Thank you Walter for your reply.
The real problem I have with AMS2430 3.11.1 is with the “.003 whichever is greater” part of the rule.
If we are to consider why we ultimately need the N strip it is indeed a resolution issue. 4A is the last intensity on the A scale that the Almen gauge has resolution to measure using the 30% rule (for those drawings that state only a minimum Intensity). The 30% rule sets the arc height limits for 4A at .004” to .005”. The difference between the upper and lower limit is .001”. The Amen gauge has a resolution of .0001” therefore using the “rule of tens” from metrology the gauge is capable here but it is the lowest A scale intensity it is good for. So we transition to the N scale which, because it is thinner, bends approximately 3 times as much as an N strip when exposed to the same shot stream conditions. The interesting point to make here is that the Almen gauge is capable to measure the .001” tolerance proposed by the 30% calculation from the minimum 4A. So why grant a tolerance expansion to .003 using the “or .003 whichever is greater” portion of the AMS2430 3.11.1 rule. This makes no sense to me and also unfairly punishes N strip use in these intensity ranges (ranges near the upper limit of the N scale) verses the use of A strips at the lower end of the A scale.
Now let’s look at the 30% rule with regards to N strip measurement. Using the 30% rule of AMS 2430 3.11.1 The Almen gauge again is capable of measuring down to 4N as the arc height limits calculated here are .004” to .005”. Now we have a problem at intensities below 4N. The gauge is no longer capable. Here and only here would would it make sense to offer an “or” to the 30% calculation of AMS2430 3.11.1 and that “or” would not definitely not be “or .003 whichever is greater”. It would be “or .001” whichever is greater”.
In both cases the cutoff for capability of the the Almen gauge for the 30% rule is 4 but perhaps it is not only the Almen gauge resolution that is a factor. Perhaps it is the repeatability of manufacturing the strips themselves. If we to propose a .001 tolerance between the upper and lower limits of either strip perhaps the manufacturing process of the strips themselves would make that tolerance unrealistic/unachievable. Is this the real reason we have this “or .003” whichever is greater” portion of the rule? Is it the strips? .003” seems large to me if this is indeed the case.
Thanks again to anyone who can help me reconcile this portion of AMS2430 in my mind.
SlYdEr
