Comparing Gage Block Sets

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Lucas E

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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.
 
If you strive for perfection you will be dissatisfied with everything you do and will soon look for other avenues to perfection. Good luck.

I'm human, I can't make perfect things, I'm happy to be able to come close. .001 is acceptable, .0005 is luck, .0001 is beyond my abilities.
 
Lucas E said:
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.
Click to expand...

To me, if they have calibration certificates, then I trust the numbers. Shars has been good to me over the years and I think they represent the middle end of the import market. You are paying $$ for the Starrett or Mitutoyo name.
 
Any set of gage blocks can be calibrated for NIST certification. Probably of concern should be the quality of the machining. do the surfaces permirt wringing, how parallel are the surfaces. NIST calibrations should furnish a deviation from nominal dimension for each block. and assuming the maching is adequate, a cheap set will be just as functional as a high end set.
 
Just curious:

What are you working on that you need such precision?

I use a set of Mitutoyo blocks that were last calibrated in the 80s or 90s. No idea if they're still in spec. But they're plenty good enough for me if they're within a tenth.

The tolerances you're talking about are more than an order of magnitude tighter than a tenth. What measurement tools do you have that make use of that tight of tolerances; run-of-the mill micrometers and the like are in a completely different ballpark.
 
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.
 
While reading Foundations of Mechanical Accuracy, I noticed they were concerned about the thickness of the wringing film. That is only about 1/4 of a millionth of an inch - nuts!
 
The issue is tolerance stacking. If you stack five blocks to make a dimension, the tolerance has potentially decreased b an order of five.

Personally, my philosophy is that if care is taken, there is no reason why something like a gage block shoulde go out of tolerance. If is different if one is using them on a regular basis for setups. The last shop that I was involved with had a junker set for general shop use and a Q.C. set reserved for calibration.
 
I believe the tolerances referenced by the OP are in microinches, not microns (micro-meters).

Correct me if I'm wrong, of course. I'm basing that on some tolerance literature I found online.

So the stack-up in your example would be out only 11 microinches.
 
macardoso said:
While reading Foundations of Mechanical Accuracy, I noticed they were concerned about the thickness of the wringing film. That is only about 1/4 of a millionth of an inch - nuts!
Click to expand...
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.
 
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