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Explanation of terms for maintenance standard
The chapter of maintenance standard shows judgement criteria to determine the products to be replaced
q
or to be reused. The judgement criteria are described by using the following terms.
Standard dimension and tolerance
To be accurate, the finished dimension of a
q
part is slightly different from one to another.
The finished dimension of a part specifies the
q
allowable difference from the standard di-
mension which is set first.
The dimension set as the standard is called
q
the standard dimension and the range of dif-
ference from this standard dimension is
called the "tolerance".
An indication example of a standard dimen-
q
sion and tolerance is shown in the following
table.
(The standard dimension is entered on the
left side and the tolerance is entered with a
positive or negative symbol on the right side)
Example:
Standard dimension
120
a The tolerance may be indicated in the text
and a table as "standard dimension (upper
limit of tolerance/lower limit of tolerance)."
Example: 120(-0.022/-0.126)
Usually, the dimension of a hole and the di-
q
mension of a shaft to be inserted into the hole
are indicated by the same standard dimen-
sion and different tolerances of the hole and
shaft.
The tightness of fit is decided by the toler-
ance.
An indication example of a shaft and hole is
q
shown in the following table.
(The standard dimension is entered on the
left side and the tolerance of the shaft is en-
tered with a positive or negative symbol at
the center and that of the hole on the right
side)
Standard
dimension
60
Standard clearance and standard value
The clearance made when new parts are as-
q
sembled 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
q
generally adjusted to the standard clearance.
WA200-7
Tolerance
-0.022
-0.126
Tolerance
Shaft
Hole
-0.030
+0.046
-0.076
0
Explanation of terms for maintenance standard
The values indicating performance and function
q
of new products or equivalent are called the
"standard value", which is indicated by a range
or a target value.
When some parts are repaired, the value of per-
q
formance/function is set to the standard value.
Standard interference
When the diameter of a hole of a part shown in
q
the given standard dimension and tolerance ta-
ble is smaller than that of the shaft to be inserted,
the difference between those diameters is called
the "interference".
Subtract the maximum dimension of the hole
q
from the minimum dimension of the shaft and
call it (A). Subtract the minimum dimension of
the hole from the maximum dimension of the
shaft and call it (B). The range between (A) and
(B) is the "standard interference".
After repairing or replacing some parts, measure
q
the dimension of their hole and shaft and check
that the interference is in the standard range.
00 Index and foreword
(Rev. 2012/10)
00-23
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