# Comparing Gage Block Sets



## Lucas E (Mar 3, 2021)

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.


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## T Bredehoft (Mar 3, 2021)

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.


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## macardoso (Mar 3, 2021)

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.
> 
> ...



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.


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## RJSakowski (Mar 3, 2021)

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.


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## JRaut (Mar 3, 2021)

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.


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## Winegrower (Mar 3, 2021)

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.


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## macardoso (Mar 3, 2021)

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!


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## RJSakowski (Mar 3, 2021)

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.


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## JRaut (Mar 3, 2021)

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.


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## RJSakowski (Mar 3, 2021)

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!


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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## Lucas E (Mar 3, 2021)

Winegrower said:


> 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.


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## projectnut (Mar 3, 2021)

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.
> 
> ...


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
					

Find many great new & used options and get the best deals for SHARS RECTANGULAR GAGE BLOCK SET 81 PC .05-4" AS-0 GRADE W/ NIST CERTIFICATE L} at the best online prices at eBay! Free shipping for many products!



					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.


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## macardoso (Mar 3, 2021)

RJSakowski said:


> 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.


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## Lucas E (Mar 3, 2021)

projectnut said:


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


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.


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## talvare (Mar 3, 2021)

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


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## Lucas E (Mar 3, 2021)

talvare said:


> 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!


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## Lucas E (Mar 3, 2021)

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.


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## Winegrower (Mar 3, 2021)

JRaut said:


> 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.


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## benmychree (Mar 3, 2021)

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".


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## mikey (Mar 3, 2021)

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.


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## Cadillac (Mar 3, 2021)

I would not trust any inspection sheet from China. All the ones I’ve ever seen are a xerox copy with a scribble. This is why a starrett or mitutoyo sets cost so much. All the sets I have are auction buys do-all, mitutoyo, and starrett. Inspections on three sets were in the late 80’s but I don’t care because I will NEVER be making stuff that requires that kind of accuracy. I maybe paid  50 bucks a set all the blocks ring even from different sets.
   I can’t see any hobbiest or a large percent of professional machine shops being able to measure to that tolerance let alone machine to that tolerance. Jmo


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## Dabbler (Mar 3, 2021)

Lucas I understand your desire for very accurate gauge blocs set, and if you can afford the best, then why not?  However as your OP implies being on a budget makes one open to cheaper alternatives...  I bought an offshore uncertified set about 35 years ago.  I have measured it in a lab against their best set using a half tenths indicator that could be read to about a third of that.  Only one block had any discernible deviation.

What I'm saying is that you get a lot for your money no matter what set you buy.

Now tracking requirement for precision:  are you machining to one thou precision, half thou or better?  My own personal opinion machining for 40+ years, and having firends in the trade much longer is this:

Develop skills and techniques like lapping, turning, finsihing and honing.  Use the best measuring tools you can afford.  With 25+ years experience, you will be able to reliably machine and finish to sub-thou.  Many home machinists fool themselves into thinking they can do better.

Even on the best surface grinders, for instance, it takes years to become a grinder hand and grind to 2 tenths overall and square.  The best a beginner can hope for is around 5 tenths on a new, tight machine, properly dressed wheel proper hardness and grit with perfect cooling.

The Shars sale one will do you for many years.  If you develop the skills to even measure to better tolerances, you will have hundreds of thousands of dollars invested, and buying a better set will be a drop in the bucket.

*This is one time 'buy cry once' doesn't work.  Buy a Shars set and use, abuse and wear it until you have the habits to care for a good set.  The cheap set becomes your setup and shop set, and your good set is used only for specific operations.  All really good tool and die shope used to follow this principle.*

My mentor had the skills to machine, heat treat, and grind inserts for punch presses.  He could stack 20 of them in a stack and measure the the whole tolerance was less than 2 tenths.  it took him 10 years to get it that good, with 20 years already under his belt.  This is the advice he gave me when I bought my first set.


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## DavidR8 (Mar 3, 2021)

^^^ is excellent advice!


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## mikey (Mar 3, 2021)

This whole thing is about trust ...


