PC128US-8
00-17
00 Index and foreword
Explanation of terms for maintenance standard
2.
Standard clearance and standard value
q
The clearance made when new parts are
assembled is called the “standard clear-
ance“, which is indicated by the range
from the minimum clearance to the maxi-
mum clearance.
q
When some parts are repaired, the clear-
ance is generally adjusted to the standard
clearance.
q
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.
q
When some parts are repaired, the value
of performance/function is set to the stan-
dard value.
3.
Standard interference
q
When the diameter of a hole of a part
shown in the given standard size and tol-
erance table is smaller than that of the
mating shaft, the difference between those
diameters is called the “interference”.
q
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 interference”.
q
After repairing or replacing some parts,
measure the size of their hole and shaft
and check that the interference is in the
standard range.
4.
Repair limit and allowable value or allow-
able dimension
q
The size of a part changes because of
wear and deformation while it is used. The
limit of changed size is called the “repair
limit”.
q
If a part is worn to the repair limit, it must
be replaced or repaired.
q
The performance and function of a prod-
uct lowers while it is used. A value which
the product can be used without causing a
problem is called the “allowable value” or
“allowable dimension”.
q
If a product is worn to the allowable value,
it must be checked or repaired. Since the
permissible value is estimated from vari-
ous tests or experiences in most cases,
however, it must be judged after consider-
ing the operating condition and customer's
requirement.
5.
Clearance limit
q
Parts can be used until the clearance
between them is increased to a certain
limit. The limit at which those parts cannot
be used is called the “clearance limit”.
q
If the clearance between the parts
exceeds the clearance limit, they must be
replaced or repaired.
6.
Interference limit
q
The allowable maximum interference
between the hole of a part and the shaft of
another part to be assembled is called the
“interference limit”.
q
The interference limit shows the repair
limit of the part of smaller tolerance.
q
If the interference between the parts
exceeds the interference limit, they must
be replaced or repaired.
