Mitutoyo setting ring accuracy.

ManualEd · Jan 14, 2017

Hey All,

Just looking at some Mitutoyo setting rings for some holtest mics, but I'm a bit stumped by the accuracy.

Setting Ring Series 177-Accessories for Inside Micrometers,Holtest and Dial Bore Gages

Edit edit: In the link above, the list of gages chart has an "Accuracy" column for any given gage size. The "accuracy" is listed as +- .00006 for ring gages up to 4".

±Tolerance between the nominal size and the actual diameter:
±0.01mm for ø1 - 45mm setting rings
±0.02mm for ø50 - 300mm setting rings
±.0004" for .1" - 1.8" DIA. setting rings
±.0008" for 2" - 12" DIA. setting rings

Is the tolerance between nominal and actual just saying that a 2" gage will be between 2.0008 and 1.9992, with a diameter accuracy of +-.00006 from marked size?

Edit: And is there a gage company that produces less expensive ring gages?
I don't care if my rings are all Mitutoyo, but I wouldn't mind having one ring sized for mid-travel of each head. Only one ring for each head can't tell you if its still accurate over the range or not.

The real Leigh · Jan 14, 2017

ManualEd said:
Is the tolerance between nominal and actual just saying that a 2" gage will be between 2.0008 and 1.9992, with a diameter accuracy of +-.00006 from marked size?

I don't understand where that .00006 number came from.

The actual diameter will be between 1.9992" and 2.0008".
That is the tolerance for manufacturing the physical gage.

The actual diameter of any given gage is engraved on the gage itself.
That dimension is usually presented to five or six decimal places.

- Leigh

ManualEd · Jan 14, 2017

The real Leigh said:
I don't understand where that .00006 number came from.

The actual diameter will be between 1.9992" and 2.0008".
That is the tolerance for manufacturing the physical gage.

The actual diameter of any given gage is engraved on the gage itself.
That dimension is usually presented to five or six decimal places.

- Leigh

In the link above, the list of gages chart has an "Accuracy" column for any given gage size. The "accuracy" is listed as +- .00006 for ring gages up to 4".

+-.0008 diameter tolerance for a 2"- 12" gages would be useless for most things.

The real Leigh · Jan 14, 2017

ManualEd said:
+-.0008 diameter tolerance for a 2"- 12" gages would be useless for most things.

It appears you don't understand how gages are made.

A gage is a piece of metal, just like any other piece of metal.

It's made on a machine that cuts it or grinds it to size.

The piece coming off that machine must be within the stated diametral tolerance.

Then it gets measured.
That measured dimension is accurate to the stated tolerance, 60 millionths or whatever.

So the real gage may be 1.9995" or 2.0003" or whatever.
That dimension is known within the stated measurement accuracy.

- Leigh

Gordon B. Clarke · Jan 14, 2017

ManualEd said:
In the link above, the list of gages chart has an "Accuracy" column for any given gage size. The "accuracy" is listed as +- .00006 for ring gages up to 4".

+-.0008 diameter tolerance for a 2"- 12" gages would be useless for most things.

Technical Data

±Tolerance between the nominal size and the actual diameter:
±0.01mm for ø1 - 45mm setting rings
±0.02mm for ø50 - 300mm setting rings
±.0004" for .1" - 1.8" DIA. setting rings
±.0008" for 2" - 12" DIA. setting rings

Cylindricity:

1.0μm for ø1 - 60mm setting rings
1.5μm for ø 62 - 90mm setting rings
2.0µm for ø 100 - 150mm setting rings
2.5µm for ø 175 - 225mm setting rings
3.0µm for ø 250 - 300mm setting rings
.00004˝ for .1˝ - 2.4˝ DIA. setting rings
.00006˝ for 2.5˝ - 3.6˝DIA. setting rings
.00008˝ for 4˝ - 6˝ DIA. setting rings
.00010˝ for 7˝ - 9" DIA. setting rings
.00012˝ for 10˝ - 12˝ DIA. setting rings

I suggest you focus on this part and read again what Leigh wrote in post #2

You have me wondering what you use a setting ring for.

Let's see if I can explain how a setting ring is made. A nominal diameter is selected. As nothing can be made exactly a tolerance is stipulated. Often a temperature is stipulated too. When the ring is finished it is then measured as exactly as possible and it is this measurement that is stipulated on the ring. The stipulated measurement of course has to be within the stipulated tolerance.

Edit: And is there a gage company that produces less expensive ring gages?
Of course there are. try Googling "setting rings gages"

I don't care if my rings are all Mitutoyo, but I wouldn't mind having one ring sized for mid-travel of each head. Only one ring for each head can't tell you if its still accurate over the range or not.
Simply buy two of different diameters within the range you want/need.