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## T Bredehoft (Mar 5, 2021)

I have a 20" gage block.  Its a Webber block, made by LSS. Co. It was scrapped by the U S Government (really) in the 1970's. In the 1990's the company I worked for  purchased measuring instruments that would allow me to check out my 20" gage block. At that time it's length was 20.0008. 
Apparently steel is not stable. I use gage blocks in set up, but don't rely on them for 100% accuracy.


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## erikmannie (Mar 5, 2021)

I bought the Shars metric as well as Imperial gage block sets. I was disappointed with the accuracy and consistency of both sets. I have a lot of Shars metrology products, and I generally find these to be a waste of money.

Shars is good for some purposes, but accuracy and consistency are not among them. If you were buying metrology products for a school or occasional casual use, Shars is a good choice. Shars products look good in photos, are very affordable, and they have very fast shipping. Their analog 0-1” screw thread micrometer has never let me down.


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## JRaut (Mar 5, 2021)

Hey @erikmannie, I generally like Shars for a lot of things as well, but I don't have any of their metrology stuff. I've got mostly vintage Starrett and Mitutoyo.

Care to elaborate on the accuracy issues with the gage blocks?

How far off were they from the stated tolerance?

And how did you measure?


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## erikmannie (Mar 5, 2021)

JRaut said:


> Hey @erikmannie, I generally like Shars for a lot of things as well, but I don't have any of their metrology stuff. I've got mostly vintage Starrett and Mitutoyo.
> 
> Care to elaborate on the accuracy issues with the gage blocks?
> 
> ...



When I first received the gage block sets, I only had Shars digital electronic mics and no mic stand. This went off the rails immediately as far as checking the gage blocks against the mics and vice versa.

Now I have Starrett mics and a mic stand. I have a week off now, so I will take a look at this right now using the Starrett mics and mic stand.

All of the coin batteries died in my Shars digital electronic micrometers, and when I put in new batteries all of them will now only read in mm.

Let me know what process you want me to undertake. In the meantime, I will check some random ones right now and post the results.


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## Janderso (Mar 5, 2021)

T Bredehoft said:


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


Interesting (off the subject) 
I'm working on my replacement. He is a perfectionist, an outstanding guy and he expects perfection from people.
I told him he is going to be disappointed. You can't expect perfection from imperfect people.
You try to bring out the best in those you have.
Sorry,
It was just an interesting comment as we were just discussing this.


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## JRaut (Mar 5, 2021)

erikmannie said:


> I bought the Shars metric as well as Imperial gage block sets. I was disappointed with the accuracy and consistency of both sets.



You say that you're disappointed with the accuracy and consistency of the gage block sets.

Just curious what you meant by that. How inaccurate are they? And how do you know?

I don't have a metric set, but would like one. So I'm shopping around.


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## erikmannie (Mar 5, 2021)

I cleaned the mic anvils + Starrett end measuring rod with acetone & used the wrench to get this right at 1.0000”. I’m using the tensioning knob. I will post pictures as this unfolds.

You guys may get some parallax, but this reads right at zero. I removed and replaced the standard two times, and it repeats.




Removing and replacing three times, the Shars 1.00000” gage block is always wider than the Starrett standard.




Removing and replacing two times, the Starrett standard always reads 1.0000”.




I would believe at this point that the Starrett standard and Shars gage block are not the same dimension.


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## erikmannie (Mar 5, 2021)

Here I have cleaned and adjusted so that the Starrett end measuring rod will repeatedly measure to be 4.0000”. I am making sure to be very consistent with the ratcheting tensioning knob.




The Shars gage blocking is a whopping 8 tenths longer than the Starrett standard.

It was too heavy to stay in the stand for the photo.


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## erikmannie (Mar 5, 2021)

I measured the Starrett 4” standard three times afterwards, and it is always right there.




It is 61°F where I am working, by the way.

I would conclude from this that the Starrett end measuring rod and Shars 4” gage block are not the same length.


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## erikmannie (Mar 5, 2021)

JRaut said:


> You say that you're disappointed with the accuracy and consistency of the gage block sets.
> 
> Just curious what you meant by that. How inaccurate are they? And how do you know?
> 
> I don't have a metric set, but would like one. So I'm shopping around.



Buy my metric set. I have yet to see a reason to take it seriously.


