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For surface finish and plating of metals

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Page 1: Surface Finish
Page 2: Surface Finish

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.

At the end of this presentation, the students should be able to :

Page 3: Surface Finish

1. Introduction

3. Symbols Used for Indicationof Surface Texture

4. Indication on Drawings

5. When to Apply Surface Texture Symbols

2. Roughness grade numbers

Main Menu

Page 4: Surface Finish

1. Introduction

• Two main reasons for surface finish control are:

• to reduce friction

• to reduce wear

Page 5: Surface Finish

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.

Page 6: Surface Finish

Roughness Roughness Value (Ra) Grade Numberm in

50 2000 N12

25 1000 N11

12.5 500 N10

6.3 250 N9

3.2 125 N8

1.6 63 N7

0.8 32 N6

0.4 16 N5

0.2 8 N4

0.1 4 N3

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

2. Roughness grade numbers

(Boundy Page 46)

Page 7: Surface Finish

3. Symbols Used for Indication of Surface Texture (Table 1)

S/No Symbol MeaningS/No

1

2

3

4

5

Basic symbol. Needs to be accompanied by comments orSpecifications e.g. ‘to be machined if necessary‘.

Production method to be specified by indicating on the Horizontal line extending out. Surface treatment or coatings are also included here.

Removal of material is required

Removal of material is not permitted

Same surface texture is required on all surfaces of the part

Page 8: Surface Finish

S/No Symbol MeaningS/No

6

7

8

9

10

When 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

Specification of surface treatment/coating

a1 = roughness after coating

a2 = “ before “

a1 = is specified only if necessary

Direction of lay specified. Refer to Boundy, Table 1.21, Page 50.

Page 9: Surface Finish

Lay Symbols (Boundy, Table 1.21, Page 50)

• Parallel Circular

Page 10: Surface Finish

Lay Symbols (Boundy, Table 1.21, Page 50)

• Perpendicular Multidirectional

Page 11: Surface Finish

Lay Symbols (Boundy, Table 1.21, Page 50)

• Cross Radial

Page 12: Surface Finish

turned2.5

5

Page 13: Surface Finish
Page 14: Surface Finish

4. Indication on Drawing

• The symbol together with the inscriptions should be so orientated so that they can be easily read from the bottom or right side of the drawing,(ISO 129).

• However, if it is not practicable, the symbol may be drawn in any position, but only if it does not carry any indications of special surface texture characteristics. Nevertheless, the inscriptions of the symbol must be in accordance with ISO 129.

• As a general rule, the symbol or arrow line shall be applied to the surface or its extension line from outside the material.

Page 15: Surface Finish

4. Indication on Drawing

• Application of the surface texture symbol (Boundy, Fig.1.73, Page 46)

Leader line

Dimension line

Extension line

Surface

Page 16: Surface Finish

4. Indication on Drawing

• (c) When the same surface is required on the majority of surfaces

• Fig.2a Fig.2b

Page 17: Surface Finish

4. Indication on Drawing

• (d) Simplified indication

• Fig.3

0.80.8

0.8

Page 18: Surface Finish

4. Indication on Drawing

• (e) The symbol is used only once for a given surface and, if possible, on the view which carries the dimensions defining the size or position of the surface.

• Fig.4

Page 19: Surface Finish

5. When to Apply Surface Texture Symbols

• 5.1 Only if the application requires adequate specification of the surface quality, e.g. sliding fits, and only on those surfaces which require it.

• 5.2 The specification of surface texture is unnecessary whenever the ordinary manufacturing processes would normally give acceptable surface finish.

Page 20: Surface Finish

Application of surface texture symbol

(Boundy, Table 1.18, Page 47)

turned

Page 21: Surface Finish

Application of surface texture symbol

(Boundy, Table 1.18, Page 47)

Page 22: Surface Finish

Application of surface texture symbol

(Boundy, Table 1.18, Page 47)

milled

milled

Page 23: Surface Finish

Standard roughness values

(Boundy, Table 1.19, Page 48)

Page 24: Surface Finish

Standard roughness values

(Boundy, Table 1.19, Page 48)

Page 25: Surface Finish

Standard roughness values

(Boundy, Table 1.19, Page 48)

Page 26: Surface Finish

Worked Example

Indicate on Fig.5 the following surface texture requirements using roughness grade numbers:

(i) No material is to be removed from surface A,

(ii) Surface B is to be ground to a roughness value of 1.6 m,

(iii) Surface C is to be lapped to roughness value between 0.2 and 0.4 m. The direction of lapping is to be perpendicular to the plane of Fig.5.

(iv) Surface D is to be machined if necessary.

Fig.5

A

B

C

D

Worked Example

Page 27: Surface Finish

Worked Example

Fig.5

A

BC

D

ground

N7

= to be machined if necessary

Worked Example

Solution

lapped

N4N5