Is there a master gauge block?

[turnworks]

Pretty dumb question but it got me thinking.

If I use a mic I need to check it against a gauge block or standard to make sure its accurate. To go farther I need to send in the block or standard to get it calibrated. At that shop do they rely on another tool to check my block? What block do they use to check their tool before checking my block? Is that the same block that other cert places use? And on and on it goes.

Was just curious.

 

[eKretz]

Generally they use blocks that are kept in air conditioned environment and treated like princesses. Over a year or whatever length of time they likely send those out to be compared to NIST standards.

 

[Donkey Hotey]

Truly a rabbit hole of a subject. This is a very down to earth video that still covers quite a bit of depth. Well worth the watch.

 

[PeteM]

Where it ends (today) is with length defined by the distance traveled by light in a vacuum in an absurdly short fraction of a second. In between, all manner of proxies, including the standards eKretz notes above.

If you're just satisfying yourself, a decent set of gauge blocks for measuring a mic at various points and an optical flat to check parallelism of the anvils will do for all practical purposes.

What's kind of cool is that we just decided on a new standard for the kilogram - based on Planck's constant. Far as we know, that one won't have to be updated.

 

[stephen thomas]

You can still find P & W/GE Electrolimit machines at school auctions. Mine cost $15.

Interesting for comparing roundness/lobing depending on fixture (angle of Vee block), or a gage stack against an individual block and other fun relatively low useful but informative explorations.

Of course you still need that Master, Master block.
Though the last inspection report with the blocks, and a SWAG as to whether it was used or worn since, is a good start for local measurement at a given temp.

 

[plastikdreams]

I believe nist has a large collection of "the" standards...how "they" calibrate them is probably some kind of electrical and mechanical wizardry and a bit of magic lol

 

[Ohio Mike]

For those that really want to go down a rabbit hole the YouTube channel Machine Thinking has rare behind the scenes look at NIST's Moore M48 CMM.

 

[Donkey Hotey]

For those that really want to go down a rabbit hole the YouTube channel Machine Thinking has rare behind the scenes look at NIST's Moore M48 CMM.

Yep, that's another great video on the subject. Nothing like watching that to lose all confidence in your measuring tools and processes.

 

[Stirling]

Pretty dumb question but it got me thinking.

If I use a mic I need to check it against a gauge block or standard to make sure its accurate. To go farther I need to send in the block or standard to get it calibrated. At that shop do they rely on another tool to check my block? What block do they use to check their tool before checking my block? Is that the same block that other cert places use? And on and on it goes.

Was just curious.

Buy this book. Worth the read down a deep rabbit hole

EDU-102-10: Metrology Handbook eBook (2nd US edition) by Nobuo Suga - Mitutoyo

The Metrology Handbook is a modern reference book for the dimensional metrology and inspection field. The 280 page full color book was written by Mitutoyo America’s own Nobuo Suga. The entire book is available for viewing in the eLearning platform at no cost.

www.mitutoyo.com

 

[winger]

I read Moore's book a quite a few years ago.
Foundations of Mechanical Accuracy.
Looks like the machine in the video has added even more decimal places to the original machines by replacing the screw with lasers. Interesting that it is now metric when I believe the screws on the original machines were made in inch.
One thing the video missed was that the temperature control room was designed to maintain almost no difference top to bottom of the room.

Is this particular machine a one of a kind?

Dave

 

[jccaclimber]

I read Moore's book a quite a few years ago.
Foundations of Mechanical Accuracy.
Looks like the machine in the video has added even more decimal places to the original machines by replacing the screw with lasers. Interesting that it is now metric when I believe the screws on the original machines were made in inch.
One thing the video missed was that the temperature control room was designed to maintain almost no difference top to bottom of the room.

Is this particular machine a one of a kind?

Dave

AFAIK NIST has two of them, but there's a listing for one on a used machinery page so there might be a few others out there. I wouldn't be surprised if the NIST one has a few $$$$ upgrades that the others do not.

Edit, I found one article that claims 5 were made.

 

[specfab]

In many respects, for getting a generally true representation of gage R&R (repeatability and reproducibility) across a valid statistical population, quantity (5) of a given instrument/tool/system seems to be the "right" minimum number. I'm not certain of the origin of the analysis, but that seems to be the golden number, which may be why there were (5) built.

Regarding the original question, yes -- the "supreme master" gage block has been based on measurements of fundamental physical constants such as a wavelength of light. The hardware necessary for doing that isn't very portable. Anything that has a calibration traceable to NIST standards should be "pretty good", although the chain of traceability is sometimes longer than you might think. Any shop that has a set of gage blocks that are calibrated to 5-6 decimal places should be able to make and check parts like any other shop using the same standards and getting the same result, assuming of course that they actually are capable of using the tools properly and have a suitable environment.

 

[jccaclimber]

The meter has had different definitions over the years. There was a master chunk of metal (meter bar) until 1969. Now the definition is based off of light and a few other things. As usual the Wikipedia article sums it up half decently:

History of the metre - Wikipedia

en.m.wikipedia.org

Edit, for those working in freedom units, the inch is defined as a portion of a meter.

 

[turnworks]

Thank you all for the replies and links. That is more of a rabbit hole than I thought.

It all started when I was shopping for a new set of gauge blocks. I was confused about all the different grades and standards.

Thanks again.

 

[jccaclimber]

It hasn’t been mentioned, but unless you have really cheap gage blocks, you can't check them with a micrometer. A gage block at the edge of tolerance is still going to read as good on a micrometer unless you have one of the ones that reads in 0.1 um increments, and even then you're not going to be able to tell in many cases.

What you will be able to tell is if your blocks have a layer of goo on them or are warmed up by your hands, but at that point you're just doing a sanity check with a low accuracy device to validate a higher accuracy tool.

When I'm being lazy and to the nearest 0.001" or worse it's a $300 set from the net. I use them as precision shims occasionally as well, though not for a load bearing operation. Yes, really, that's why I actually got them.

When it's something I really care about the gloves come out and the $3k set of gage blocks get used. I do wish I'd have gotten the ceramic ones, simply to avoid corrosion issues and required oiling in my high humidity environment, but at the time it would have been doubling the price (ouch) and more importantly was something like a 12 week lead time because I use metric blocks, and that wasn't acceptable.