Explanation Of Terms For Maintenance Standard - Komatsu PC88MR-10 Shop Manual

00 Index and foreword
Foreword, safety and general information

Explanation of terms for maintenance standard

The chapter of maintenance standard shows judgement criteria to determine the products to be replaced
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 part
is slightly different from one to another.
The finished dimension of a part specifies the
allowable difference from the standard
dimension which is set first.
The dimension set as the standard is called the
standard dimension and the range of difference
from this standard dimension is called the
"tolerance".
An indication example of a standard dimension
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
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
dimension of a shaft to be inserted into the hole
are indicated by the same standard dimension
and different tolerances of the hole and shaft.
The tightness of fit is decided by the tolerance.
An indication example of a shaft and hole is
shown in the following table.
(The standard dimension is entered on the left
side and the tolerance of the shaft is entered
with a positive or negative symbol at the center
and that of the hole on the right side)
Standard
dimension
-0.030
60
-0.076
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.
The values indicating performance and function
of new products or equivalent are called the
"standard value", which is indicated by a range
or a target value.
00-22
Tolerance
-0.022
-0.126
Tolerance
Shaft Hole
+0.046
0
(ALL-0330-006-A-01-A)
When some parts are repaired, the value of
performance/function is set to the standard
value.
Standard interference
When the diameter of a hole of a part shown in
the given standard dimension and tolerance
table 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
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
the dimension of their hole and shaft and check
that the interference is in the standard range.
Repair limit and allowable value or allowable
dimension
The dimensions of parts change because of the
wear or deformation while they are used. When
the dimension changes exceeding certain value,
(Rev. 2012/10)
PC88MR-10