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How do I establish / evaluate the life
of a thread gauge?
You can evaluate the life of thread gauges used by you, considering
the following factors, which affect the life of thread gauges.
- Identify wear parameters i.e. major diameter & pitch
diameter of Thread Plugs and Minor diameter & pitch
diameter for thread rings. Flank Angle and pitch can also
be considered. Most effective is the Pitch diameter.
- Measure / Calibrate the Pitch diameter periodically for
a batch of gauged components.
- Analyse the wear pattern of the pitch diameter on reaching
the complete specified wear limit as against the number
of gauged components.
- This analysis should help you to establish the life of
a thread gauge and work out a plan to improve the gauge
life.
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What are the factors contributing for
the normal life of thread gauges?
The factors which contribute towards life of thread gauges
are
- Material & Heat treatment of gauges
- Thread flank surface finish of gauges
- Material of gauging components
- Fitment of gauging
- Hardness of raw material
- Manufacturing process control of components
i.e. Tolerance system on components
- Lubrication while gauging & after gauging
- Cleanliness of cut threads on components
- Driving force of gauging
- Handling and preservation of gauges.
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How can I improve the life of a thread gauge?
You can improve the life of a thread gauge by taking the following
precautions Use a correct thread gauge i.e. of the correct class
of fit and tolerance disposition. Clean the component to be
gauged of metal chips, sharp edges before gauging.
Use suitable lubrication while gauging to avoid dry and hard
drive while gauging.
Manufacturing process control of component to give smooth gauging
i.e. To manufacture component with free fit and not close fit
to thread gauges.
The thread gauge should enter the threaded portion of the component
by using normal hand force. Avoid trying to force the gauge
in the component. Handle thread gauges with care. Thread plug
gauges are more prone to damage on the external diameter, if
not handled properly. Clean the gauge after use and apply oil
or a suitable anti-rust formulation. |
Is it possible to use thread gauges which are approaching or have exceeded the wear limits?
The use of thread gauges which are approaching or have exceeded
the wear limits is not recommended. This is illustrated by the
following example. Let us assume that you want to manufacture
bolts and nuts of the same size.
The pitch diameter of the thread plug gauge that you use to
check the nuts is at the wear limit. The nuts manufactured and
checked with this thread plug gauge will also be on the minimum
side or may be undersize.
The thread ring gauge used to check the bolts is worn out and
its pitch diameter has reached the wear limit. The bolts manufactured
and checked with this thread ring gauge will be at the maximum
limit or may be oversize.
When you try to mate the bolts and nuts which have been checked
with gauges at the wear limits, the probability of risk that
they may not mate easily or may not mate at all, is very high. |
Can the maximum metal condition of thread gauges serve the
purpose of obtaining maximum life of that gauge?
Yes, but only to a certain extent.
You use a thread gauge to check the threads of the components.
Let us assume that you manufacture nuts and bolts of the same
size.
You have the corresponding thread ring and thread plug gauges
at the maximum metal condition i.e. the effective diameter of
the thread plug gauge is at the maximum and the effective diameter
of the thread ring
gauge is at the minimum permissible level.
Since the thread plug gauge is at the maximum level, the nuts
checked by it will also be at the maximum level or in some cases
may be oversize. Since the thread ring gauge is at the minimum
level (remember :
maximum metal condition) the bolts checked by it will be at
the minimum level or in some cases may be undersize.
When you try to mate the nuts and bolts which have been checked
with thread gauges at the Maximum Metal Condition, the probability
of risk that the fitment being loose, is very high Thus you
see, that while you may obtain a longer life for the thread
gauge, you may not get the desired fitment between the mating
components with a high risk of reducing & minimizing the
working manufacturing tolerance of nuts and bolts. |
How do I work out the wear limits of a thread gauge?
The wear limit of a thread gauge is checked by using a wear
check gauge. The wear check gauge is used to ascertain that
the pitch diameter of the thread gauge has not exceeded the
wear limit.
The wear check gauge screwed by hand, without excessive force,
may enter into the thread gauge, but not more than one turn
of thread.
If it can be screwed in more than one turn of thread, the thread
gauge no longer meets the specifications. For direct working
of wear limits on pitch diameter, relevant specification guidelines
to be followed.
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Are all the functional parameters and features certified, when an used external micrometer is calibrated?
No.
Certain parameters like flatness of the measuring faces, parallelism
between the measuring faces and the measuring force, do not
remain the same as they were, when the micrometer was new and
not used
after being manufactured as per the applicable relevant specification.
The calibration of an used external micrometer certifies only
the instrument error of that micrometer. |
Whether Thread Gauges are repairable?
Not repairable due to intricate tolerances. |
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