What's new
What's new

Are ring gages bored to a be within a certain tolerance or are they measured after?

FrodoLoggins

Plastic
Joined
Nov 10, 2019
I need a ring gauge, doesn't have to be a specific size I just need to know the exact size. So if I buy a 2" ring gage, I don't really care if it's exactly 2" or not, it can be 1.8293" as long as I know the exact bore diameter that's all I care about.

Now let's say I'm buying a 2" ring gauge. Is this gage going to be 2" plus or minus a certain tolerance? Or is it bored out to 2" plus/minus tolerance AND THEN inspected to get the exact diameter and labeled?

I'm assuming it's the latter, BUT I'm looking on MSC and the gages are specified as +/- .0001" or "Class L1". I'm assuming the exact diameter is within +/- .0001" of let's say 2" but are then inspected and labeled with the exact diameter such as 2.00001"?

EDIT: So for example here's a 1" ring gage (accurate to .0001"):
https://www.mscdirect.com/product/details/06543920?fromRR=Y

I'm assuming the bore could be anywhere from .9999" to 1.0001", but the exact diameter (let's say .99996") is measured and labeled as such. OR could the labeled ".99996" dimension actually be up to 1 tenth off?
 
I need a ring gauge, doesn't have to be a specific size I just need to know the exact size. So if I buy a 2" ring gage, I don't really care if it's exactly 2" or not, it can be 1.8293" as long as I know the exact bore diameter that's all I care about.

Now let's say I'm buying a 2" ring gauge. Is this gage going to be 2" plus or minus a certain tolerance? Or is it bored out to 2" plus/minus tolerance AND THEN inspected to get the exact diameter and labeled?

I'm assuming it's the latter, BUT I'm looking on MSC and the gages are specified as +/- .0001" or "Class L1". I'm assuming the exact diameter is within +/- .0001" of let's say 2" but are then inspected and labeled with the exact diameter such as 2.00001"?

EDIT: So for example here's a 1" ring gage (accurate to .0001"):
https://www.mscdirect.com/product/details/06543920?fromRR=Y

I'm assuming the bore could be anywhere from .9999" to 1.0001", but the exact diameter (let's say .99996") is measured and labeled as such. OR could the labeled ".99996" dimension actually be up to 1 tenth off?

I think they are inspected after and marked accordingly. Funny, we have a .99996" ring gage! :) Not bored though, ground and lapped and/or honed.....
 
Hi thanks. So just to clarify, if I just need to know the exact diameter but I don't care what that diameter is, gage class should be largely irrelevant to me, correct? A 2" ZZ class ring should be between 1.99968" and 2.00032" but the actual diameter labeled on the ring by the manufacturer should be basically as accurate as the device used to measure the ring, correct? It's not like it's labeled as 2.0000" but it's actually up to 2.00032"?
 
FrodoLoggins, that is my understanding. A ring gage should be marked with the actual size, as measured after production, not the nominal size. Tolerance is assumed to be +-1/2 of the least significant digit of the marking.

Keep in mind that if you pick up used ring gages that have been kicking around in tool cabinet drawers for unknown years, the current actual size (and cylindricality) may not be the same as when new.
 
I wouldn't expect a ring gage to have the actual size marked any more than I'd expect it on a gage block. The actual measurement should appear on the calibration certificate. AFAIK, rings are ground and lapped to be within their class and marked with the nominal, but customs will probably be different.
 
Interesting. I knew about x xx and z zz, but never knew there was a Y tolerance. Is that a special of sorts?

Couldn't tell ya. I have never ran across a Y tolerance either. I guess its for when a class Z just won't quite do, but you don't want to fork over X class dollars.
 
Hi thanks. So just to clarify, if I just need to know the exact diameter but I don't care what that diameter is, gage class should be largely irrelevant to me, correct? A 2" ZZ class ring should be between 1.99968" and 2.00032" but the actual diameter labeled on the ring by the manufacturer should be basically as accurate as the device used to measure the ring, correct? It's not like it's labeled as 2.0000" but it's actually up to 2.00032"?

All custom gages I have ordered had the size and class etched on them and then the cert stated the actual measurement. So if you order a 2" ZZ ring gage, it will be etched 2.000" ZZ on the ring gage. Then the cert will state the actual measurement.
 
I have a dozen ring gages used to set bore gages. Each is marked with a size of that ring. 0.7495 marked as example for the gage used with the .7500 - 1.000 bore gage. the step on the gage are .00025.
 
All custom gages I have ordered had the size and class etched on them and then the cert stated the actual measurement. So if you order a 2" ZZ ring gage, it will be etched 2.000" ZZ on the ring gage. Then the cert will state the actual measurement.

And any good cert will come with a guess range as to how accurate that "number" is to real.
 
Buy any brand ring gauge and send it for UKAS calibration( or your country equivalent). You will receive certificate showing size that was measured to a known uncertainty.
 
I wouldn't expect a ring gage to have the actual size marked any more than I'd expect it on a gage block. The actual measurement should appear on the calibration certificate. AFAIK, rings are ground and lapped to be within their class and marked with the nominal, but customs will probably be different.

Not so sure about that Conrad. All the "precision" ring gages I've encountered* are marked with actual size, on top of NIST specs.... I can see gage blocks, as it would be easier to include the cert with the deviance from nominal, as most sets are 81 pcs....

*used quite a few over the years for bearing bores and such
 
The way I see it, machined parts will always have a tolerance that is based off of the parts function. If it's a little too big or a little too small, it'll "work" as long as it's in tolerance and therefor the exact size is of little consequence. If it mattered, the part would be made to a higher tolerance.

Certification doesn't care so much about how the part is used, they measure a dimension with the highest accuracy they can and record the results. Any inaccuracy in that number has less to do with what's functional, and more to do with how reliable the measuring tools are. In other words, if your calibration is +/- .000005, that's not the same as a machining tolerance where as long as it falls in that range it's good. It means their tools are only going to give reliable measurements in that range. If the part was out of functional tolerance, it wouldn't be sold anyway.

So if measuring tool company A is making a ring gauge, that ring gauge part might have a tolerance of +/-.0001 or something when it's machined and ground to size, but then when it's certified, it'll get certified as .000056982 or something and that number will either be recorded on the gauge itself, or supplied on a certificate. IMO, the certificate is better as that number will change after it's had a million uses, and that's why you get it re-certified annually to determine what the new exact size is.
 








 
Back
Top