Dimensions, Surfaces, and Their Measurements

the predominant direction or pattern of the texture of a surface is called

lay

the surface texture Ra is a measure of:

roughness

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 waviness deviations

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; it varies depending on direction; it does not indicate lay; its value depends on the roughness width cutoff used to measure the average

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 and the changes in it

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

the average value of the vertical deviations from the nominal surface over a specified surface length

what are common methods for assessing surface roughness

1. comparison of the specimen surface with standard test blocks having known surface roughness values 2. stylus-type electronic instruments which measure average roughness

what is accuracy in measurement

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

what is precision in measurement

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

what is meant by the term graduated measuring device

a graduated measuring device has markings called graduations on a linear or angular scale to measure an object's feature of interest

what are some of the reasons why surfaces are important

aesthetics, safety, friction and wear, effect of surface on mechanical and physical properties, mating of components in assembly, and electrical contacts

what is the difference between a bilateral tolerance and a unilateral tolerance

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

name some manufacturing processes that produce poor surface finishes

casting, hot rolling, sawing, and thermal cutting

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

cracks, craters, variations in hardness near the surface, metallurgical changes resulting from heat, residual stresses, inter-granular attack

the surface finish of casting would be expected to be numerically _______ a finished machined part (via turning or milling)

higher than

name some manufacturing processes that produce good surface finishes

honing, lapping, polishing, and superfinishing

define nominal surface

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

define surface texture

the random and repetitive deviations from the nominal surface, including roughness, waviness, lay, and flaws

what is a tolerance

the total amount by which a specified dimension is permitted to vary

a tolerance in which variance from the nominal dimension is permitted in only one direction is called:

unilateral