone diagram, an area bounded by the two lines represents the upper and lower deviation. 尺寸公差带(简称公差带) 在公差带图中，由代表上、下偏差的两条直线所限定的一个区域 。 ES es Hole 孔公差带 + ― Basic size 基本尺寸 Zeor line 零 线 Shaft 轴公差带 Standards specify that the size and location of the tolerance zone are determined separately, by the standard tolerance and basic deviation. 公差带的“大小”由“标准公差”确定, 公差带的“位置” 由“基本偏差”来确定。

Basic Deviation It is the upper or lower deviation used to determine the relative position between the tolerance zone and zero line. Generally, the deviation nearer to the zero line is treated as the basic deviation.

Basic concept of limits and fits 极限与配合的基本概念

2.3 Terms of Fit 配合术语 (1)General concept of fitting and its types 配合的基本概念及其种类 Fitting is the relationship between the matched hole and shaft with the same basic size. 基本尺寸相同的、相互结合的孔与轴公差带 之间的关系称为配合。 请 点 击 相 应 部 分 显 示 其 内 容 1) Clearance Fit Fit with clearance (including minimum clearance zero). It is used where there is relative movement between the hole and shaft. 间隙配合 具有间隙(包括最小间隙等于零)的配合。用于轴、 孔有相对运动处。 2) Interference Fit Fit with interference (Including minimum interference zero). It is used where there is no relative movement between the hole and shaft. 过盈配合 具有过盈(包括最小过盈等于零)的配合。一般用于轴、孔无相对运动处。 3) Transition Fit Fit having clearance of interference. The tolerance zone of the hole overlaps that of the shaft. It is used where there is a high neutral requirement. 过渡配合 可能具有间隙或过盈的配合。孔的公差带与轴的公差带相互重叠，一般用于对中性要求较高处。

Clearance Fit 间隙配合

Clearance Fits

Transition Fit 过渡配合

Transition Fits

Interference Fit 过盈配合

Interference Fits

Fit Tolerance : allow change amount of the clearance or interference and can be calculated as Clearance fit: Tf = |Xmax - Xmin| Interference fit: Tf = |Ymin - Ymax| Transition Fit: Tf = |Xmax - Ymax|

2.4 Series of Standard Tolerance 标准公差系列 Any tolerance specified in the limit standards and system of fits in GB/T 1800 series .Standard tolerance is represented with the ‘symbol IT’. The grade code of the tolerance is represented with numbers and there are 20 grade codes in total: IT01，IT0，IT1、IT2，…，IT18. In turn，total limit deviation falls from IT01 to IT18. 标准公差是在GB/T 1800系列标准极限与配合制中规定的任一公差。标准公差用符号“IT”表示,数字表示公差等级,共有20个等级,IT01,IT0,IT1,IT2,…IT18。 尺寸公差大 017级用于精密量具； 312级用于配合尺寸； 1218级用于非配合尺寸 尺寸精度高 Example: The tolerance grade of the hole is IT7 and IT12 ,Φ16、Φ44、Φ104 the tolerance value is: 例如,公差级别为IT7和IT12时,Φ16、Φ44、Φ104的公差值分别为: IT7the tolerance value is IT7标准公差值为： 0.018mm 0.025mm 0.035mm IT12 the tolerance value is IT12标准公差值为： 0.18mm 0.25mm 0.35mm

2.5 Series of Basic Deviation 基本偏差系列 Basic deviation is the limit deviation that determines the tolerance zone‘s location relative to the zero line in the GB/T 1800 series’ standard limit and system of fits. 基本偏差是指在GB/T 1800系列标准极限与配合制中,确定公 差带相对于零线位置的那个极限偏差。孔、轴各有28个基本偏差： Hole 孔 + EI ES 基本尺寸 + ei es Shaft 轴 基本尺寸