ManualEd · Jan 14, 2017

The real Leigh said:
It appears you don't understand how gages are made.

A gage is a piece of metal, just like any other piece of metal.

It's made on a machine that cuts it or grinds it to size.

The piece coming off that machine must be within the stated diametral tolerance.

Then it gets measured.
That measured dimension is accurate to the stated tolerance, 60 millionths or whatever.

- Leigh

I really didn't, but I have an idea now. Thank you!

My only experience with metrology is from what I read on this forum.

When they make a 2" setting ring, so long as they're within their +-.0008" from nominal, the main concerns are the cylindricity, and surface finish, so that they can make an accurate measurement of the ring?

ManualEd · Jan 14, 2017

Gordon B. Clarke said:
Technical Data

±Tolerance between the nominal size and the actual diameter:
±0.01mm for ø1 - 45mm setting rings
±0.02mm for ø50 - 300mm setting rings
±.0004" for .1" - 1.8" DIA. setting rings
±.0008" for 2" - 12" DIA. setting rings

Cylindricity:

1.0μm for ø1 - 60mm setting rings
1.5μm for ø 62 - 90mm setting rings
2.0µm for ø 100 - 150mm setting rings
2.5µm for ø 175 - 225mm setting rings
3.0µm for ø 250 - 300mm setting rings
.00004˝ for .1˝ - 2.4˝ DIA. setting rings
.00006˝ for 2.5˝ - 3.6˝DIA. setting rings
.00008˝ for 4˝ - 6˝ DIA. setting rings
.00010˝ for 7˝ - 9" DIA. setting rings
.00012˝ for 10˝ - 12˝ DIA. setting rings

I suggest you focus on this part and read again what Leigh wrote in post #2

You have me wondering what you use a setting ring for.

Let's see if I can explain how a setting ring is made. A nominal diameter is selected. As nothing can be made exactly a tolerance is stipulated. Often a temperature is stipulated too. When the ring is finished it is then measured as exactly as possible and it is this measurement that is stipulated on the ring. The stipulated measurement of course has to be within the stipulated tolerance.

I'm just using them for setting bore micrometers.
I confused the tolerance of the ring gage from nominal with the accuracy of it.

Gordon B. Clarke · Jan 14, 2017

ManualEd said:
I'm just using them for setting bore micrometers.
I confused the tolerance of the ring gage from nominal with the accuracy of it.

My compliments. Not all would admit what you've just written :cheers:

Now Leigh and I can sleep again at night

The real Leigh · Jan 14, 2017

Gordon B. Clarke said:
Now Leigh and I can sleep again at night

On different continents, thank you. :crazy:

- Leigh

DMF_TomB · Jan 14, 2017

most places have each ring gage measured every year and the error amount is listed on each ring gage
1.0000 +100
+100 is in millionths (normally error under 100)
so
1.000100" is actual size
.
you set indicating or tri mics gage using nominal value AND error amount. really bad condition gages can be chrome plated and reground. plenty of plain steel gages get rusty after decades. when you clean rust obviously you removing metal

ManualEd · Jan 14, 2017

DMF_TomB said:
most places have each ring gage measured every year and the error amount is listed on each ring gage
1.0000 +100
+100 is in millionths (normally error under 100)
so
1.000100" is actual size
.
you set indicating or tri mics gage using nominal value AND error amount. really bad condition gages can be chrome plated and reground. plenty of plain steel gages get rusty after decades. when you clean rust obviously you removing metal

Tom, what do you mean when you say you have to set the tri mic using nominal AND error amount?

DMF_TomB · Jan 14, 2017

ManualEd said:
Tom, what do you mean when you say you have to set the tri mic using nominal AND error amount?

.
.
if ring gage is
1.0000 +1000 (never that far off but for explaining example)
thats 1.0000 +.001000 = 1.0010" so you would set tri mics to read 1.0010"
.
many tri mics can come with handle extension so it is a longer length to reach in deeper bores. quite normal after extension installed or removed for calibration to easily change .001"
.
i always check tri mics with ring gage before use. you never can be sure if someone removed handle extension and did not reset tri mics. it usually just single set screw to loosen barrel and line up with proper mark and retighten set screw. takes maybe 1 minute
.
picture shows small to medium size parts (usually 1 ton or less) that often need longer gages to reach in to measure

