Micrometer standards are not very accurate?

I needed to set zero on a new Starrett 10ths reading 3" to 4" micrometer. So I use the supplied standard. I was called away for a few minutes and forgot I had set zero and got another standard that was closer to me (Brown & Sharpe, USA made) and it reads .0002" bigger. I rechecked with the Starrett and it was definitely smaller. So I get a no-name China standard it's also a different length. Finally I used a gauge block and its a little bit smaller than them all.

Now I don't trust the standards at all. So now I have a new $250 micrometer with a standard that may or may not be 3"

The Brown & Sharpe just says 3 on it. Same for the Chine one.

The Starrett standard says nothing.

Mitutoyo says a 3" standard is only accurate to +/- .0001" and one made in China, who knows?

Mitutoyo says the bigger sizes can be +/- .0003" to .0004"

Is everyone else using gauge blocks. I have micrometers that go up to 14" and don't have gauge blocks that big.

I thought standards were made to a nice round number. But, after being made and ground then they are measured and the actual length is marked on it. Like a 1" standard may be marked 1.001". The Harbor Freight stuff is just marked with a nice round number with no measuring.
Bill D

Laverda said:

....

Now I don't trust the standards at all.

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Love this, now is this your standards or your capability to master to one made a tad different?
Who is in error? Are gauge blocks a better master?
Who and what to trust.
Bob

French proverb: If someone has a watch, everyone knows what time it is. If three people have a watch, nobody knows what time it is.

So those standards come with the micrometer, included with the price. An individual, 3", grade 0 Jo block can cost close to $70. Or more.

What do you expect? The micrometer manufacturers state the accuracy of their micrometers but I have not ever seen any statement of the accuracy of the included standards.

I have a question. Just how much attention did you pay to the temperature of the various standards, Jo blocks, and micrometers while you were comparing the standards? The temperature coefficient for steel is around 11 or 12 X 10^-6 per degree C. For a three inch, steel standard that becomes 0.000033" to 0.000036" per degree C. And a 3 degree C (5.4 degree F) difference will produce a change around 0.0001".

So I ask were you careful to be sure to allow some time (5 or 10 minutes or more) for both the micrometers and the standards to come to the same temperature? Did you handle the micrometer only by the insulating pads? And only handle it as little as possible? Even plastic can transmit heat and it will take a longer time to equalize to room temperature after handling so holding it by those insulating pads can throw it off for a longer time than handling one by the metal frame. Did the standards even have any thermal insulation? Jo blocks do not have any insulation so they must be allowed to come back to the same temperature after handling. Etc.

The failure to take temperature into account can easily account for the differences you talk about. This is one very good reason for using one of those mike stands.

Starrett and Mitutoyo standards have never concerned me much especially if I use those as Mics also. Sure there are others I would trust. Too it never hurts to verify standards of both to the micrometers and even compare others to come to conclusions about accuracy if one must.

Personally I trust both of those brands and I had to choose only one which I could use it would be Mitutoyo. I hate saying that but it is true for me. Gage pins and gage blocks will vary upon grade and the more accurate the more expensive. Notice gage pins come plus minus and they will be dead accurate.

If you check them with a off brand Micrometers then all I will say is it is better to use top quality and proven brands if one is serious about validity. I have been told I am wrong about that yet I do very well with what I make because I check them my way and trained by the old timers. It has been the case that those who said such things usually move on as they have other quirks that move them elsewhere with their brand of expertise. It is not the only way people do things but is is how I do it unless ordered to do things differently.

Then under that circumstance it is out of my control as it is the owners decision and perhaps his selected and calibrated tools. I will point out that everything is calibrated officially and certified and tagged. Even so I have seen outfits who do that and they are on the cheap-not my choice or selection.

I will protest that though. Once you deal with the sum of one’s trained and active experience you can tell the difference with companies who come in and calibrate.

