In the drawing of a part, not only the shape and size of the part must be clearly expressed, but also the necessary technical requirements for the material, processing, inspection, measurement, etc. of the part should be put forward. Use the specified code, number, text, etc. to indicate the technical indicators that the parts should reach during the manufacturing and inspection process. The main contents of these indicators include: surface roughness, dimensional tolerance, shape and position tolerance, material and heat treatment, etc. And this article will take you through the annotations on surface roughness.

Let’s get started right away!

The concept of surface roughness

The micro-geometric shape characteristic composed of peaks and valleys with small spacing on the surface of the part is called surface roughness. This is mainly due to the knife marks left by the tool on the surface of the part and the plastic deformation of the surface metal during cutting and splitting when the part is processed.
The surface roughness of parts is also a technical index for evaluating the surface quality of parts. It has an impact on the matching properties, working accuracy, wear resistance, corrosion resistance, sealing performance and appearance of parts.

The main evaluation parameters of surface roughness

1) Contour arithmetic mean deviation (Ra)

Within the sampling length, the arithmetic mean of the absolute value of the contour offset.

2) The maximum height of the profile (Rz)

Within the sampling length, the distance between the top line of the profile peak and the bottom line of the profile peak. Remarks: Ra parameter is preferred when using.

Marking requirements for surface roughness

1) Example of code labeling for surface roughness

When the surface roughness height parameters Ra, Rz, Ry are marked with numerical values in the code, except that the parameter code Ra can be omitted, the corresponding parameter code Rz or Ry must be marked before the parameter value.

2) The method of labeling the numbers and symbols in the surface roughness

The surface roughness code (symbol) should generally be marked on the visible contour line, dimension extension line or their extension, and the tip of the symbol must point from the outside of the material to the surface. In addition, the direction of numbers and symbols in the surface roughness code must be marked according to regulations.

Annotation example for surface roughness

On the same drawing, each surface is generally only marked with a code (symbol) once, and it should be as close as possible to the relevant dimension line. When the space is narrow or it is inconvenient to mark, the mark can be drawn out. When all surfaces of a part have the same surface roughness requirements, they can be uniformly marked on the upper right corner of the drawing. When most surfaces of the parts have the same surface roughness requirements, the most used code (symbol) can be used At the same time, note in the upper right corner of the pattern, and add the word “rest”. The height of the uniformly marked surface roughness code (symbol) and explanatory text should be 1.4 times that of the drawing mark.
For the continuous surface on the part, the surface of repeated elements (such as holes, teeth, grooves, etc.), and the same surface connected with discontinuities by thin solid lines, the surface roughness code (symbol) is only marked once.
When there are different surface roughness requirements on the same surface, the dividing line shall be drawn with a thin solid line, and the corresponding surface roughness code and size shall be indicated.
The working surface of the center hole, the working surface of the keyway, the chamfer, and the surface roughness code of the fillet can simplify the labeling.
When partial heat treatment or partial plating (coating) of parts is required, the range shall be drawn with thick stippling lines and the corresponding dimensions shall be marked, or the requirements may be written on the horizontal line of the long side of the surface roughness symbol.

Hope the above content can help you.