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NPT-L1 Work Ring Gage Calibration

How to use NPT Master Plug Gauge to Calibrate the NPT-L1 Work Ring Gage

The best situation is for the gauge maker to have your NPT Master Plug Gage at his plant when he makes the NPT-L1 Work Ring Gauge. The NPT-L1 Work Ring Gage will be matched to your NPT Master Plug Gauge. This may not be cost effective. Expect a calibration fee for your NPT Master Plug Gage. Expect a fee for matching the NPT-L1 Work Ring Gauge to your NPT Master Plug Gage. Expect a longer than normal lead-time. Once the new NPT-L1 Work Ring Gauge is received in your plant, calibrate it and record your initial reading for comparison at subsequent calibrations.

An optimum situation is for you to have the NPT Master Plug Gage in hand when the NPT-L1 Work Ring Gauge is new. Once the new NPT-L1 Work Ring Gage is received in your plant, calibrate it and record your initial reading for comparison at subsequent calibrations.

Calibration Procedure:

  1. Clean NPT-L1 Work Ring Gauge and NPT Master Plug Gage to remove any foreign objects.
  2. Inspect the NPT-L1 Work Ring Gauge for nicks or damage on the threads.
  3. Lubricate the gages with light oil.
  4. Assemble the NPT-L1 Work Ring Gage onto the NPT Master Plug Gauge with hand tight pressure.
  5. Take a measurement from the NPT Master Plug Gage Basic Notch to the NPT-L1 Work Ring Gauge Large End Face.
  6. Record this measurement in your calibration record.

NPT-L1 Work Ring Gage with NPT Master Plug Gage

Evaluation of the measured results:

  1. For newly purchased NPT-L1 Work Ring Gage, or a used NPT-L1 Work Ring Gauge with no initial calibration result, it is acceptable if measured result is +/- one third of a turn from the NPT Master Plug Gage Basic Notch.
  2. For a used NPT-L1 Work Ring Gauge which has an initial calibration recorded, it is acceptable if measured result is +/- one third of a turn from the recorded new NPT-L1 Work Ring Gage initial measurement result.
  3. If there is not new NPT-L1 Work Ring Gauge initial measurement result, then NPT-L1 Work Ring Gage is acceptable if measured result is +/- one third of a turn from the NPT Master Plug Gauge Basic Notch.

What to do about nicks or damage:
If a NPT-L1 Work Ring Gage is damaged the most reliable and least expensive course of action is to replace the gauge. Making a repair locally is impractical and costs associated with having a gage maker repair the thread will total to more than a simple replacement. If time is critical, and a replacement NPT-L1 Work Ring Gauge is not available, the offending damage may be removed with a small hand-held grinding wheel. Repair which results in a void in the thread form is acceptable if not at large end of NPT-L1 Work Ring Gauge. Calibrate the NPT-L1 Work Ring Gage after any repair attempt to assure that the calibration result is within acceptable range.

How much is one third of a turn?

  1. For 27-TPI one third of a turn is 0.0123”
  2. For 18-TPI one third of a turn is 0.0185”
  3. For 14-TPI one third of a turn is 0.0238”
  4. For 11.5-TPI one third of a turn is 0.0290”
  5. For 8-TPI one third of a turn is 0.0417”

Notes:

  1. In case you wish to check my math; one third of a turn = 1"/TPI/3.
  2. When we speak of one third of a turn, we are not talking about rotational distance. We are referring to the linear distance along the center line of the thread which is made apparent when comparing the NPT Master Plug Gage Basic Notch to the NPT-L1 Work Ring Gauge Large End Face.
  3. The L1 designation is the only option for a NPT Work Ring Gage. The L3 designation is only appropriate for NPTF or ANPT. Because the L1 is the only designation for a NPT Work Ring Gauge the designation need not be stated, but to state the L1 is encouraged and considered attention to detail.

Disclaimer:
The above calibration procedure is not the official calibration procedure; however; it is a shop expedient method of control and calibration of your NPT gages. If using the official calibration procedure is important to you; or if you are a calibration laboratory selling calibration services to others; purchase B1.20.1 and follow the instructions therein. Each size has specific charted values to be applied in the calibration procedure. In the end you must decide which procedure you will use and that decision may have to be justified to your management/customers.

Comments:
Original Posting: 1/7/2012
Last Revision: 5/8/2014
Error corrections in or comments about the above data can be sent to: gageguy@gagecrib.com

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