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In my understanding, there may be little difference between a working or production gauge and an inspection gauge. The difference is (usually) primarily in the way that they are used and handled.

A working (or production) gauge is use in actual production of products. As such, it is subject to a lot of handling and possible abuse in application. For this reason, it may be more robust in construction than the comparable inspection gauge.

The inspection gauge is used only in the metrology laboratory where it is handled with care and can be checked against primary standards. It usually cannot be adjusted except by those with special qualifications and permissions.

There may be other differences as well. For example, a plug gauge to check the size of a hole may be simply a go/nogo gauge (if one end will enter the hole, it is large enough; if the other end enters the hole, it is too large). In contrast, a gauge intended to determine the actual size of the hole has to in some way adapt to the hole being measured.

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Umama,

I can agree that the shop guage should fall inside the work tolerance, but how can you justify saying that the inspection guage should fall outside the tolerance? Would this not mean that the inspection guage accepts (passes, approves) work that is actually outside of the tolerance limits in some cases?

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Umama, the more I think about it, I think I have to disagree with both of your statements. I discussed my objection to one in the previous note; in this note, I will explain why I object to the other.

You said, "The workshop gauge are arranged to fall inside
the work tolerance..." This would indicate that the shop guage is going to reject some product that is still within tolerance. I don't think many employers will accept that idea. Why would you reject material that is within tolerance?

Most manufacturers want to produce and ship as much product as possible, consistent with their contract. To reject material that is within the spec is contrary to that objective. They would not allow such a guage to exist.

In short, both shop and inspection gauges should be as close to accurate as possible, at least an order of magnitude better than the tolerances.

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There are three systems in Gauge Design:

The above design which I mentioned falls under the first system.

Whereas in the second system, i.e, the revised system, the tolerance zone of workshop gauge was kept the same and the inspection gauge tolerance zone was reduced due to the disadvantages in the first system and and as it was correctly questioned in your comment, because it led to rejection of material within tolerance. Also both the gauges had to be made seperately due to the difference in their tolerance zone.

In the third system, which is the present British System, the tolerance zones were adjusted so as to result in satisfactory function and production. It is based on the Taylor's principle and no work is accepted that falls outside the mentioned limits. This dispenses the use of two seperate gauges and same tolerances are provided on both the type of gauges.

Thus this modern system does not give any difference to both the types of gauges.

The above question is thus based on the evolution of gauge design.

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In precision engineering, an inspection guage defines the precise tolerances of the finished product. These dimension checks are carried out in a room in which the ambient temperature is accurately controlled to eliminate measurement variation caused by expansion/contraction of the workpiece.

Workshop guage tolerances must fall within the inspection guage tolerances in order that the workpiece is of the correct design dimensions at final inspection. The amount that the workshop guage tolerances fall within inspection guage tolerances must, for example, take account of the day-to-day ambient temperature variation in the shop floor environment.

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Inspection gauges have no common adjustment are set by precision Johansson gauge blocks.  Work shop gauges (micrometers and verniers) are recalibrate periodically and color coded also using Johansson gauge blocks.  Both are done in controlled environment by a qualified person.

 

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