ManualEd · Jan 14, 2017

DMF_TomB said:
.
.
if ring gage is
1.0000 +1000 (never that far off but for explaining example)
thats 1.0000 +.001000 = 1.0010" so you would set tri mics to read 1.0010"
.
many tri mics can come with handle extension so it is a longer length to reach in deeper bores. quite normal after extension installed or removed for calibration to easily change .001"
.
i always check tri mics with ring gage before use. you never can be sure if someone removed handle extension and did not reset tri mics. it usually just single set screw to loosen barrel and line up with proper mark and retighten set screw. takes maybe 1 minute
.
picture shows small to medium size parts (usually 1 ton or less) that often need longer gages to reach in to measure

A ring gage will usually be with a +- spec of the size written on the ring. Don't you just set it for what it says on the ring?

The real Leigh · Jan 14, 2017

ManualEd said:
A ring gage will usually be with a +- spec of the size written on the ring. Don't you just set it for what it says on the ring?

It depends on how the ring gage is marked.

If it shows a nominal value and an error term, you add those to get its true dimension.

It it has a dimension that was added after fabrication, commonly not equal to the nominal value, you use that as the true dimension.

- Leigh

ManualEd · Jan 14, 2017

The real Leigh said:
It depends on how the ring gage is marked.

If it shows a nominal value and an error term, you add those to get its true dimension.

It it has a dimension that was added after fabrication, commonly not equal to the nominal value, you use that as the true dimension.

- Leigh

I haven't come across any gages like that yet.

If it has the nominal value, and an error term, will that error term always be listed as a +.xxxx OR a -.XXXx? Not a +-.xxxx?

And what would be the reason for not marking it after fabrication with an actual dimension? Since you have to measure it, and mark it anyways?

Is that just the preference of the gage maker?

The real Leigh · Jan 14, 2017

An error term would always be marked with the correct sign, not with +-.

I have seen gages marked with the nominal dimension etched, and the error term added.

I don't know why that was done. They didn't solicit my advice.

I suspect "nominal with error" would be more common with gages in a set, so individual members would be identified without ambiguity.

Gages that are made to order or supplied singly would likely bear the true dimension.

- Leigh

Gordon B. Clarke · Jan 15, 2017

ManualEd said:
I haven't come across any gages like that yet.

If it has the nominal value, and an error term, will that error term always be listed as a +.xxxx OR a -.XXXx? Not a +-.xxxx?

And what would be the reason for not marking it after fabrication with an actual dimension? Since you have to measure it, and mark it anyways?

Is that just the preference of the gage maker?

When I send something out for calibration to an authorized lab the certificate states the measurement. What is added is "measurement uncertainty" and that is usually given as ± and to tenths of 1µm

The real Leigh · Jan 15, 2017

Gordon B. Clarke said:
What is added is "measurement uncertainty" and that is usually given as ± and to tenths of 1µm

We're confusing terms here.

Measurement uncertainty on a calibration certificate is any potential error in the instruments that are measuring the gage, not errors in the gage itself.

As I mentioned before, all measurements have inaccuracies that are a function of the instrument making the measurement.

This should not be confused with any deviation in the gage from its nominal value.

- Leigh

ManualEd · Jan 15, 2017

The real Leigh said:
We're confusing terms here.

Measurement uncertainty on a calibration certificate is any potential error in the instruments that are measuring the gage, not errors in the gage itself.

As I mentioned before, all measurements have inaccuracies that are a function of the instrument making the measurement.

This should not be confused with any deviation in the gage from its nominal value.

- Leigh

So how would the measurement uncertainty correlate to the accuracy of the measurement marked on the gage?

If you assume that the cylindricity and surface finish are perfect (not that it's possible), would the accuracy of the measurement on the gage be the measurement uncertainty? Or are there other factors that affect your measurement accuracy?

2.00000 +- some manner of the measurement uncertainty?

A little bit of a side question, of which my misunderstanding was the reason for starting this thread:
what's the proper way to refer to the accuracy of a ring gage?
It seems wrong to say that the accuracy of the ring gage is +-.XXXXX, because its the MEASUREMENT of the gage that is accurate to +-.XXXXX, not the ring gage itself.

The real Leigh · Jan 15, 2017

ManualEd said:
It seems wrong to say that the accuracy of the ring gage is +-.XXXXX, because its the MEASUREMENT of the gage that is accurate to +-.XXXXX, not the ring gage itself.

You really need to study the subject of metrology and he hierarchy of accuracies to understand this. There are numerous books on the subject.

And that's my point. Books have been written on this subject.
It's not something that can be covered adequately in a thread on an internet forum.

This is turning into a circular question, which I will close.

- Leigh

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