23-08-2013, 04:33 PM
Limits, Fits and tolerances
Limits, Fits .pdf (Size: 679.39 KB / Downloads: 124)
SYSTEM OF FITS AND TOLERANCES
The standard reference temperature is 20 C for industrial measurements
and, consequently, for dimensions defined by the system.
Due to the inevitable inaccuracy of manufacturing methods, a part
cannot be made precisely to a given dimension, the difference between
maximum and minimum limits of size is the tolerance.
When two parts are to be assembled, the relation resulting from the
difference between their sizes before assembly is called a fit.
•The upper deviation or the upper limit of size
shall be written in the upper position and the lower
deviation or the lower limit of size in the lower
position, irrespective of whether a hole or a shaft is
toleranced.
•The tolerance symbol for the
hole shall be placed before that
for the shaft or above it, the
symbols being preceded by the
basic size indicated once only.