Tutorial 6ge3o

Tutorial (1) 1. What is a tolerance?  It is the difference between the upper limit and the lower limit of a dimension. It is also the maximum permissible variation in a dimension.  A limited variation is allowed from the dimension and that allowable variation is called tolerance. 2. What is the difference between a bilateral tolerance and a unilateral tolerance? Bilateral Tolerance  It’s the variation permitted in both positive and negative directions from the nominal dimension.  Example,

+0.005∈¿ ¿ −0.005∈¿ 2.5∈¿ ¿ ¿

Unilateral Tolerance  It’s the variation from the specified dimension permitted in only one direction, either positive or negative.  Example,

+0.005∈¿ +0.002∈¿¿ 2.5∈¿¿ ¿

3.What is accuracy in measurement?  Accuracy is the degree to which the measured value agrees with the true value of the quantity of interest. 4.What is precision in measurement?  It’s the degree of repeatability in the measurement process. Good precision means that random errors in the measurement procedure are minimized. 5. What is meant by the term graduated measuring device?  It includes a set of marking (graduations) on a linear or angular scale to which the object’s feature of interest can be compared for measurement. 6.Define Nominal surface.  It represents the intended surface contour of the part, which is defined by lines in engineering drawing. 7. What are some of the reasons why surfaces are important? i. Aesthetic reasons

ii. Surface affect safety iii. Friction and wear depend on surface characteristics iv. Surfaces affect mechanical and physical properties v. Assembly of parts is affected by their surfaces vi. Smooth surfaces make better electrical s 8. Define surface texture.  Surface texture consists of the repetitive and/or random deviations from the nominal surface of an object; it is defined by four features: roughness, waviness, lay and flaws. 9.How is surface texture distinguished from surface integrity?  Surface texture consists of the repetitive and/or random deviations from the nominal surface of an object; it is defined by four features: roughness, waviness, lay and flaws.  Surface integrity is the study and control of this subsurface layer and any changes in it because of processing that may influence the performance of the finished part or product. 10.Within the scope of surface texture, how is roughness distinguished from waviness?  Roughness refers to the small, finely spaced deviations from the nominal surfaces.  Waviness is defined as the deviations of much larger spacing.  Cutoff length is used as a filter that separates the waviness in a measured surface from the roughness deviations, the cutoff length is a sampling distance along the surface. A sampling distance shorter than the waviness width will eliminate the vertical deviations associated with waviness and only include those associate with roughness.  The most common cutoff length in practice is 0.8mm (0.03 in). 11.What are the common methods of assessing surface roughness?  Sets of standard surface finish blocks are available, produced to specified roughness values.  To estimate the roughness of a given test specimen, the surface is compared with the standard both visually and by fingernail test.