surface finish

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For surface finish and plating of metals


At the end of this presentation, the students should be able to : Identify given surface texture symbols and explain their meanings

Select the type of surface texture, given charts relating surface textures to applications, and attainable surface textures to manufacturing processes. Indicate on engineering drawings, surface textures as well as machining processes using standard ISO symbols.

Main Menu1. Introduction

2. Roughness grade numbers

3. Symbols Used for Indication of Surface Texture

4. Indication on Drawings 5. When to Apply Surface Texture Symbols

1. Introduction Two main reasons for surface finish control are: to reduce friction to reduce wear

1. Introduction Factors to be considered in selecting surface finish: (i) function of the parts (ii) size (iii) type of loading (e.g. fatigue) (iv) speed (v) operating conditions (e.g. temperature) (vi) physical characteristics of materials in contact (vii) type and amount of lubricant.

2. Roughness grade numbers(Boundy Page 46)

Roughness Value (Ra)m 50 25 12.5 6.3 3.2 1.6 0.8 0.4 0.2 0.1 in 2000 1000 500 250 125 63 32 16 8 4

Roughness Grade NumberN12 N11 N10 N9 N8 N7 N6 N5 N4 N3

micrometre = 10-6m = m = micron = 40 inch

3. Symbols Used for Indication of Surface Texture (Table 1)S/No 1 Symbol MeaningBasic symbol. Needs to be accompanied by comments or Specifications e.g. to be machined if necessary.Removal of material is required



Removal of material is not permittedProduction method to be specified by indicating on the Horizontal line extending out. Surface treatment or coatings are also included here.



Same surface texture is required on all surfaces of the part

S/No S/No 6


MeaningWhen one value a is indicated, it represents the maximum Roughness allowed. a may be in roughness value or Roughness grade number.


When two values a1 and a2 are indicated, a1 = maximum roughness a2 = minimum roughness


c represents the sampling length in mm



Lay Symbols (Boundy, Table 1.21, Page 50)

Lay Symbols (Boundy, Table 1.21, Page 50)

Lay Symbols (Boundy, Table 1.21, Page 50)



4. Indication on Drawingbottomright side symbolinscriptions outside

4. Indication on DrawingExtension line Dimension line

Leader line Surface

4. Indication on Drawingmajority

4. Indication on Drawing

4. Indication on Drawing

Worked Example Worked ExampleA D B C roughness grade numbers is to be machined if necessary


Worked Example Worked Example Solution

A D B CN5 N4 N7




to be machined if necessary