|
Ten questions to ask when buying ring
gages
To determine whether the ring gages you're considering
will best meet your requirements, you need to ask the right
questions.
While the quality of cylindrical ring
can vary depending on the manufacturer, customers often treat these
gages as commodity items. As a result, the primary question that
customers ask is, "What is your price and delivery?" In reality,
that should be the last question asked.
Here are several questions you should pose first, to ensure that
the gages you purchase truly meet your company's requirements and
industry standards.
What material is used to manufacture the ring gages?
It is important that the ring-gage material be stable and hard.
Good-quality tool steels such as 8620 or O6 are appropriate choices.
Steel blanks should be heat treated to a minimum of 62 Rc.
Do you inspect incoming material for adherence to
hardening specifications?
The material is the foundation of ring-gage quality, so the answer
should be an emphatic "yes."
After heat treating, do you stabilize the material?
While heat treating helps stabilize steel blanks, subsequent
grinding operations can affect the material by introducing heat and
stress. A quality-conscious gage manufacturer will eliminate
material fluctuations entirely by putting blanks through a
stabilization process, which involves cycling the rings through
temperature extremes from -130 F to 300 F. Further, flange-type
rings should be stabilized again after grinding.
Are your gages precision lapped by hand?
Lapping is the process in which minute amounts of material are
removed to bring the ring to final size and within tolerances. It is
the final process in ring manufacturing, and extremely critical. It
requires a highly skilled person who has learned to "feel" a
millionth of an inch. No automatic lapping machine comes as close in
accuracy and precision as a person who has mastered the art.
Unskilled lapping can result in rings with excessive out-of-round or
tapered conditions.
Do you inspect your gages in a temperature-controlled
metrology laboratory?
Although rings are inspected for size and class in a
temperature-controlled lapping room, it is important that final
inspection occur in a separate, environmentally controlled metrology
laboratory. In addition, the master set of gages used in the lab
should be traceable to the National Institute of Standards and
Technology (NIST), Gaithersburg, MD.
What is the sampling of the gages you inspect?
To ensure the utmost integrity, every ring should be inspected
before it is shipped to the customer.
Will you certify my ring gages?
This is becoming more important as International Organization for
Standardization (IS 0), Geneva, Switzerland, and other
quality-improvement programs demand gage calibration and tracking
documentation. Make sure your ring-gage manufacturer has
documentation systems in place to certify, track, store, and update
gage information.
Do you certify both class and size?
Both types of certifications detail the standards followed and
include NIST-traceability statements for the laboratory. A
Certification of Class simply states that the ring has been
inspected and found to be within the tolerance band of the class
that is marked on the ring. A Certification of Size provides actual
size deviations from nominal for calibration points in two axes and
three planes for each axis, for a total of six readings.
Does the certification contain a Statement of
Uncertainty?
A properly prepared certification should also contain a Statement of
Uncertainty for the readings given.
What is your price and delivery?
Only at this point, when you've received answers to the previous
nine questions, is it an appropriate time to ask this final
question.
|
