Comparing Gauge Blocks - Translating the calibration between the master set and the QA set

[grnfish]

Hey,

I am trying to determine the best course of action for my calibration plans.

I am anticipating getting Grade 0 or 1 for my 'Master Block'. The quantity would be two or three blocks (maybe more). Then use some sort of 'gauge comparator' to calibrate to a QA set Grade 1 or 2 blocks which will be used for calibration. I was also hoping to use this device to translate the 'Master Block' to my sets of XX or XXX gauge pins also.

Does anyone know of an instrument with a good way of translating the calibration between the master set and the QA set? Or is there a better approach all together?

Pratt and Whitney make some instruments such as the Laser Ruler.

Opinions welcomed, cheers

 

[dwperron]

When you start dealing with gauge blocks and class XXX pins you are moving into areas of metrology where allowable errors are very small. Also I am assuming here that you are dealing with ASME B89 tolerances, better referred to as Grade AS-1 and AS-2. At 1 inch the maximum deviation for your blocks would be ±6 µin for Grade 0, ± 12 for AS-1 and ±24 for AS-2 which, for gauge blocks, are fairly wide tolerances. For the XXX and XX pins the tolerances are 15 and 30 µin, similar values. You could use a machine like a Pratt and Whitney Labmaster to compare these "master" blocks to your working sets, adding an uncertainty of about 4 µin for every inch of difference between your master block and the block being measured.

Another very large consideration would be temperature stability. Tool steel has an expansion coefficient of about 12 µin/in/°F, so if the 1 inch master block and the block being measured are 2°F apart in temperature there could be a 24 µin difference in the measurement. That's why strong environmental controls are needed for hard gauging, why you need to lets tools "soak" to stabilize at lab temperature before calibration, and why you need gloves and shields to prevent body heat from affecting measurements.

In the metrology world you typically would use a "grand master" gauge block set to compare to sets being calibrated. The one to one size comparison can reduce you measurement uncertainty. There is a lot involved in calibrating gauge block sets, so unless you have a number of sets you should probably send them out to the experts who specialize in this field.

 

[grnfish]

Thank you for the reply

Currently creating a plan (that will span the next few years) to establish a high end metrology laboratory within our company's facility. I do understand the importance of a controlled environment and the small room for error when preforming these procedures, after consulting the NIST gauge block text available on the internet (along with other sources). I have continued researching the appropriate ways of going about this task. I suppose since this is new territory for the company (and me), I have come to the forum with questions I will eventually (hopefully) answer myself -- but always looking for quick opinions and inputs since Google does not always provide resources with a black and white answer (welcome to the real world)

Enjoy