Page 275 - Aeronautical Engineer Data Book
P. 275
Basic mechanical design 221
Straightness
Axis is within a cylindrical
zone of diameter 0.1mm
0.1
Squareness
A
Datum Surface
0.1 A
Axis of hole to be within a cylindrical zone of diameter
0.1mm at 90° to the datum surface A
Parallelism
Datum line
A
0.1 B
B
Axis is within a cylindrical zone of diameter 0.1mm
parallel to the datum line A
Fig. 12.6 Straightness, parallelism and squareness
• Straightness: A hole or shaft can be straight
without being perpendicular to the surface
of the material.
• Parallelism: This is particularly relevant to
holes and is important when there is a
mating hole-to-shaft fit.
