Chapter 5

What is the difference between a bilateral tolerance and a unilateral tolerance?

A bilateral tolerance allows variation in both positive and negative directions from the normal dimension, whereas a unilateral tolerance allows the variation from the nominal dimension to be either positive or negative, but not both

What is meant by the term graduated measuring device?

A graduated measuring device has markings (called graduations) on a linear of angular scale to measure an objet's feature of interest (length).

What are the methods for assessing surface roughness?

Common methods for assessing surface roughness are 1. comparison of the specimen surface with standard text blocks having known surface roughness values 2. stylus-type electronic instruments which measure average roughness 3. optical techniques

What causes the various types of changes that occur in the altered layer just beneth the surface?

Energy input to the surface resulting from the manufacturing process used to generate the surface. The energy forms can be any several types, including mechanical, thermal, chemical, and electrical.

What is precision in measurement?

Precision in measurement is the degree to which random errors are minimized.

Name some manufacturing processes that product very good or excellent surface finishes

Processes that produced very good or excellent surfaces include honing, lapping, polishing, and superfinishing

Name some manufacturing processes that product very poor surface finishes

Processes that product poor surfaces include sand casting, hot rolling, sawing, and thermal cutting

Within the scope of surface texture, how is roughness distinguished from waviness?

Roughness consists of the finely-spaced deviations from the nominal surface, while waviness refers to the deviations of larger spacing. Roughness deviations lie within the waviness deviations.

Surface roughness is a measurable aspect of surface texture; what does surface roughness mean?

Surface roughness is defined as the average value of the vertical deviations from the nominal surface over a specified surface length.

Indicate some of the limitations of using surface roughness as a measure of surface texture.

Surface roughness provides only a single measure of surface texture. Among its limitations are: 1. it varies depending on direction 2. it does not indicate lay 3. its value depends on the roughness width cutoff used to measure the average

Define surface texture

Surface texture is the random repetitive deviations from the nominal surface, including roughness, waviness, lay, and flaws.

How is surface texture distinguished from surface integrity?

Surface texture refers only to the surface geometry; surface integrity includes not only surface but the subsurface layer beneath the surface and the changes in it.

Identify some of the changes and injuries that can occur at or immediately below the surface of a metal

The changes and injuries include residual stresses, surface hardening or softening, cracks, craters, heat affected zones, inclusions of foreign particles, and intergranular attack of chemicals

What is accuracy in measurement?

The degree to which the measured value agrees with the true value of the quantity of interest. It is the measurement that is absent of systematic errors.

Define nominal surface.

The nominal surface is the ideal part surface represented on an engineering drawing. It is assumed perfectly smooth, perfectly flat if referring to a planar surface, perfectly round if referring to a round surface, etc.

What are some of the reasons why surfaces are important?

The reasons why surfaces are important include aesthetics, safety, friction and wear, effect of surface on mechanical and physical properties, mating of components in assembly, and as electrical contacts

What is tolerance?

The total amount by which a specified dimension is permitted to vary.