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10Sep/10Off

White Paper on Resolving Measurement Disputes

Disputes over measurements can be costly for both parties to resolve and may hinder ongoing relations between suppliers and users of gages and instruments. Often it is simpler for both parties to agree to accept an average value of their readings as the final ‘size’ or the point at which their readings plus measurement uncertainties overlap.

The obvious way to avoid such problems is to agree beforehand on a method that will be used to resolve them if they arise. Often, the degree of separation between the readings dictates the best approach to take. Where the uncertainty of each party is significantly different, the party with the lowest uncertainty in the calibration would be considered more reliable.

The AMTMA offers the following methods as options you can choose from. If the Referee Method fails to bring a resolution, then the Universal Standard Method should be used due to the fact it is technically based and internationally accepted by metrologists in all disciplines.

The Referee Method

The two parties agree on a third party to provide a referee measurement that it is agreed will be considered as the actual value. An alternative on this is where the reading by either party that is closest to that provided by the referee is considered the accepted dispute.

Unless otherwise agreed to, the costs of using laboratories in this method are paid by the losing party.

The Unviersal Standard Method

National and international standards agencies have produced methods of resolving measurement disputes that focus on the uncertainty budgets of those that have produced measurements. The advantage of this method is that its technical base tends to remove personalities from the equation and may indicate that neither party to a dispute has the capability required to resolve it.

Using this method, the onus of proving a measurement falls on the party who has questioned the results of calibration. If requested, this party must provide a copy of their uncertainty budget for the measurement to the other party review. Budgets from both parties should be compared. Such a review should focus on seeking agreement between both parties respecting each element included in the budget since it will rarely, if ever, be all right or all wrong. The mathematics should take care of the rest. There may be cases where one or more elements have not been included in the budget included in the budget and when they are, the outcome changes significantly.

In the event one or more assumptions in the budget cannot be resolved, a third party can be asked to provide an opinion on them.

9Sep/10Off

No Go Gaging Per ANSI/ASME B1.2-1983 An American National Standard- How many turns?

One of the most frequently asked questions that we receive so here is the answer pertaining to unified threads. Please check the applicable standard for other types of threads as the acceptance criteria does change.

NoGo ( Lo ) Thread Ring Gage

A NoGo or Lo thread ring gage inspects the NoGo or Lo functional diameter limit of product external thread. The NoGo thread ring gage, when properly set to its respective calibrated thread setting-plug, represents the NoGo (Lo) functional diameter limit of the product external thread. NoGo (Lo) thread ring gages must be set to the applicable truncated or Hi-Lo setting plugs.

NoGo (Lo) thread ring gages when applied to the product external thread may engage only the end threads (which may not be representative of the complete product thread).

Starting threads on NoGo (Lo) thread ring gages are subject to greater wear than the remaining threads. Such wear in combination with the incomplete threads at the end of the product thread may permit further entry in the gage.

As stated in ANSI/ASME B1.2-1983, the “NoGo (Lo) functional diameter is acceptable when the NoGo (Lo) thread ring gage applied to the product external thread does not pass over the thread more than three complete turns.” The gage should not be forced. Special consideration such as exceptionally thin or ductile material, small number of threads, etc., may require modification of accepting up to 3 turns of the gage. It is highly recommended that a manufacturer not allow a maximum of 3 turns during thread fabrication as every thread ring gage is set slightly different to due the gage maker tolerances of setplugs and the subjective nature of setting adjustable style thread ring gages.

No Go ( HI ) Thread Plug Gage

The NoGo (HI) thread plug gage inspects the NoGo (HI) functional diameter limit of product internal threads. The NoGo (HI) thread plug gage represents the NoGo (HI) functional diameter limit of the product internal thread.