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## Dabbler (Mar 5, 2021)

@erikmannie What I see is what I'd expect.  Measuring using the standard isn't going to give you premium results but it is what you have.  for the 1" where the set shows it +11, that is +11 ten thousandths or +1 tenth.  That is what I'm reading on your mic.

It is better to calibrate them on a AA grade surface plate using a half-tenths indicator, comparing it to a master gauge block set.  I am suspicious of your 4" results, and would recommend checking both your standard and your mic against an outside standard, such as a B grade Mitutoyo gauge block, or better. I was lucky over the years to have access to lab quality surface plate and blocks.  This is no longer the case.

It probably is the case that the Shars calibration is lying, but it would be prudent to check first.  Cheap mic standards are notoriously fickle.


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## extropic (Mar 5, 2021)

My primary concern with inexpensive gage block sets is durability.
A buddy of mine had a set and, even though I was very careful, I managed to scratch one of the blocks.
I replaced that block with a Mitutoyo.
I don't trust off-brand gage blocks.


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## erikmannie (Mar 5, 2021)

Dabbler said:


> @erikmannie What I see is what I'd expect.  Measuring using the standard isn't going to give you premium results but it is what you have.  for the 1" where the set shows it +11, that is +11 ten thousandths or +1 tenth.  That is what I'm reading on your mic.
> 
> It is better to calibrate them on a AA grade surface plate using a half-tenths indicator, comparing it to a master gauge block set.  I am suspicious of your 4" results, and would recommend checking both your standard and your mic against an outside standard, such as a B grade Mitutoyo gauge block, or better. I was lucky over the years to have access to lab quality surface plate and blocks.  This is no longer the case.
> 
> It probably is the case that the Shars calibration is lying, but it would be prudent to check first.  Cheap mic standards are notoriously fickle.



As far as I know, the Starrett end measuring rods could be off. I was trying to do the best I could do with what I have to compare apples to apples.


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## extropic (Mar 5, 2021)

erikmannie said:


> As far as I know, the Starrett end measuring rods could be off. I was trying to do the best I could do with what I have to compare apples to apples.


 Just out of curiosity, after you used the 1" standard to "calibrate" your micrometer, did the mic read Zero when fully closed?


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## erikmannie (Mar 5, 2021)

extropic said:


> Just out of curiosity, after you used the 1" standard to "calibrate" your micrometer, did the mic read Zero when fully closed?



I did not check that.


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## erikmannie (Mar 5, 2021)

Here is the same thing with some metric items. I will change the methodology a little bit, and I will set the zero with the Shars gage blocks, starting with 50 mm.


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## erikmannie (Mar 5, 2021)

A Starrett 50 mm standard is the same. I’m not posting any pictures unless I found the measurements to be repeatable.


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## erikmannie (Mar 5, 2021)

Here is a 100mm Shars gage block in a Starrett 100-125 mm outside mic:


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## erikmannie (Mar 5, 2021)

The Moore & Wright standard measures 99.99 mm (.01 mm is about .0004”).


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## erikmannie (Mar 5, 2021)

After all of this, the mic measures the Shars 100 mm gage block to be 100.00 mm.


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## erikmannie (Mar 5, 2021)

The factory says that the 100 mm gage block is a little short (-.10 but I don’t know the units). Does anybody know what the units are for these deviation values? It would be a really tight tolerance if these were microns (1 micron = .000001 m = .001 mm).




Edit: the deviation values are given in microns.


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## macardoso (Mar 5, 2021)

I do wonder what it would cost to have the gage blocks calibrated by a NIST traceable lab. It would need to be a fraction of the price of a new set, otherwise nobody would ever calibrate and only buy new. Most shops calibrate all tools yearly.

I might have our guy at work get a quote for a few shop tools I have.


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## erikmannie (Mar 5, 2021)

Dabbler said:


> @erikmannie What I see is what I'd expect.  Measuring using the standard isn't going to give you premium results but it is what you have.  for the 1" where the set shows it +11, that is +11 ten thousandths or +1 tenth.  That is what I'm reading on your mic.
> 
> It is better to calibrate them on a AA grade surface plate using a half-tenths indicator, comparing it to a master gauge block set.  I am suspicious of your 4" results, and would recommend checking both your standard and your mic against an outside standard, such as a B grade Mitutoyo gauge block, or better. I was lucky over the years to have access to lab quality surface plate and blocks.  This is no longer the case.
> 
> It probably is the case that the Shars calibration is lying, but it would be prudent to check first.  Cheap mic standards are notoriously fickle.