2.6 Selecting the Limits and Fits 选择极限和配合

H (2) Reference system of fits 配合的基准制： + - 1) Hole-based system of fit 基孔制 ： A system formed by both the tolerance zone of the hole, with definite basic deviation, and that of the shaft, with different basic deviations. 基本偏差为一定的孔的公差带与不同基本偏差的轴的公差带形成各种配合的一种制度。 The hole of the hole-based system is a basic hole, represented with H, the lower deviation of EI is zero. 基孔制的孔称为基准孔,用代号H表示,基准孔的下偏差EI=0。 基准孔公差带 ES  0 + - H ah 表示间隙配合； 配合性质： j、jsn 表示过渡配合； pzc 表示过盈配合。 基本尺寸

h + - 2) Shaft-based system of fit 基轴制 ： A system formed by both the tolerance zone of the shaft with definite basic deviation, and that of the hole with different basic deviations. 基本偏差为 一定的轴的公差带与不同基本偏差的孔的公差带形成各种配合的一种制度。 The shaft of the shaft-based system is a basic shaft, represented with h, the upper deviation of which is zero. 基轴制的轴称为基准轴 , 用代号 h表示, 其上偏差 es = 0。 + - es=0 h 基准轴公差带 基本尺寸 AH 表示间隙配合； 配合性质： J、JSN 表示过渡配合； PZC 表示过盈配合。

(3) Principles of selecting a reference system 基准制的选择原则： 1) The hole-based system is preferred. 一般情况下优先选用基孔制 2) The shaft-based system is used in the following situations: 基轴制用于以下三种情况 ①The shaft is made of cold drawing bar stocks without machining; 用冷拉棒料作轴，不需要再加工； ②The shafts of the same size form different fits with different holes; 同一基本尺寸的轴与几个孔组成不同的配合； ③ The fit between the external ring of the rolling bearing and the bearing housing adopts shaft-based system, for rolling bearing is a standard part. 滚动轴承的外圈与轴承座的配合采用基轴制。 (4) Principles of selecting a reference system 优先、常用配合 The national standard indicated the general, common and preferred tolerance zones for shafts and holes. 国家标准规定了一般、常用和优 先选用的孔、轴公差带以及相应的常用优先选用的配合。 Preferred hole basis fits, ordinary fits (基孔制优先、常用配合) Preferred shaft basis fits, ordinary fits (基轴制优先、常用配合)

Hole-based system of fit 基孔制配合 Clearance 间隙配合 Transition 过渡配合 Interference 过盈配合 Basic hole 基准孔

Shaft-based system of fit 基轴制配合 Clearance 间隙配合 Transition 过渡配合 Interference 过盈配合 Basic shaft 基准轴

Hole-based system of fit 基孔制配合 套的内表面与轴采用基孔制的间隙配合 孔与套的外表面采用基孔制的过渡配合

Shaft-based system of fit 基轴制配合 滚动轴承外圈与轴承座的配合采用基轴制 同一根轴上有不同配合要求

Selecting Grade of Tolerance 选择公差等级 Basic principle for selecting the grade of tolerance is that choosing a low tolerance grade as much as possible in the context of meeting the design requirements. In the general machinery industry, the tolerance grade being applied is varied between IT5~ IT12.

Selecting Fit System 选择配合系统 The guidelines for the selection of clearance fits are as follows: The fits H7-d8, H8-d9, and H11-dll are loose running fits, and are used for plumber-block bearings und loose pulleys. The fits H6-e7, H7-e8 and H8-e8 are loose clearance fits and are used for properly lubrication bearings, requiring appreciable clearances. The finer grades are used for heavy-duty, high-speed bearings and large electric motors. The fits H6-J6, H7-f7 and H 8-f8 are normal running fits widely used for grease or oil lubricated bearings, having low temperature rise. They are used for shafts of gear boxes, small electric motors and pumps. The fits H6-g5, H7-g6 and H8-g7 are expensive from manufacturing considerations. They are used in precision equipment, pistons, slide valves and bearings of accurate link mechanisms.

