Introduction to Basic Manufacturing Processes and ... - always yours

Inspection and Quality Control 471
fit where a small amount of either clearance or interference is permissible. Transition fit is
of two kinds namely push fit and light keying fits. That is, sometimes shaft is slightly larger
than the hole and sometimes slightly smaller than the hole. Spigot in mating holes, coupling
rings and recesses are the examples of transition fit.
26.5 HOLE BASIS SYSTEM
When hole is kept as constant member and different fits are obtained by varying the
shafts sizes in a particular fit shown in Fig. 26.6, then the limit system is known as hole basis
system.
26.6 SHAFT BASIS SYSTEM
When shaft is kept as constant member and different fits are obtained by varying the
hole sizes as shown in Fig. 26.6, then the limit system is termed as shaft basis system of
making sub-assembly or assembly.
Hole
Shaft
Shaft
Shaft
Shaft
Shaft
Hole
Zero line
Basic size
Hole
Shaft
Hole Shaft
Hole
Hole
Shaft
Hole
26.7 SURFACE FINISH
Fig. 26.6 Hole basis system and shaft bases system
Good surface finish on part has become an essential requirement of a product quality
and for its better life. By imparting a surface finishing process on the part, its dimension does
not change functionally and significantly. Either a very negligible amount of material is
removed or certain material is added to the surface of the job. Surface finishing processes
should not be misunderstood as metal removing processes in any case as they are primarily
intended to provide a good surface finish or decorative or protective coating on to the metal
surface for its better life and excellent appearance. Surface cleaning process is also accepted
as a surface finishing process. Some of the such surface finishing processes are lapping,
honing, super finishing, belt grinding, polishing, sanding, tumbling, organic finishes, deburring,
electroplating, buffing, metal spraying, painting, inorganic coating, anodizing, parkerizing,
galvanizing, plastic coating, metallic coating and anodizing. The characteristics of good finish
or roughness of surfaces can be understood by following components, which are described as
under.
26.7.1 Roughness (Primary texture)
It refers to relatively finely spaced surface irregularities of small wavelength on the part
which results from the inherent action of the manufacturing process. It may involve transverse
feed marks and the irregularities on the machined surface.