Can you clarify “+11 ten thousands or +1 tenth”? I wonder if you mean “+11 hundred thousandths” (.00011”).

I had thought that these deviation values were in millionths of an inch. E.g., they say that the 1” gage block is actually 1.000011”.


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## extropic (Mar 5, 2021)

I haven't read the calibration standard document in more than 20 years, however I'm sure the "DEV" (deviation) value for an inch gage block is millionths (0.00000X) of an inch.


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## erikmannie (Mar 5, 2021)

Fascinating reading?



			https://www.nist.gov/system/files/documents/calibrations/mono180.pdf
		


Sample screenshot:


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## erikmannie (Mar 5, 2021)

macardoso said:


> I do wonder what it would cost to have the gage blocks calibrated by a NIST traceable lab. It would need to be a fraction of the price of a new set, otherwise nobody would ever calibrate and only buy new. Most shops calibrate all tools yearly.
> 
> I might have our guy at work get a quote for a few shop tools I have.



This price list says $3.20 to $5.70 for each gage block:


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## Dabbler (Mar 6, 2021)

I thought my offshore set was rated in microinches, but that wasn't the case.  It was rated in hundredthousandths not millionths. 

I think the economy sets are shown in tenthousandths not hundredthousandths, and your measurements seemed to bear that out.  All of mine measured within the tolerances stated in my test report, in hundrethousandths of an inch, as best as we could measure using a third of the marked indications on a half tenth indicator, comparing to a AA grade Mitutoyo gauge block set on a Mit AA grade surface plat in a climate controlled metrology room.

For a hobbyist, and 170 kanuckistan pesos [ > 15 years ago], It will do me just fine.  My worst block is just under a half a tenth out.  I'm very happy with my set.  If i work to half tenth tolerance one day I'll crow about it here!

EDIT:  The surprising thing here isn't that they are very good (which they are), but that they actually tested them at all!


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## erikmannie (Mar 6, 2021)

Dabbler said:


> I thought my offshore set was rated in microinches, but that wasn't the case.  It was rated in hundredthousandths not millionths.
> 
> I think the economy sets are shown in tenthousandths not hundredthousandths, and your measurements seemed to bear that out.  All of mine measured within the tolerances stated in my test report, in hundrethousandths of an inch, as best as we could measure using a third of the marked indications on a half tenth indicator, comparing to a AA grade Mitutoyo gauge block set on a Mit AA grade surface plat in a climate controlled metrology room.
> 
> ...



The Shars sets are good enough for what I do: 100% hobby stuff & NO customers (paid or otherwise) so that I can just follow my curiosity.

I would like to see somebody send a Shars gage block set to be calibrated, and then post the results.


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## Winegrower (Mar 6, 2021)

I just got a 81 piece HFS set, less than $100.   It includes the calibration chart, each block has a serial number and the nominal deviation in microinches.   As I read it, the ASME spec says the lowest grade is “Toolroom”, plus or minus 50 millionths, and all blocks in the set are below that, the worst being +32.   

One picky point is that 70% of the blocks are + tolerances.  Biased that way for wear?  Or just luck of the draw?

It would seem that a cheap set with a table of deviations from nominal in microinches would allow knowing the height of a stack to a few microinches, even if it was not some preset number.    Kinda fun, and impress your friends.


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## Liljoebrshooter (Mar 6, 2021)

Why not just send one or 2 blocks out and have them checked?  I looked at the prices awhile back and think it was like $6 each to have a block checked.   Mics were less than $20 for small ones. 
If you are trying to measure in microns and are fretting over a couple hundred bucks that is just silly.
Joe


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## Dabbler (Mar 6, 2021)

Liljoebrshooter said:


> Why not just send one or 2 blocks out and have them checked?




@Liljoebrshooter The places in Canada have a $150 minimum for certification, but it would be worth an ask.


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## Dabbler (Mar 6, 2021)

One of these days I'll find an inspection stand for my Mahr 2 millionths indicator so I can calibrate blocks myself.  If anyone sees one that is inexpensive, please PM me!


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