Dimensioning and Specifications for Assembly Drawings(装置图的标注)

Dimensioning( 尺寸标注)

In an assemblydrawing, only the following dimensions are marked: 


Characteristic and specification dimensions(特性与规格尺寸)

The dimensions that represent machine specifications or service behaviors are the foundation on which users choose the right products, such as travel distances, calibers and threads. For example, the dimension G1/4 of gas thread and diameter φ4mm of the oil entrance and exit in the gear pump shown in Fig. 9-11 is related to the volume of the incoming and outgoing oil, therefore this dimension is a characteristic and specification dimension.


External dimensions (外形尺寸)

The dimensions that represent the general length, width, and height are useful for packing, distribution and transportation. In Fig.9-11, for example, the total length is 150mm, total width is 80mm, and total height is 100mm.


Fitting dimensions(装配尺寸)

Fitting dimensions represent dimensions and related tolerances between parts or subassemblies that have the following characteristics:

1) The distance from the main axis to the mounting datum face, such as the center height of 45mm for the driving-shaft(part 10)inthe assembly drawing of the gear pump shown in Fig. 9-11.

2) The distance between the main parallel shafts, such as the center distance  mm of the driving-shaft(part 10)and driven-shaft(part 5)in Fig.9-11.

3) The fitting relationship that must be kept after mounting, such as the fitting dimension of driving-shaft(part 10), driven-shaft(part5),pump body(part 3)and pump cover(part 1)in the gear pump are allφ13H8/f7


1) 主要轴线到安装基准面的距离。如图9-11齿轮泵装配图中,主动轴(件10)的中心高45mm。

2) 主要平行轴之间的距离。如图9-11齿轮泵中主动轴(件10)与从动轴(件5)的中心距mm。

3) 装配后两零件之间必须保证的配合关系。如图9-11齿轮泵中主动轴(件10)、从动轴(件5)与泵体(件3)和泵盖(件1)的配合尺寸均为φ13H8/f7等。

Mounting dimensions(安装尺寸)

Mounting dimensions include those that are required to mount the machine or subassembly to its base or to another units. For example, the center distance 56mm of two holes and the dimension 2×φ11mm of the hole on the base of the pump body(part3)(Fig.9-11). 


Other important dimensions(其他尺寸)

Other important dimensions include dimensions of major parts and limit dimensions of moving parts, such as the radius R25mm of the distribution of the threaded holes used to mount screws on the pump body and pump cover.