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22Mar/12Off

Choosing The Correct Air Gage

Choosing the Correct Air Plug Gage

There are two basic styles of Air Plug Gages. Through Hole Style and Blind Hole Style. Dimension B on the attached form refers to the dimension of the jet centerline to the nose of the air plug. The overall dimension is indicated by Dimension “A”. If you are measuring a blind bore you must order a Blind Style air plug so the air escapement channels are designed to allow for air to escape the part, regardless of the depth of the bore. There is also an option for a Super Blind Plug which further reduces dimension B permitting checking closer to the counterbore, or the bottom of the part. If extra length is required and an extension or handle will not work, you can specify extra length in 1” increments. Non-Relieved style should only be specified for valve bores where obstructions like lands could make it difficult to remove the tool. You must also specify the dimensionair Model Number you are ordering the tooling for. It is always recommended to supply a part drawing with your inquiry.

https://www.threadcheck.com/images/pdf/Air-Plug-Form-2.pdf

Choosing the Correct Air Ring Gage

Special care must be taken when selecting air ring gages. There are 5 basic styles of air ring gages. The 5 styles are centered jets, offset jets, shoulder type, countered bore type, and snout type. Air rings may be attached directly to the Dimensionair, or used with base and guide chutes that can only be provided at time of manufacture. It is always recommended to supply a part drawing with your inquiry.

https://www.threadcheck.com/images/pdf/Air-Ring-Form.pdf

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6Mar/12Off

Measuring Plain External Diameters – American vs European

A case related to pin gages being rejected by our European Customer

The ASME B89.1.5-1998 is the correct document to review. Reference para. 6.1, pg. 5 & 6 as well as Table 4 on pg. 7. The values were computed using the equation in Puttock and Thwaite’s CSIRO Technical Paper #25. This statement is also on page 6. The question that should be asked is, what is their measurement uncertainty? Remember that the Europeans add measurement uncertainty into their measurements. We do not do that in the US. Depending on the uncertainty budget, they may not have the accuracy to measure a .000020” gage. Our measurement uncertainty is .000012” based on our latest accredited calculations . This is not good enough to accurately measure a Class XX pin. Our customers accept our measurements as long as our uncertainty is stated on the calibration certificates. According to ANSI/NCSL Z540 & ISO 17025 the total uncertainty of the measurement should not exceed 4:1. That would require a total measurement uncertainty of .000005”. The only lab that I know of that can measure this accurately w/in the 4:1 Rule, and prove it, is NIST.

See the link to the NIST web site that has a calculator to assist in the measuring force calculation.

http://emtoolbox.nist.gov/Elastic/Case10.asp

Note: The measuring force changes with the diameter of the part being inspected.