Thread plug gages when applied to the product internal thread may engage only the end threads (which may not be representative of the complete thread). Entering threads on product are incomplete and permit gages to start. Starting threads on NoGo (HI) plugs are subject to greater wear than the remaining threads. As Stated in ANSI/ASME B1.2-1983, the “NoGo (Hi) functional diameter is acceptable when the NoGo (Hi) thread plug gage applied to the product internal thread does not pass over the thread more than three complete turns.” The gage should not be forced. Special consideration such as exceptionally thin or ductile material, small number of threads, etc., may require modification of accepting up to 3 turns of the gage. It is highly recommended that a manufacturer not allow a maximum of 3 turns during thread fabrication as every thread plug gage may gauge differently due the actual size and gage maker tolerances allowed.

7Sep/10Off

Adjustable Thread Ring Gage Calibration: How Accurate Is It?

While a new AGD - American Gage Design adjustable thread ring gage is initially calibrated to a master setting plug gage, the setting can be slightly altered during the transport from manufacturer to end user. This can result from a variety of factors, ranging from a dropped adjustable ring gage to exposure to radical changes in temperature during the shipping process.The end result of these factors is that the locking assembly can shift, and if the adjustable ring gage is not shipped with a setting plug, the end user might never even know that the setting is no longer valid.

A gage arriving with an invalid calibration setting is not uncommon, and can be easily remedied if the setting plug is included or the end user has an existing setting plug. However, all too often, this is simply not the case. The absence of a set plug means that not only is there any way to check if the setting has shifted; it also means the end user will be unable to monitor the ring gage during its use or check after an accidental dropping or for intentional tampering. The end result may be a production run of bad parts.

Many manufacturers avoid the potential for liability by specifying that calibration settings only apply at the time and place of initial calibration. European manufacturers eliminate the potential problems associated with adjustable thread ring gages by using non-adjustable or solid style thread ring gages.

Additionally, calibration of AGD adjustable style thread ring gages by direct measurement is not authorized by ANSI B1.2 1983; Gages and Gaging for Unified Inch Screw Threads; Reaffirmed in 2007. Some calibration laboratories utilize the direct measurement method with ULMs or CMMs when a matching threaded master set plug gage is not available despite the above fact. This method fails to account for the helix offset alignment effect of adjustable style thread ring gages.

The only prescribed method of calibrating AGD – adjustable style thread ring gages is by means of a master thread setting plug gage. Per ANSI B1.2-1983; Reaffirmed 2007; page 40; paragraph 5.1.1: "Adjustable Go thread ring gages must be set to the applicable W tolerance setting plugs". Also reference table 5 page 17 for further evidence. Even more evidence can be found in Table 12 page 151. Also refer to Note 6 in the table as well.

When a thread master setting plug has not been purchased or is not available, the end user may opt to have thread ring gages calibrated by means of direct measurement so that they have a record for their files. This common practice by both accredited and non accredited labs may create more issues by improperly adjusting the thread ring gage out of tolerance and causing the end user to have a false sense of confidence in the gage based on a calibration cert.

Whenever an AGD – adjustable style thread ring gage is purchased it is always advisable to purchase or have access to the matching master thread setting plug gage. This practice will help to eliminate the possibility of using an out of tolerance thread ring gage. It will also reduce any costly downtime of having to send out a thread ring gage or order one in the event that the gage is dropped or mishandled.

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2Sep/10Off

Measuring Thread Measuring Wires

When you are calibrating thread plugs, thread setting plugs and AGD style thread ring gages it is important to know the correct size and proper constant of the thread measuring wires, as they provide the foundation for accurate thread gage calibration.Working thread plugs and thread master setting plug gages are calibrated by means of the three-wire method. The degree of accuracy in the results of your readings depends on the accuracy of the thread measuring wires. An error of one unit in the mean diameter of thread measuring wires will have a multiplying effect of three units in the pitch diameter of 60° thread plug gages.

1Sep/10Off

Introducing IN GAGE

Welcome to IN GAGE by Thread Check Inc. The main purpose of this blog will be to discuss the vast range of topics in gauging and measurement. IN GAGE will assist people involved with inspection and measurement to address common and complex questions and issues from the production floor to the temperature controlled calibration lab. Managers, machinists, engineers, quality personnel, and others concerned with gauging and measurement are all welcomed to ask questions and make their cases and opinions known.