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tmc_31
08-21-2009, 08:49 PM
Hey guys,

I have been reading about gage blocks. My understanding is that they are a standard reference for the shop that you can use to check the accuracy of your measuring tools and they can be used in your set-ups.

I have come across the term "wring" with regard to these blocks. Can somebody tell me what this means and how it is used?

Thanks,

Tim

Rich Carlstedt
08-21-2009, 08:58 PM
Think of twisting a dish rag to "wring" out the water
You do that by placing the "Jo" blocks together at 90 degrees to each other, and twist the blocks while exerting a light pressure.

The blocks are so perfectly made, that all the air is squeezed out and molecular attraction causes them to stick to each other ( like glue !)
having the air removed is important to maintain "stack up accuracy"

These blocks were invented by Mr Johanson and were promoted by Henry Ford.
thats why the term "Jo" blocks occurs with old shop guys.

Rich

Glenn Wegman
08-21-2009, 09:09 PM
Make sure that they are clean and dust free prior to wringing!

To add to Rich's post with a little "visual"...

http://www.starrett-webber.com/GB46.html

tattoomike68
08-21-2009, 09:38 PM
First quarter machine shop student get the gage block lessons and unless you work in an inspection lab you will never touch them. You will be busy shoveling piles of chips into a dumpster.

If you have a home shop you best put them inside so they dont rust, you will never use them.

Greg Menke
08-21-2009, 09:44 PM
I have to disagree with you there- I calibrated all my mikes against a relatively cheap set bought at a flea market, all of the mikes were off, some as much as .005 from what they should have been. I discovered issues with my dial calipers too.

Certainly a 1st class set is probably overkill, but a 30 pc set of middling to low price will help a lot.

Greg

Fasttrack
08-21-2009, 09:58 PM
That is really neat! I had no idea... just a reminder of how far I have to go before I can legitimately call myself a machinist ;) :)

Carld
08-21-2009, 10:13 PM
As a machinist in a job shop I never had the need to use them. There was a set at most the shops I worked at but I only once used them and didn't really need to.

About 1995 I had the opportunity to buy a deluxe set from the International factory here and the last calibration guaranteed them to one millionth of an inch. Well, I wiped them off and lubed them and put them on a shelf and have opened the box a few times to see if they are still ok and not rusty. I did use them twice to check a measuring tool.

Oh, and yes, you can "wring" several of them together and lift them by the top block and they will stick together. It's just FM.

I seem to have a few shelf queens in my collection of tools.

JCHannum
08-21-2009, 10:33 PM
I have a very small set of gage blocks. They are Starrett, nine pieces from 0.1000" to 2.000". They get occasional use.

When checking a micrometer to a gage block, particularly one from a cheap set purchased at a flea market, and seeing a difference, how do you know that the micrometer is off and not the gage block? Or, for that matter, that both are not off. About all you can really say is that the two are not in agreement.

Greg Menke
08-21-2009, 10:47 PM
No question that in the case of a used out of calibration or cheap set the cert shouldn't be assumed to be correct- but even so, unless they're really a mess the blocks should be good to a tenth or so, plenty for calibrating mikes to a thousanth.

No way that approach is good enough for serious metrology, but its a big help for a HSM when stuff made to the same dimension using one measuring tool won't match up with other stuff made to the same dimension as measured by another.

I've found it quite interesting to see measurements taken by different mikes converge after calibration, and it does help establish confidence in the feel of dial calipers- its so easy to "press" them to make that OD measurement be what you think it should be and end up out.

Greg

oldtiffie
08-21-2009, 10:52 PM
I don't use mine all that often - but they DO get used and they can be mighty handy - if REALLY required.

Here is a pic of three of my "Jo blocks" (I am 72) "wrung" together to both set/check a micrometer and a digital inside caliper.

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Digital_caliper1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Digital_caliper2.jpg

The caliper is accurate to 0.01mm (~0.0004") and I like to make use of that accuracy. If I set the micrometer and the caliper to the "Jo" blocks I can be sure of their accuracy when set. The micrometer and the calipers effectively become comparators rather than individual measuring instruments. I get a much better assurance of accuracy that way than I would if I use the "end of range" guages that came with the micrometer and then used the micrometer to set the caliper.

