Hello all,
I am in the process of expanding the capabilities of our 17025 lab to include dimensional calibrations. I have a couple of questions regarding equipment and standards.

1. What is the best (easiest) way of certifying gage blocks? Horizontal "universal" type machine or vertical comparator? Keeping in mind that I could also do other various gages on the horizontal "universal" machine. I want to be able to do gage blocks up to 20". I realize that once I get over 4 - 5", most vertical comparators wouldn't work. Could I then go to a height gage for blocks in the range of 5 - 20"?

2. What are the benefits of purchasing high grade gage blocks for use in an environmentally controlled lab when I use the correction values of my standards when determining the error for tested items? I could spend $500,000 trying to get gage block standards that have zero error but if I am using the correction values stated on the certificates in my calculations, what's the point?

Forgive my ignorance on this subject. I am trying to educate myself as much as possible before spending the money on equipment and standards. I don't want to over spend for something I don't really need, but I don't want to be stuck with insufficiant eqiupment & standards either.

Any help on this is GREATLY appreciated. I have some follow up questions as well, but I want to take this a step at a time.

dan

Daniel, first... there is no ignorance of any kind in your query. It is actually a very good question.

As for measuring gauge blocks, I am not the best on that. Wesley and several others here have better knowledge on that than I. Are you going to buy profile equipment for this? That equipment is expensive. However in general, you "zero" out the higher-order standard measure, then calculate the deviation of the U.U.T.

As for the proper gauge blocks... purchase the best you can afford. Don't get three levels higher than your need; you'll have to take a loan out and them to N.I.S.T.:tg: Saying if you purchase standards with the appropriate accuracy ratio, you will not have to worry about using the correction factors, because they will be insignificant. The gauge blocks will change over time; you want that change insignificant as possible.

I have worked with standard situations where we were having to put correction factors and such on the test sheet (actually, they were mass standards). That really got to be a pain, and caused problems. When we got the correct standards, life got better.:D

Too, the better gauge blocks are made with better material, and given appropriate storage/environment, they will serve you well.

NOTE: If I remember correctly, you are in the mass standards/balance business. Just like with classifications of weights, top grade blocks will need to be stored properly.

This is just a gut thing with me... always purchase the best you can afford. You never know what business needs you'll need down the road. You can always have your blocks certified to a lower grade than they are actually rated for, if it is cost-prohibitive.

One more thing... budget to have something to cover your blocks while they are out for calibration.

The first question to ask yourself is how accurate do you want to be when calibrating gage blocks? What kind of uncertainty to you hope to achieve?

Do you need to be the most accurate guy in your area? For example: In my area, there is one guy whose uncertainty is 5 uin at 1 in. There is also Starrett whose uncertainty is 2 to 4 uin at 1 in.

We have a Pratt & Whitney LabMaster Universal which can be used for gage blocks, rings, plugs, thread plugs, length standard up to 12". If you go to A2LA's website, and search for this piece of equipment you will find uncertainties anywhere from 3 to 10 uin at 1 in (I suppose this fact could be talked about in another thread as to consistency in the measurement community). My uncertainty budget works out to 8 uin at 1 in.

If a customer wants to choose the guy in town who has a 5 uin unceratinty instead of my 8 uin uncertainty, I ask the obvious question: "If 3 uin matters, why not go to Starrett?

The labmaster universal requires only a few master gage blocks as it is a long range comparator. you can master with a 0.1 in and 1" block and test anywhere in the range. This makes your gage block purchase much less and your annual calibration cost of those blocks less. You can also purchase two sets in which case you are never out of business when your blocks go out for calibration. Also, the time required to calibrate a set is less than making a compariosn at every point.

Whatever you do, I would suggest trying to calcualte your uncertainty budget prior to getting the equipment. Of course, things like repeatability would have to be estimated, but you can get a good idea if the uncertainty will be what you need before you spend the money.

Total cost estimate: We took a small room and installed a Leibert Precision Cooling system with Electirc Reheats to control temperature and humidity. We put in clean room ceiling tiles and used vapor barrier paint. Purchase of LabMaster with all the fixtures and master gage blocks and modification to room was about $125K.

This does only get you to 12". How much work do you really think you would have over 12"?

I hope this helps.