Interchangeability Measurements and Techniques - Calculation of Deviations and Tolerances, Drawing of Tolerance Charts, Selection of Fits and Tolerance Classes

1.尺寸

（1）公称尺寸（D,d）

（2）Extracts the local dimensions of components（Da,da）,Measured after processing

（3）极限尺寸（upper limit size,Lower limit size）

2.偏差：The allowable deviation from the nominal size

偏差=a certain size-公称尺寸

Limit deviation can be divided into upper deviation（ES,es）and lower deviation（EI,ei）

上偏差：upper limit size-公称尺寸

ES=Dmax-D

es=dmax-d

下偏差：Lower limit size-公称尺寸

EI=Dmin-D

ei=dmin-d

实际偏差：local size-公称尺寸

Ea=Da-D

ea=da-d

3.公差：Allowable size variation(upper limit deviation-lower limit deviation)

 hole tolerance

Tolerance of the shaft

4.Labeling of limit deviations

练习：

 First find the limit size of the shaft

The lower limit size of the shaft：

The upper limit size of the shaft：

因此第一个·and the last part failed

5.Tolerance zone diagram

 Note that the unit defaults to millimeters,The figures are marked in mm,Then the tolerance unit becomes microns

例题：

 6 配合

定义：The mutual positional relationship of the tolerance zone is used to reflect the relationship between the hole shafts with the same nominal size or the hole shafts combined with each other

 6.1 Clearance and interference

间隙X：孔的尺寸-轴的尺寸>=0

最大间隙：

最小间隙：

average clearance：

过盈Y:孔的尺寸-轴的尺寸<=0

Maximum interference:

Minimum interference：

 Average interference：

 6.2Match category

间隙配合

The tolerance zone of the hole is above the shaft

 过盈配合

The tolerance zone of the hole is below the shaft

 过渡配合

 6.3配合公差：The amount of variation in clearance or interference allowed

determines the quality of fit

6.4 配合制（Benchmark system）

基孔制配合：Tolerance zone location for fixing holes,Change the tolerance zone position of the axis,The lower deviation of the hole is 0

基轴制配合：The position of the tolerance zone of the fixed axis,Variation of the tolerance zone position of the hole,The upper deviation of the axis is 0

These are two parallel and equivalent mating relationships

7.Standard tolerance and basic deviation

7.1标准公差

 The determinant of the size of the standard tolerance value：Tolerance classes and nominal dimensions

 Commonly used hole and shaft fit,精度等级为IT5-IT12

7.2 标准偏差

 （1）The tolerance zone is above the zero line,The basic deviation is the lower deviation

（2）The tolerance zone is below the zero line,The basic deviation is the upper deviation

基本偏差代号

 （1）For base hole system,A-Hfor the upper deviation,J-ZCfor the lower deviation

（2）For the base axis system,A-Hfor the lower deviation,J-ZCfor the upper deviation

（3）基孔制：H,基轴制：h

（4）除了JS,js,K,k,M,NIn principle, the outer basic deviation has nothing to do with the standard tolerance,The basic deviation is to determine the position of the tolerance zone·的唯一参数

Note that holes are harder to machine than shafts,The accuracy class of the hole is one level lower than that of the shaft

8.Matching annotations

As shown in base hole system,The tolerance code of the hole is H,Tolerance class if selected as IT7,Then the tolerance level of the shaft should be one level higher than that of the hole,选择IT6, If a clearance fit is selected,The preferred fit tolerance classes in the table below can be selectedH7/g6

接下来,Look up the table according to the diameter and tolerance level to get the upper and lower limit deviation.

Tolerance class of the holeIT7,Tolerance class of the shaftIT6,

 Sixteen o'clock in diameter,Tolerance class of the holeIT7的公差为18μm,Because of the base hole system,The lower deviation of the hole is 0,因此,The upper deviation of the hole is +0.018.Tolerance class of the shaftIT6的公差为11μm.采用间隙配合,The shaft is below the tolerance zone,The basic deviation of the axis is the upper deviation.此时,We need to determine the base deviation of the axis（上偏差）.Check the table below（A table of basic deviations for the axis）知道,The deviation code is g时,The upper deviation is es=-0.006mm,由Td=es-ei=0.011,Get the deviationei=es-Td=-0.006-0.011=-0.017

9.Matching selection

（1）公差等级

原则：while meeting the usage requirements,Try to choose a grade with low precision

选用原则：

当D<=500mm,IT<=8,The hole axis difference is one level （Such as holes are6,7,8,轴就是5,6,7）

当D>500或IT>7,It's peer cooperation（Such as holes and shafts5,6,7）

（2）配合制（基孔制？基轴制？）

【1】The base hole system is preferred（Drills and reamers）

【2】In special cases, the base axis system is used（driveway or grinding wheel）

比如IT-IT1The cold-drawn steel directly makes the shaft,or diameter<1mm轴,A shaft is mated with the porous and the mating properties are different

【3】Compatible with the standard room,It is based on standard parts,For example, with bearings,Matching with the inner ring of the bearing is the base hole system,Matching with the outer ring of the bearing is the basic shaft system

【4】Mates are allowed to be formed with either bore shaft tolerance

（3）Match categories and types

【1】The mating surfaces have relative motion,Select a clearance fit

【2】The transmitted torque is the interference fit

【3】Can be disassembled multiple times,Select a clearance fit or transition fit

【4】Choice of tolerance zone

specific selection method：

计算法：Such as the clearance fit of sliding bearings

试验法：Important key fit,成本高

类比法：Production verified,similar institutions

（4）Dimensional tolerance not noted

Also called general tolerance,marked in the technical requirements

例如下图

 When designing, select according to the above table

例题：已知,要求X=+20~+90μm,If the base hole system is used,Determines the hole for this mate,Shaft tolerance zone and fit code,Draw its dimensional tolerance zone diagram

分析：Known base hole system,Therefore, the tolerance code of the hole is H,可得

According to the gap+20~+90μm,Get the fit tolerance

μm

Check the table above,in diameter40mm时,IT5=11μm,IT6=16μm,IT7=25μm,IT8=39μm,其中

IT5+IT6=11+16=27μm,IT6+IT7=41μm,IT7+IT8=64μm,All meet fit tolerances·的条件,According to the principle of economy,under the conditions of use,Choose a lower precision,And the hole is more difficult to machine,The accuracy class of the hole should be one class lower than the shaft,So the hole is IT8,轴为IT7,即

Next select the basic deviation code of the axis

Due to the use of base hole system,则EI=0,ES=39μm（IT8The time deviation is 39）,Next determine the basic deviation of the axises

由上图可知,Because it is a clearance fit,The basic deviation of the shaft is the upper deviationes

 (Because the tolerance class of the shaft isIT7,公差为25)

解得-26<=es<=-20

Next, check the basic deviation table of the shaft,可知es=-25,The tolerance code is f,因此

 Finally, draw the tolerance zone diagram

The upper deviation of the axis is es=-25μm,公差等级为IT7,查表知

Td=es-ei=25μm,因此ei=es-25=-25-25=-50μm

Because of the base hole system,So the lower deviation of the holeEI=0,Because the hole's tolerance class is IT8,因此TD=ES-EI=39μm,则,ES=39μm

所以：

Xmax=ES-ei=39-（-50）=89

Xmin=EI-es=0-（-25）=25