fitted. If proper lubrication is neglected, they wear
rapidly and fail within a short time.
Internal threads are cut with taps and tap
wrenches. External threads are cut with dies and die
a light machine oil. Since the compressed air comes
stocks. All threads are not alike. They must be
directly in contact with these parts, it has a tendency
designed, selected, and cut to fit the job. As an HT,
to drive the lubricant out through the exhaust.
you will be concerned with two types of threads:
Therefore, when working steadily with any pneumatic
machine threads and pipe threads.
tool, you should regularly check the lubricator. Make
Dies and taps for cutting machine threads are now
certain there is plenty of lubricant, and empty the filter
made according to three basic sets of standards:
assembly when needed. On low-pressure compressed
American National, American Standard, and Unified
air systems that do not have the filter, regulator, and
Thread Standard (also referred to as "the standard").
lubricator assembly, you should disconnect the air
Knowing just what these standards are is important.
hose every hour or so and squirt a few drops of light
oil into the air hose connection. Heavy oil will cause
The AMERICAN NATIONAL standards were
precision parts to clog up and fail. If this happens, you
widely used for many years. There are two series of
American National machine threads with which you
will have to clean your tool in cleaning solvent to
will be concerned. These are the American National
loosen the gummy substance. Then blow out the tool
Fine (NF) and the American National Coarse (NC)
with air, lubricate it with a light oil, and go back to
series. The form of the thread is the same for both
National Fine and National Coarse; the difference is
Keep your pneumatic tools clean and lubricated,
in the pitch or number of threads to the inch.
and you will have fewer operating troubles.
The second set of standards for threads is the
When using portable pneumatic power tools, there
AMERICAN STANDARD. The American Standard
are certain safety precautions that you must observe.
threads for machine screws are based on the older
American National Standard. The two sets of
Always wear your goggles and hearing pro-
standards are not identical, but some of the American
tection when working with these tools.
Standard threads are identified by the old American
National designation. For example, the American
Take care not to allow any of these tools to run
Standard Fine series is designated by NF and the
out of hand. The pneumatic grinder especially
American Standard Coarse series by NC.
will want to "walk" away from the point you
want to grind.
The third set of standards is the UNIFIED
THREAD STANDARD. This standard was agreed to
Always stand so that your feet won't slip
by the United States, Canada, and the United Kingdom
while you are working. Make sure that you are
in 1948. It is expected that the Unified Thread
Standard will become the generally accepted standard
for machine threads, replacing the American Standard
Apply the grinding wheel to the work with
and the American National.
gentle pressure. Sudden forcing may cause the
wheel to shatter. As you complete the work,
Many of the machine threads using these three
ease up on the pressure.
basic standards are interchangeable; they are either
identical or very similar in general form. The major
Be careful not to allow the air hose to become
differences between the Unified Thread Standard and
the earlier standards are in the application of
allowances, the variation of tolerance with size, the
Pneumatic grinders and sanders turn at a high
amount of pitch diameter tolerance, and the
rpm. Use only the approved type of grinding
designation of the threads. In general, the Unified
wheel or disk. The maximum operating rpm is
Thread Standard provides more classes of fit than did
shown on the side of the wheel or disk. Re-
the earlier standards.
member the rpm rate of the wheel must be
higher than the rpm rate of the grinder or
Pipe taps and dies differ from machine taps and
sander. Using a wheel with a lower rpm rate
dies in that most pipe threads are tapered to provide
than the tool can cause the wheel to shatter.
an airtight and liquid-tight seal. Pipe diameters are