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FOREWORD
EXPLANATION OF TERMS FOR MAINTENANCE STANDARD
The maintenance standard values necessary for judgment of products and parts are described by the following terms.
1.
Standard size and tolerance
•
To be accurate, the finishing size of parts is a little differ-
ent from one to another.
•
To specify a finishing size of a part, a temporary stan-
dard size is set and an allowable difference from that size
is indicated.
•
The above size set temporarily is called the "standard
size" and the range of difference from the standard size
is called the "tolerance."
•
The tolerance with the symbols of + or – is indicated on
the right side of the standard size.
Example:
Standard size
120
★ The tolerance may be indicated in the text and a table as
[standard size (upper limit of tolerance/lower limit of toler-
ance)].
Example: 120 (–0.022/–0.126)
●
Usually, the size of a hole and the size of the shaft to be fitted
to that hole are indicated by the same standard size and
different tolerances of the hole and shaft. The tightness of fit
is decided by the tolerance.
●
Indication of size of rotating shaft and hole and relationship drawing of them
Standard size
60
2.
Standard clearance and standard value
•
The clearance made when new parts are assembled is called the "standard clearance," which is indicated by the range
from the minimum clearance to the maximum clearance.
•
When some parts are repaired, the clearance is generally adjusted to the standard clearance.
•
A value of performance and function of new products or equivalent is called the "standard value," which is indicated
by a range or a target value.
•
When some parts are repaired, the value of performance/function is set to the standard value.
3.
Standard interference
•
When the size of a hole is smaller than the size of a shaft because of the standard size and tolerance, the difference
between these sizes is called the "interference."
•
The range (A – B) from the difference (A) between the minimum size of the shaft and the maximum size of the hole
to the difference (B) between the maximum size of the shaft and the minimum size of the hole is the "standard inter-
ference."
00-8
b
EXPLANATION OF TERMS FOR MAINTENANCE STANDARD
Tolerance
-0.022
-0.126
Tolerance
Shaft
Hole
-0.030
+0.046
-0.076
0
00
WB156PS-5
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