The general guidelines for the selection of transition fits are as follows: The typical types of transition fits are H6-j5, H7-j6 and H8-j7. They are used in applications where slight interference is permissible. Some of their applications are spigot and recess of the rigid coupling and the composite gear blank, where steel rim is fitted on ordinary steel hub. The fits H8/j7, H7/js6, H7/j6, and J7/h6 are small clearances or negligible interference. The parts can be assembled or disassembled manually. They are used for the easily dismountable fits of hubs of gears, pulleys and bushings, retaining rings, and frequently removed bearing bushings. The fits H8/k7, H7/k6, K8/h7, and K7/h6 are small clearances or small interferences. The parts can be assembled or disassembled without great force using a rubber mallet. They are used for demountable fits of hubs of gears and pulleys, manual wheels, clutches, and brake disks. The fits H8/p7, H8/m7, H8/n7, H7/m6, H7/n6, M8/h6, N8/h7, and N7/h6 are negligible clearances or small interferences, and are mounting of fits using pressing and light force. They are used for fixed plugs, driven bushings, armatures of electric motors on shafts, gear rims, and flushed bolts.

The general guidelines for the selection of interference fits are as follows: The fit H7-p6 or H7-p7 results in interference, which is not excessive but sufficient to give non-ferrous parts a light press fit. Such parts can he dismantled easily as and when required, e.g., fitting a brass bush in the gearing tolerances. The fits H8/s7, H8/t7, H7/s6, H7/t6, S7/h6, and T7/h6 are the pressed fits with medium interference. Assembling parts with such fits should use hot pressing or cold pressing only with use of large forces. These fits are used for permanent coupling of gears with shafts and bearing bushings. The fits H8/u8, H8/u7, H8/x8, H7/u6, U8/h7, and U7/h6 are the pressed fits with big interferences. Assembling parts with such fits should use great forces under different temperatures of the parts. These fits are used for permanent couplings of gears with shafts, flanges. 

Principles of selecting a reference system 优先、常用配合 Preferred hole basis fits, ordinary fits (基孔制优先、常用配合) Datum hole (基准孔) Shaft （轴） a b c d e f g h js k m n p r s t u v x y z Clearance fits (间隙配合) Transition fits (过渡配合) Interference fits (过盈配合) H6 f5 g5 h5 js5 k5 m5 n5 p5 r5 s9 t9 H7 f6 g6 h6 js6 k6 m6 n6 p6 r6 s6 t6 u6 v6 x6 y6 z6 H8 e7 f7 h7 js7 k7 m7 n7 p7 r7 s7 t7 u7 d8 e8 f8 h8 H9 c9 d9 e9 f9 h9 H10 c10 d10 h10 H11 a11 b11 c11 d11 h11 H12 a12 h12 注: H6 、 H7 n5 p5 在基本尺寸小于或等于3mm时为过渡配合； H8 r7 在基本尺寸小于或等于100mm时为过渡配合； 粉色的配合为优先配合。

Principles of selecting a reference system 优先、常用配合 Preferred shaft basis fits, ordinary fits (基轴制优先、常用配合) Datum shaft (基 准 轴) Hole （孔） A B C D E F G H JS K M N P R S T U V X Y Z Clearance fits (间隙配合) Transition fits (过渡配合) Interference fits (过盈配合) h5 F6 G6 H6 JS6 K6 M6 N6 P6 R6 S6 T6 h6 F7 G7 H7 JS7 K7 M7 N7 P7 R7 S7 T7 U7 h7 E8 F8 H8 JS8 K8 M8 N8 h8 D8 h9 D9 E9 F9 H9 h10 D10 H10 h11 A11 B11 C11 D11 H11 h12 B12 H12 注： 粉色的配合为优先配合。

Marking limits and fits 极限与配合的标注方法 (1) Marking in assembly drawings 在装配图中的标注 Φ40 Hole basic deviation code I T code 孔的基本偏差代号 公差等级 Basic size 基本尺寸 Shaft basic deviation code I T code 轴的基本偏差代号 公差等级 or 或 Basic size Tolerance zone code of the hole Tolerance zone code of the shaft 基本尺寸 孔的公差带代号 轴的公差带代号 Φ40H8/f7

