Comparing Gage Block Sets

[Lucas E]

My Mitutoyo digital mic, which is the most accurate and precise instrument I have, only resolves to 50 microinches. A micron is about 39 microinches. Let’s say you stack four gauge blocks, two in the 6 micron tolerance range and two in the 5 micron region. These tolerances don’t add linearly but add up as the square root of the sum of the squares. So the expected tolerance of the stack would be 11 microns, or 430 microinches, or about 4 tenths. This is easily discernable.

Only you know if this is acceptable.

Excellent example. You cannot qualify a measuring tool to .0001 using gage blocks that have a +-.00005" tolerance. Although I think Jrout is right that it's only 11 microinches. Stacking all the tolerances would be out 22 microinches, however using the squareroot of the sum of the squares that brings it down to 11 microinches since some of the tolerances should average out as opposed to the all being at the max and stacking.

Using the 4:1 rule. That should allow the blocks to calibrate to .000044" (~50 millionths) in that size range. Which is what a mitutoyo digital mic reads out to.

 

[projectnut]

I'm in the market for a gage block set that I plan to use to calibrate my measuring tools and use as a calibrated shop reference. Therefore I'm only considering NIST traceable so I know my masters are verified against a universal standard. I'm looking at the SHARS grade AS-0 SKU: 303-5307C set that is NIST traceable with serial numbers. It's specs are 5µ (0.05-0.4"), 6µ (0.45-1"), 8µ (2"), 10µ (3"), 12µ (4").

At $415 I'm skeptical since the equivalent grade 0 Mitutoyo or Starrett are around $1600. However it does state they are measured according to ASME B89.1.9-2002 and each block is serialized and the deviation from the NIST traceable size is recorded.

Does anyone have any experience having a set like this independently qualified and verified their stated accuracy isn't bogus?
Am I wasting my time/money even considering something that is this cheap? Is there another brand I should be considering?

There is a Starrett Grade B 81 piece set for only 500, but the grade B specs aren't tight enough tolerance for what I want.

Shars has the same set available through their eBay store (Discount Machine) for $269.00 plus $22.00 shipping.

SHARS RECTANGULAR GAGE BLOCK SET 81 PC .05-4" AS-0 GRADE W/ NIST CERTIFICATE L} | eBay

The mirror finished surface allow the gage block to be easily wringable. Each block is wrapped in a greasproof paper and placed inside the plastic insert holder to prevent corrosion and abrasion. at Fixed Prices.

www.ebay.com

As for being certified it's somewhat of a misnomer. All their products are guaranteed to meet the published specs. If they don't they can be returned. There is a substantial difference between a certified set and a non- certified set. If you read the certification certificate closely all it guarantees is that the blocks will meet the stated spec. If they don't they will be replaced on an individual basis.

I posed a similar question about gauge pins on another professional board. The overwhelming opinion was not to pay for certification unless you are doing work for a company that is ISO certified and needs all their vendors to also be ISO certified. In over a dozen responses none had purchased certified pins due to the difference in cost and lack of recourse should the pins not meet specifications.

I've had the gauge pins a couple months and so far every one I've used is within .0001" which is as small as I can measure.

 

[macardoso]

Tom Lipton did an interesting experiment to see if the thickness of a Sharpie mark would affect a measurement. As I recall, it didn't.

All depends on how tight you need to measure to! Those guys at Moore were doing some incredible work.

 

[Lucas E]

Shars has the same set available through their eBay store (Discount Machine) for $269.00 plus $22.00 shipping.

SHARS RECTANGULAR GAGE BLOCK SET 81 PC .05-4" AS-0 GRADE W/ NIST CERTIFICATE L} | eBay

The mirror finished surface allow the gage block to be easily wringable. Each block is wrapped in a greasproof paper and placed inside the plastic insert holder to prevent corrosion and abrasion. at Fixed Prices.

www.ebay.com

As for being certified it's somewhat of a misnomer. All their products are guaranteed to meet the published specs. If they don't they can be returned. There is a substantial difference between a certified set and a non- certified set. If you read the certification certificate closely all it guarantees is that the blocks will meet the stated spec. If they don't they will be replaced on an individual basis.

I posed a similar question about gauge pins on another professional board. The overwhelming opinion was not to pay for certification unless you are doing work for a company that is ISO certified and needs all their vendors to also be ISO certified. In over a dozen responses none had purchased certified pins due to the difference in cost and lack of recourse should the pins not meet specifications.

I've had the gauge pins a couple months and so far every one I've used is within .0001" which is as small as I can measure.

Thank you for pointing that out. I will make sure to order from there if i do. However, now i'm extra leary of the specs.

The problem is, i don't have any way to verify if their specs are correct or not. I don't have any NIST traceable standards to compare them against, nor the equipment to measure that tight.That's why i need to trust that what i'm getting is in the right spec. It's worth it to me to pay for the NIST traceable, that way i know the extra effort has gone in to verify they are what they say they are.

 

[talvare]

I would think that when you are working to these kind of tolerances, ambient temperature would come into play. So, unless you are taking measurements in a temperature controlled environment, I'm not sure you could trust those measurements down to the micron. Just my two cents.
Ted

 

[Lucas E]

I would think that when you are working to these kind of tolerances, ambient temperature would come into play. So, unless you are taking measurements in a temperature controlled environment, I'm not sure you could trust those measurements down to the micron. Just my two cents.
Ted

It's not so much about working to microinches. It's that the blocks need to be an order of magnitude more accurate than the tools they are calibrating. Also, 68 degrees is the standard temperature. My measuring/calibrating will be done inside a temp controlled room. Although I wish they would have made the standard 70 as I find that more comfortable ha!

 

[Lucas E]

Another thing i don't like is they seem to have conflicting tolerances on their website and ebay page. They say their accuracy is +.000004 -.000002.



But then in the chart below states through 1" are +-6 which is really .000012.


That would make a stack of 4 be double, or 22 microinches. 4:1 rule would put that at .000088" which is more than a mitutoyo digital mic reads out at. I understand its splitting hairs (or fractions of a hair!) however the inaccuracies in their claims makes me not believe them. However i want to understand more before paying 6 times as much for something i feel i could trust.

 

[Winegrower]

I believe the tolerances referenced by the OP are in microinches, not microns (micro-meters).

Thank you, I was incorrect to assume the OP use of the Greek mu implied microns. It should have been modified by the units, microns or microinches.

Sorry. 11 microinches! That suggests these blocks are pretty good reference standards, especially for hobby use.

 

[benmychree]

Worrying about using gage blocks in a home shop situation is ludicrous, without controlled temperature, that sort of precision is impossible, and with the sort of machinery that nearly all home shops have, achieving a workpiece of that sort of precision is impossible, as a German guy that I knew would say "Zis is garbage, crazy in za first place and schtupid to end with".

 

[mikey]

Lucas, I own a grade B steel set from a German metrology lab that is accurate to 0.00005". I also own a Mitutoyo grade 0 Cerastone set (NIST-certified) intended for micrometer calibration in a lab. Using a Mitutoyo Quantumike accurate to 0.00005", I can measure no difference between the two sets.

Like you, I wanted to be able to trust my tools to actually read what they are supposed to read, which is what prompted me to buy the Mitutoyo set. I wrote up my test here. Knowing what I know now, I suggest you buy a decent grade B set from Shars without the certification. Buy it new and trust it; it will be good enough for use in your hobby shop. The only reason to buy a NIST-certified set is to be able to show that the tools used for a job met the NIST requirement; this would only happen in a job shop that took on work that required this sort of thing.