What k9nds of verifications are actually implemented and followed plus documented and enforced tells on a lot about the professionalism and care of any shop. Hands down. iMO

The other thing is the ends of the standard.... Flat ones have one dimension, rounded ones might have many. Maybe the rounded ones are supposed to be made rounded to a diameter corresponding to the length, but I don't think that all are.

Flat ones you have to get flat on the anvils of the mic, or they read large. But they are clumsy to use, and often are a smaller diameter of flat spot than the mic anvils. Easier to get it flat on a stack of gauge blocks.

If you have the blocks, don't screw with the standards

I long ago came to the conclusion that most people who talk tenths are crazy. One ten-thusandth of an inch is a very small amount, and not that easy to measure accurately. Then even if you can, that doesn't mean it will be when it leaves the totally-controlled environment necessary to measure, and enters the real world.

Laverda said:

I needed to set zero on a new Starrett 10ths reading 3" to 4" micrometer. So I use the supplied standard. I was called away for a few minutes and forgot I had set zero and got another standard that was closer to me (Brown & Sharpe, USA made) and it reads .0002" bigger. I rechecked with the Starrett and it was definitely smaller. So I get a no-name China standard it's also a different length. Finally I used a gauge block and its a little bit smaller than them all.

Now I don't trust the standards at all. So now I have a new $250 micrometer with a standard that may or may not be 3"

The Brown & Sharpe just says 3 on it. Same for the Chine one.

The Starrett standard says nothing.

Mitutoyo says a 3" standard is only accurate to +/- .0001" and one made in China, who knows?

Mitutoyo says the bigger sizes can be +/- .0003" to .0004"

Is everyone else using gauge blocks. I have micrometers that go up to 14" and don't have gauge blocks that big.

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One has "standards" calibrated and MARKED if/as/when you actually NEED that.

And "not often".... as the typical micrometer is easily as sensitive to the QC repeatabilty standard of the nut holding it off the deck.

The user, IOW.

Especially the "apprentice" mics. Starrett, for example.


No calibration label. No trust.

Can't remember if you walked to work, packed a bag lunch, took a dump, or rode a dragon-lizard downhill, side-saddle, at the gallop?

That won't fly well nor long in a(ny) machine shop. Can't solve a problem nor compete a task if you can't remeber it .


Gage block sets have "extensions". My ones total to ninety inches. IF one were to put them end-to-end. Which you do esseantailly never.

Pick up one or two extensions PLUS the sets of goods made to hold a stack to make it easier to manipulate.

THEN your large mic issue is solved at MULTIPLE checkpoints - chosen to be closer to the critical need, not just the one length a standard covers.

That's why I have both. And more.

They, too, will need to be calibrated and recorded or labeled. If you need that.

I find it MUCH cheaper to just not kid myself so dam' often.

Human's don't "doo" uber-fine work casually on a whim.

They need to focus the mind, sensitize eye/brain, nerve, & muscle, "get into the groove" or "mode" in order to do their best at it.

Not all have the paitience or understanding to JFDI. Buying tools is only the half of it.

EVERYTHING moves. Not just in a shop.

In the entire freakin' universe.

Get used to it.

As EPAIII said I think it is the temperature. Measure again tomorrow and they'll all be different again. Try wearing gloves.

McMaster lists the accuracy of the Starrett end measuring rods as "0 to 0.0001" (up to 6").

EmanuelGoldstein said:

I long ago came to the conclusion that most people who talk tenths are crazy. One ten-thusandth of an inch is a very small amount, and not that easy to measure accurately. Then even if you can, that doesn't mean it will be when it leaves the totally-controlled environment necessary to measure, and enters the real world.

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WTF would a Kommie-sock-puppet KNOW about "real world?"

Folk who need to work "tenths" do so. Or millionths.

ELSE NOT!

EmanuelGoldstein said:

I long ago came to the conclusion that most people who talk tenths are crazy. One ten-thusandth of an inch is a very small amount, and not that easy to measure accurately. Then even if you can, that doesn't mean it will be when it leaves the totally-controlled environment necessary to measure, and enters the real world.

