00 Index and foreword
SEN00892-04
PC1250-8
9
Explanation of terms for maintenance standard
1
The maintenance standard chapter explains the criteria for replacing or reusing products and parts in the
machine maintenance work. The following terms are used to explain the criteria.
1.
Standard size and tolerance
q
To be accurate, the finishing size of parts
is a little different from one to another.
q
To specify a finishing size of a part, a tem-
porary standard size is set and an allow-
able difference from that size is indicated.
q
The above size set temporarily is called
the “standard size” and the range of differ-
ence from the standard size is called the
“tolerance”.
q
The tolerance with the symbols of + or – is
indicated on the right side of the standard
size.
a
The tolerance may be indicated in the text
and a table as [standard size (upper limit
of tolerance/lower limit of tolerance)].
Example) 120 (–0.022/–0.126)
q
Usually, the size of a hole and the size of
the shaft to be fitted to that hole are indi-
cated by the same standard size and dif-
ferent tolerances of the hole and shaft.
The tightness of fit is decided by the toler-
ance.
q
Indication of size of rotating shaft and hole
and relationship drawing of them
Example:
Standard size
Tolerance
120
–0.022
–0.126
Example:
Standard size
Tolerance
Shaft
Hole
60
–0.030
–0.076
+0.046
+
0
