How to Measure Counterbores And Blind Holes with Air Plug Gages

Air plug gages

Air plug gages are used to perform a
variety of tasks around the workshop. Some of these tasks include measuring
blind holes (also known as counterbores). An air plug gage is made up of a
cylindrical body that provides the guide for air jet positioning in the bore.
The nozzles that release the air are contained inside this body and this
essentially makes the air plug gage a non-contact measuring tool. The internal
nozzles also help to protect the air jets from being damaged. Air plug gages
also clean out the surface of the object being measured through the air jets,
leading to greater accuracy when measuring. So, how does one use these air plug
gages to measure blind holes?

Blind Holes

When measuring blind holes with an air
plug gage
, one must ensure that the hole is free of any contaminants.
Debris and pieces of wood or metal in the blind hole can lead to false readings
from the air plug gage. One must also ensure that they are using the right size
of the tool and that the gage is properly maintained. Typically, the air jets
clear most of the debris away but it is useful to regularly inspect the nozzles
to ensure that they are clean.

When using air plug gages, the gage will
automatically center itself in the hole being measured and reduce (if not
completely eliminate) the probability of angular error. This makes the gage easier
to use for operators who have limited experience in using air gages.

Note of Tolerances

Apart from selecting the correct air plug
gage for the blind hole you want to measure, there are a number of things to be
on the look-out for. The first is to be aware of the tolerance that you are
measuring for.

Consider Different Surface Finishes

The other thing is to be aware of the
surface finish of the blind hole that you are measuring. Various surface
finishes can give different readings. This is because the air plug gages
measure the average of peaks and valleys that the air jets encounter.

Avoid Rushing to Take Measurements

The other thing to note when using air plug
gages to measure blind holes is to be patient with the readings. This is
because all air gages measure the backpressure created by the air inflows that
‘bounce off’ the part. If the backpressure takes a while to fill up, then
taking a reading immediately will probably give you bad results. This is
unlikely to be a problem when measuring blind holes in a simple workshop but if
this is happening as part of an automated manufacturing process, then bad
timing can result in wrong results.

Air plug gages are effective in measuring
blind holes provided that they are used properly. Willrich Precision Instrument stocks a
variety of high-quality air plug gages for all your precision measurement needs.

by George Chitos

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