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FAQs

The standard in the field says that any variation found within the data from a gage R & R study that falls below 10% is acceptable. Once above 10%, but still below 30% variation, your system may still be used, but only under specific circumstances where addressing the issue is not possible at that time. With a variation above 30%, you should no longer be using your measurement system, as some part of it needs immediate attention in order to assure accuracy. The variation found by a gage R & R study is calculated using a ratio of the precision of the measurement system to the tolerance of the manufacturing process.

A telescopic bore gage measures the size of a bore through indirect methods. Essentially, the telescopic bore gage is used to take the size of a bore, and then an external tool, such as a caliper or a micrometer, is used to measure the output of the gage. The head of the bore gage is extended at an angle within the bore and locked into place. The extended head is the part that is measured to get the final output. Very similar to inside calipers, which can also be used to measure bore diameter, telescopic bore gages have the added advantage of being able to be locked in place during the measurement process, thus ensuring higher accuracy. Telescopic bore gages are used by mechanics and anyone in metrology that needs to find the interior diameter, radius, or circumferences of a pipe or a hole.

The repeatability measured by a gage R & R study refers to the variability in measurement which results when one individual measures one part using one gage. In other words, when one operator measures one part using one gage again and again, the resulting changes in measurement are due to an error that is occurring within the equipment. While infinitesimal repeatability issues are going to be expected, a gage R & R study can root out more serious inconsistencies. Testing repeatability is an important part of gage R & R studies, and it is what tells you that your gage is imprecise and requires attention.

The reproducibility measured by a gage R & R study refers to the variability in measurement which results from the irregularities of the operator. Reproducibility is tested by having multiple individuals measure the same part using the same gage. In this way, a gage R & R study can adequately determine if there is variability due to the individuals measuring the product, rather than the measurement process or equipment itself. The reproducibility is necessary to know how much variation results when different operators use the same equipment. Just as it is important to know that your equipment is functioning well, it is necessary to know how individuals are impacting the measurement process of a larger manufacturing system.

Small hole bore gages come in two main types: full-ball and half-ball bore gages. The terms full- and half-ball refer to the end of the bore gage that is inserted into the bore to complete the measurement. This end is typically opposite to the knurled knob used for setting the anvils. Full-ball small hole gages are generally simpler to set the anvils on and lock into place. More often than not, these bore gages will provide a more accurate and precise measurement of a bore. Half-ball gages are more prone to springing during measurement and require a more experienced user. Half-ball bore gages are more likely to result in an inaccurate measurement. However, some machinists prefer half-ball bore gages because they allow the user more control and leave room for adjustment in unusual measurement circumstances.

The type of bore gage required will vary depending on the measurement job at hand, as well as on the preference of the user. Dial bore gages are often an excellent choice when needing to conduct a highly precise measurement of a bore. The biggest benefit of the dial bore gage is that it does not require the transferring of the measurement to another tool (micrometer or caliper), but rather has a built in mechanism so that a bore can be measured directly. In general, dial bore gages are both highly accurate and highly fast. Additionally, a dial bore gage comes in handy if the user needs to assess a bore for wearing or tapering that could impact the roundness and symmetry of the bore. Dial bore gages come with a very high resolution, usually reaching an accuracy of 1/100 of a millimeter or 5/10,000 of an inch.

Gage R & R studies are vital to determining the amount of variability within a measurement system. Knowing the magnitude of the variability within a production line allows you to ensure that your measurement system is running smoothly and producing accurate results. In the world of precision measurement, exactness is everything. Should you find after completing a gage R & R study that the variability is too large, you would know for sure that you could not use your system as it is, and that you need to adjust it in some way. Knowing that there is an issue is the first step to fixing it, and making you a better manufacturer. Constant vigilance with the accuracy of your measurements can be accomplished using regular gage R & R studies.

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