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and i came to the conclusion a long time ago that most people who work with and to tenths for the most part have no hair left on there head . val would say plus or minus one bus stop

EmanuelGoldstein said:

that doesn't mean it will be when it leaves the totally-controlled environment necessary to measure, and enters the real world.

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And suddenly it becomes clear what the attraction is for totalitarian-loving communists - they want total control so they can ensure their micrometers measure to the micron!

Now I get it - Xi and Putin aren't bent on world domination. They're just frustrated mechanical inspectors acting-out...

1yesca said:

and i came to the conclusion a long time ago that most people who work with and to tenths for the most part have no hair left on there head . val would say plus or minus one bus stop

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Wise women will even tell you WHY.

Hair never stops growing on the male.

It simply reverses direction.

Grows inward

... until it has filled the skull, displaced the last of the brain tissue towards the glans of the penis, and stray hairs escape to appear out the nose and ears.

The surplus of brains in the penis then cause a malfucktion.

It was never designed for HEAVY thinking!

No reasonable person uses standard micrometers to measure to a tenth. Pick a better yardstick.

EmanuelGoldstein said:

I long ago came to the conclusion that most people who talk tenths are crazy. One ten-thusandth of an inch is a very small amount, and not that easy to measure accurately. Then even if you can, that doesn't mean it will be when it leaves the totally-controlled environment necessary to measure, and enters the real world.

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Ha Ha Goldstien! you are doing just what you should be, holding your pants up! What a bum you are, in the real world! How about some photos out of you! Ha Ha!!

It is very easy to talk about holding a tenth with a regular vernier mic. Not so easy in practice. A small temperature difference unaccounted for can throw that out the window. Same with an inaccurate standard check of the mic, or even measuring a surface that doesn't have the same texture or shape as the standard. The pressure of the micrometer spindle becomes critical at that level. Best to use an indicating micrometer or comparator at that level. That's not to say it can't be done, but it requires a lot of care and checking that measurements between a micrometer and a gage block stack with an indicator as a comparator are the same. They often will not be, due to whatever is causing the error in that particular setup. It's a lot easier on small stuff since temperature doesn't affect it as much.

Regarding the standards, if you are trying to check them to the tenths level you should be sending them out for calibration, or if you have the capability, checking them against a known good (again, calibrated) gage block. It is not uncommon for the standards to vary a tenth or two, and old ones with the radius formed ends can wear easily - they only make point contact with the micrometer.

thermite said:

Wise women will even tell you WHY.

Hair never stops growing on the male.

It simply reverses direction.

Grows inward

... until it has filled the skull, displaced the last of the brain tissue towards the glans of the penis, and stray hairs escape to appear out the nose and ears.

The surplus of brains in the penis then cause a malfucktion.

It was never designed for HEAVY thinking!

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so its not because of to meany u turns under the sheets

Red James said:

No reasonable person uses standard micrometers to measure to a tenth. Pick a better yardstick.

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That's easy to say, but on the bench in the real world you have to work with what's available. And make it work. Years back I was the sole shift operator on the jig grinder. One job that came up regularly was to ID grind hardened steel rings that would be a shrink fit for carbide slugs. This was 1" diameter and the shrink allowance and tolerance was in tenths. The available tools were the parts to fit, my micrometers and telescoping gauges. Don't tell me it can't be done, because we did it routinely. Doing it successfully was a matter of process and sensitivity to "feel" and I was fortunate in having a good mentor.

I moved to another job in the factory and another guy took my place who happened to have a higher class than I'd had, but that was more a matter or seniority than skill. In any case, one of the other guys told me later with some amusement that the first time this guy did the job, he ground the rings, heated them in the oven, slipped the carbide slugs in and let the whole shebang cool just as the process required. When they were picked up the slugs fell right out. If you don't use the right procedure and pay infinite attention to feel it doesn't work.

laverda, how many measurements did you take per piece? if measuring to a few µ you better be sure the mikes surfaces are flat (→optical flat). you have to clean them in exactly the same manner. i gave up on absolute measurement of this kind a while ago. and with a vernier type no way.