Marking limits and fits 极限与配合的标注方法 (2) Marking in the detail drawings 在零件图中的标注 Φ40f7 Φ40H8 1) Marking code 代号注法 ： (用于大批量生产) Basic size 基本尺寸 Tolerance zone code 公差带代号 2) Marking values 数值注法 ： (用于单件小批量生产) 0的位置上下对齐 Upper deviation 上偏差值 Lower deviation 下偏差值 Basic size 基本尺寸 Φ40 Φ40 - 0.025 - 0.050 + 0.039 3) Comprehensive marking 综合注法： (用于产量不定) - 0.025 - 0.050 Φ40H8 Φ40f7 + 0.039 Upper deviation 上偏差值 Lower deviation 下偏差值 Basic size 基本尺寸 Tolerance zone code 公差带代号

Exercises 练 习 题 1. Point out the reference system of fits and types of fitting, and marking tolerance on a detail drawing. 指出所采用的基准制和配合种类,并在零件图中标注公差尺寸。 (用于产量不定) 2. Find out the incorrectly mark and correct it in the brackets. 找出公差配合标注中的错误, 并将正确的注法写在括号内。 3. The deviation of hole and shaft is: HoleФ 50 ShaftФ 50 （1） Representation of fits （2） Reference system of fits and types. 已知孔和轴的上下偏差为Ф 50 、 Ф 50 （1）画出孔和轴的公差带图； （2）说明基准制及配合种类。 ＋ 0.025 - 0.025 - 0.050 4. Graphical representation of fits, and complete the table for holes and shafts sizes, basic size is 15 and 55. 画出孔和轴的公差带图,并将基本尺寸为15mm 、55mm的孔和轴 的公差数值填入表中。 请点击题目显示其内容

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1. Point out the reference system of fits and types of fitting, and marking tolerance on a detail drawing. 指出所采用的基准制和配合种类,并在零件图中标注公差尺寸。 (用于产量不定) (1) Reference system of fits基准制： Hole-based system 据基孔制优先的原 则, 应属于基孔制； – 0.021 Φ30h7 (2) Types of fitting 配合种类： Clearance fit 因孔公差带 H 的下偏差为0 而轴公差带 h 的上偏差为0， 公差带无重叠, 即最小间隙 为0, 故应属于间隙配合。 Φ30 +0.033 Φ30H8 请点击解答显示其内容

-0 2. Find out the incorrectly mark and correct it in the brackets. +5 找出公差配合标注中的错误, 并将正确的注法写在括号内。 +5 -0 +43 +0.046 Φ10 Φ18 Φ75 Φ40 h8 g7 Φ30 H7 M7 Φ20 h6 (1) (2) (3) (4) (5) (6) Φ20 H6 h7 +0.005 Φ10 Φ30 H7 m7 +0.043 Φ18 Φ40 H8 g7 +0.046 Φ75 请点击解答显示其内容

3 . The deviation of hole and shaft is 已知孔和轴的上、下偏差为： Hole孔：Ф 50 Shaft轴：Ф 50 （1）Graphical representation of fits画出孔和轴的公差带图； （2）Reference system of fits and types: ______________ ,_________ 。 填空：孔与轴的基准制是: _____________ 制,________配合。 ＋ 0.025 - 0.025 - 0.050 Hole-basis system Clearance fit 基 孔 间 隙 Hole Shaft Ф 50 请点击解答显示其内容

4. Graphical representation of fits, and complete the table for holes and shafts sizes, basic size is Ф15mm and Ф55mm. 画出孔和轴的公差带图,并将基本尺寸为Ф15mm、Ф55mm 的孔和轴的公差数值填入表中。 FIT 配合 H 7- g 6 Ф + - H7 hole 孔 Basic size 基本尺寸 g 6 shaft轴  Clearance (间隙配合) Basic size 基本尺寸 Max.size Min.size最大尺寸 最小尺寸 ES EI Max.size Min.size最大尺寸 最小尺寸 es ei Hole 孔 Shaft 轴 + – 10 0.015 0 10.015 10.000 10 0.005 0.014 9.995 9.986 15 0.018 15.018 15.000 15 0.006 0.017 14.994 14.983 55 0.030 55.030 55.000 55 0.010 0.029 54.990 54.971