Important Definitions
31. Roughness width cut off : The distance used to find the arithmetical average deviation is called the roughness width cut off.
32.Waviness : It may be defined as the surface irregularities in the form of waves having larger wavelength.
33. Waviness height : It is the distance from the peak of the wave to its valley. It is measured in millimeters.
34. Waviness width : It is the spacing between the successive waves. It is measured in millimeters.
35. Lay : Lay is the primary direction of the surface pattern prepared by machine tool marks.
36. Flaws : They occur at random places on a machine component. These are cracks & scratches.
37. Ideal surface : It is a hypothetical perfect surface without any micro irregularity.
38. Actual surface : It is defined as surface of a part which actually is received after machining surface.
39. Nominal surface : A nominal surface is theoretical, geometrically perfect surface which is not to exist in the general practice.
40. Actual Profile : It is the actual surface obtained by a manufacturing process.
41. Datum Profile : The profiles which passes through the lowest points of actual profile is called Datum profile.
42. Mean Profile : The profiles which passes through the actual profile in such a way that the filled up areas between mean profile & actual profile is equal to the areas of voids between mean profile & actual profile within sampling length.
43. What is reference profile?
Ans 43: The profile which passes through the highest points of actual profile is called reference profile.
44. What do you mean by peak to valley height?
Ans 44: It is the distance between reference profile & datum profile.
45. Define mean roughness index.
Ans45: It is the arithmetic mean of absolute values of heights of peaks or depth of valleys.
46. Define surface roughness number.
Ans 46: It is the average departure of machined surface over a sampling length which is generally taken as 800 microns.
47. Draw the basic symbols of surface roughness.48. Define coupling.
Ans 48: It may be defined as the joining of two or more pieces of shafts in – order to obtain large length.
49. Where is Oldham’s Coupling best suited?
Ans 49: It is best suited to connect the shafts whose axes are parallel, but not in alignment.
50. Which material is used for Oldham’s Coupling?
Ans 50: Shafts – Mild Steel
Flanges & Disc – Cast Iron
Keys – Mild Steel
51. Draw roughness symbols with values & grade numbers.
