surface texture
TRANSCRIPT
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 :
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
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.
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)
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
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.
Lay Symbols (Boundy, Table 1.21, Page 50)
• Parallel Circular
Lay Symbols (Boundy, Table 1.21, Page 50)
• Perpendicular Multidirectional
Lay Symbols (Boundy, Table 1.21, Page 50)
• Cross Radial
turned2.5
5
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.
4. Indication on Drawing
• Application of the surface texture symbol (Boundy, Fig.1.73, Page 46)
Leader line
Dimension line
Extension line
Surface
4. Indication on Drawing
• (c) When the same surface is required on the majority of surfaces
• Fig.2a Fig.2b
4. Indication on Drawing
• (d) Simplified indication
• Fig.3
0.80.8
0.8
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
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.
Application of surface texture symbol
(Boundy, Table 1.18, Page 47)
turned
Application of surface texture symbol
(Boundy, Table 1.18, Page 47)
Application of surface texture symbol
(Boundy, Table 1.18, Page 47)
milled
milled
Standard roughness values
(Boundy, Table 1.19, Page 48)
Standard roughness values
(Boundy, Table 1.19, Page 48)
Standard roughness values
(Boundy, Table 1.19, Page 48)
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
Worked Example
Fig.5
A
BC
D
ground
N7
= to be machined if necessary
Worked Example
Solution
lapped
N4N5