It is also known as the height of unevenness. Roughness Width: The roughness width is the distance parallel to the nominal surface between successive peaks or ridges which constitute the predominant pattern of the roughness. It is measured in millimeters.
Roughness Width Cut Off: Roughness width cut off is the greatest spacing of respective surface irregularities to be included in the measurement of the average roughness height. It should always be greater than the roughness width in order to obtain the total roughness height rating. Lay: Lay represents the direction of the predominant surface pattern produced and it reflects the machining operation used to produce it.
Waviness: This refers to the irregularities which are outside the roughness width cut-off values. Waviness is the widely spaced component of the surface texture. This may be the result of workpiece or tool deflection during machining, vibrations, or tool run out. Waviness Width: Waviness height is the peak to valley distance of the surface profile, measured in millimeters.
The BIS has prescribed twelve grades of surface roughness. These grades of surface roughness. These grades of surface roughness are numbered as N1, N2, N3….. The standard prescribed grades of surface roughness may be chosen from the given Table-A corresponding to the required surface roughness values.
When the quality of surface finish is to be indicated by the roughness grade number in the surface finish symbol, the grade number is written in the same place of the roughness value the Figure-A. The BIS Bureau of Indian Standards prefers the sign of surface roughness either by grades or by values, from the point of the requirements of overall engineering industries.
It is suggested to indicate the surface roughness on drawing by symbols. The number triangles indicate the range of surface roughness.
Terminology explanation Surface texture This is a general term for factors such as the roughness, necessity of removal machining, crease direction, and waviness of the surface of machine parts and structural parts. Removal machining This refers to the removal of surface layers from parts by way of machining or similar methods. Crease direction This is the direction of clear creases that are formed during removal machining. This is a general term for factors such as the roughness, necessity of removal machining, crease direction, and waviness of the surface of machine parts and structural parts.
This refers to the removal of surface layers from parts by way of machining or similar methods. Example Shaped surface. Roughness Roughness includes the finest shortest wavelength irregularities of a surface. Roughness generally results from a particular production process or material condition. Waviness Waviness includes the more widely spaced longer wavelength deviations of a surface from its nominal shape. Waviness errors are intermediate in wavelength between roughness and form error.
Note, that distraction between waviness and form error is not always made in practice and it is not always clear how to make it.
Lay Lay refers to the predominant direction of the surface texture. Ordinarily, lay is determined by the particular production method and geometry used.
Surface roughness heights are generally measured in micro inches or micrometers. Terminology explanation This is a general term for factors such as the rou ghness, necessity of Surface texture removal machining, crease direction, and waviness of the surface of mach i ne parts and structural parts.
This refers to the removal of surface layers from parts by way of Removal machining mach i n i ng or similar methods. This is the direction of clear creases that are formed during removal Crease direction mach i n i ng. The descriptors shown below are used when pictorially representni g surface roughness. However, generaly speaking, the standard condti ions, which are shown in red,are omtted i ,and the indications shown in blue l only when necessary. Example Shaped surface The creases made by the edged tool during machining are pe rpe nd i cular to the surface captured in the diagram i n w hich the symbol i s wr i tten.
Example Shaped surface turned on a l athe ; seen from t he si de , c ylindri ca l l y ground surface The creases made by the edged tool during machining are at an angle and cross each oth er on the surface ca ptured in the diagram in whi ch the symbo l i s wr i tte n.
Ex ample Ho ning fin i shed surface The creases made by the edged tool during machining cross mult i p l e times or have no set direction. Example Lapped surface, su per - f i n i shed surface, face -mi l l ed or end-m i l led surface tha t has been cross fed The creases made by the edged tool during machining form mostly concentric circ l es i n re l ation to the center of the surface on wh i ch the s ymbo l i s wr i tten.
Machined Surfaces Interpretation of surface traces To be of any use to humans, surface traces are magnified moderately in the horizontal direction and significantly in the vertical direction in order to be presented on a computer screen or a piece of paper. This is a 40X magnification horizontally and a 10,X magnification vertically.
This differences leads to a very sharply undulating trace that easily deceives the uninitiated as to the actual shape of the surface. Figure 2: Interpretation of surface trace The vertical magnification of a surface trace is ordinarily much greater than the horizontal magnification. A trace that looks jagged and rough to the eye is really a distorted view of a nearly flat surface with moderate ripples across it. Figure 3 presents the actual surface texture plot taken by a surface roughness measuring instrument in a laboratory.
Figure 3: Roughness amplitude parameter for Interpretation of surface roughness plot There can be many ways, thro which the surface roughness plot can be interpreted. As per the data, worldwide more than conventions are available for interpreting above graph and presenting the results in the drawing! The most common and popular method amongst all is interpreting thro average roughness indication.
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