I know from experience that a gage to check low limit of a hole must be a plus tolorance and high limit must be a minus tolorance. but where is this written so I can justify not using a minus tolorance pin as a go
I'm not sure if there was a typo in the previous answer as it appears to me that ANSI/ASME B89.1.10 is a standard for dial indicators, but you will find the statement referring to tolerance direction for plain plugs in ASME B89.1.5, Measurement of Plain External Diameters for Use as Master Discs or Cylindrical Plug Gages, Section 4.8, Tolerance Classes, where it states, "Unless otherwise specified, cylindrical plug gages are to have the tolerance all plus on the GO gage and all minus on the NOGO."
Simply put, the tolerances you have refered to are AGD standard gage maker tolerances needed to manufacturer the pin or ring. Classes are from "XXX" to "Z" with ""XX", "X", and "Y" in between. The highest precision is the XXX and of course the cost to manufacturer a pin or ring to this accuracy is cost prohibitive and seldom necessary unless your total tolerance on a part feature is less than 10 microns. If that is the case then you should invest in the tighter tolerance gage.
If my memory has not failed me, a NOGO Gage Pin for an M8x1.25 thread tap drill is somewhere around 6.812 mm. If this is true then a Z class pin would be manufactured to a tolerance of 6.809 to 6.812 mm. When you think about 3 microns being such a small percentage of the total tolerance for the tap drill, then this is both cost effective and more than acceptable. You never want to justify using a gage tolerance that does not guarantee an acceptable part. The gage maker tolerance on the go pin is just a sure method to change out the drill before reaching the part acceptance limit as the drill wears over time. I hope this helps your understanding about why part of the tolerance is used up in the manufacture of gages.
May your day be blessed with peace, hope, joy, and love.
Yes the AGD Standard is referred to in ANSI B89.1.10 The reference is the AGD standard is a guideline rather than a requirement. Best usage of the AGD standard is in the manufacture of the gages with your own quality plan allowing for a wider tolerance for gage calibration/verification criteria that makes sense for your organizations needs using a defined % of the part feature tolerance used up in the allowable gage tolerance. Of course the QS/TS auditor will not have issue with your gage tolerance so long as the gage can not accept a out of spec part condition. I hope this answers your question adequately.
Relation of Gage LImits to Part Limits
I'm not sure if there was a typo in the previous answer as it appears to me that ANSI/ASME B89.1.10 is a standard for dial indicators, but you will find the statement referring to tolerance direction for plain plugs in ASME B89.1.5, Measurement of Plain External Diameters for Use as Master Discs or Cylindrical Plug Gages, Section 4.8, Tolerance Classes, where it states, "Unless otherwise specified, cylindrical plug gages are to have the tolerance all plus on the GO gage and all minus on the NOGO."
Karl Bly
Gage Maker Tolerances
Simply put, the tolerances you have refered to are AGD standard gage maker tolerances needed to manufacturer the pin or ring. Classes are from "XXX" to "Z" with ""XX", "X", and "Y" in between. The highest precision is the XXX and of course the cost to manufacturer a pin or ring to this accuracy is cost prohibitive and seldom necessary unless your total tolerance on a part feature is less than 10 microns. If that is the case then you should invest in the tighter tolerance gage.
If my memory has not failed me, a NOGO Gage Pin for an M8x1.25 thread tap drill is somewhere around 6.812 mm. If this is true then a Z class pin would be manufactured to a tolerance of 6.809 to 6.812 mm. When you think about 3 microns being such a small percentage of the total tolerance for the tap drill, then this is both cost effective and more than acceptable. You never want to justify using a gage tolerance that does not guarantee an acceptable part. The gage maker tolerance on the go pin is just a sure method to change out the drill before reaching the part acceptance limit as the drill wears over time. I hope this helps your understanding about why part of the tolerance is used up in the manufacture of gages.
May your day be blessed with peace, hope, joy, and love.
Relation of gage limits to part limits
It is not that I don't understand the reasoning behind this method. What I need to know is where this rule is written ie. an ANSI spec.
ANSI B89.1.10
Yes the AGD Standard is referred to in ANSI B89.1.10 The reference is the AGD standard is a guideline rather than a requirement. Best usage of the AGD standard is in the manufacture of the gages with your own quality plan allowing for a wider tolerance for gage calibration/verification criteria that makes sense for your organizations needs using a defined % of the part feature tolerance used up in the allowable gage tolerance. Of course the QS/TS auditor will not have issue with your gage tolerance so long as the gage can not accept a out of spec part condition. I hope this answers your question adequately.