I work quality control for a small manufacturing company. I am looking for information about making go/no go gages for inspecting bores on parts we manufacture. We have been moving into Lean manufacturing and six sigma. We are ID grinding the bores and the part moves to the next operation. The parts are in a constant state of movement so there is no time to check all the bores on the CMM. This is why we are looking into making Go/NO gages for checking 100% of the bores. In the past we did batch manufacturing and had time to check 100% on the CMM. If I have a bore of 3.1505 +.0005 -0, where can I find the information on what size to make the go/no go gage?

Below you can see a picture of what a gage might look like.  The procedure that I would recommend is:

Perform a capability study of a sample (30 ?) pieces that have been bored.  Use the maximum inscribed circle or cylinder method to measure the diameter.  That should give you the confidence that your process is delivering the desired results.  For example, a Cpk (or Ppk) of 1.0 should result in about 3 defects per 1,000. Then you can use a Go – No Go gage to tell you when there has been a change to your process.

The diameter of the smaller cylinder is the Go gage.  Diameter dimension is 3.1505 as measured on the CMM using maximum circumscribed cylinder.  The gage should pass through the length of the bore.  This side of the gage must pass through the hole.  If it does not pass through, the bore is too small. 

The diameter of the larger cylinder is the No Go gage.  Diameter dimension is 3.1510 as measured on the CMM using maximum circumscribed cylinder.  The gage should pass through the length of the bore.  This side of the gage must NOT pass through the hole.  If it does pass through, the bore is too large. 

A special thank you to Christine Henning, Inspection Supervisor at John Deere Horicon, for guidance on this reply.

Woody