Most times for work that does not require accuracy better than 0.02mm (0.0008"), I leave the slip guages in their box as the usual settings and checks for micrometers are quite accurate enough.

Most times for bores etc. I use these and a micrometer as I can "hold" an accuracy of 0.01mm (~0.0004") with care although most work is pretty easy at 0.02mm (0.0008"):
http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/idmeasdevice1.jpg

Otherwise I use machinists rulers and digital calipers. I do give my carpenters 1 metre (black and white - for optimum contrast in a dark shop or job) a good work out too as they are very accurate and as they have "inch" on one side and mm on the other they have a built-in metric/inch conversion scale!!

Its just a matter of using the tools for the level of accuracy that the job warrants.

My advice is to get a good set of slip guages as they are not expensive and are quit useful - and at times essential. They are available at Little Machine Shop and CDCO Tools (both in th USA) which are very good traders in all respects.

TxBaylea
08-21-2009, 11:00 PM
I remember that as an undergraduate Physics I set up a demonstration where I passed light between a pair of "Jo" blocks that were shimmed apart a fraction of the wave length of light (probably green) and it was polarized. I don't remember all of the details but it did work. There was some fringing since the light source was a mix of wavelengths but it did work. This was a few decades before lasers (generating a single wavelength) were discovered

Vernon

Glenn Wegman
08-21-2009, 11:07 PM
I have two sets of Starrett/Webber grade 2 gage blocks and I send one set to Webber every year for certification. After finding the best set, I keep that set certified yearly and use the second set for sine plates, sine bars, and the compound magnetic sine chuck on the surface grinder. I use them weekly as I have a Sunnen horizontal honing machine and a universal ID OD cylindrical grinder and I set bore gages using them and also verify micrometers regularly before any finish work. I wouldn't be without them! I guess it depends on what type and tolerance work you do.

Glenn

tmc_31
08-21-2009, 11:09 PM
I remember that as an undergraduate I set up a demonstration where I passed light between a pair of "Jo" blocks that were shimmed apart a fraction of the wave length of light (probably green). I don't remember all of the details but it did work. There was some fringing but it did work.

Vernon

Ok.. so... whats fringing?

Thanks guys, I really appreciate your responses. I just bought a digital mic and was checking it for accuracy when I realized that I could not be sure that my standard was accurate. Hence the search for gage blocks.

Tim

spope14
08-21-2009, 11:40 PM
I have a good set bought at an auction that I use all the time, but they also have the base, scribers, "in between" type of set-up, the good webber set with all the trimmings. Mostly I use them in setting gauges like indicals, or doing comparative measurements with an indicator or height gauge.

As for the wringing, keep them clean as noted, but I also like to use a very small piece of chamois to do a quick clean of dust and dirt before wringing. If you don't want to do this, use a piece of paper on a surface plate (keep all of this clean) to clean the mating surfaces then give a quick/light blow on them to get a very thin film of moisture for wringing. I have known some machinists to do a quick wipe by their nose (not in their nose) to get a very thin film of very light oil on them (not gooped on).

I use them frequently in setting sine bars for inspection or for very close angle milling, setting tapers on a lathe with a sine bar, and grinding angles on a surface grinder with a sine plate or sine vise. If a "production" type of mill/grind job, I do make my own "master gauge block", comparative to a set of actual blocks (grind a piece of un heat treated A2).

Depends upon what you want to do and how deep you want to get in it.

I calibrate mics on gauge pins though for the most part, bought a few of the real high quality type a few years back for when I need to calibrate for turning work. I still use gauge blocks for when milling parts calibration. Had this beat in my head in my apprenticeship to do this for whatever it may be worth, just secondary.

mechanicalmagic
08-21-2009, 11:52 PM
Ok.. so... whats fringing?
Tim

When you have two VERY flat plates (at least one transparent), in close contact, and illuminate them with one wavelength of light:
If they are PERFECTLY aligned (flat to one another), the reflected light will be uniform. If you move them apart, the light will dim, and then become bright.
If there is a very slight tilt, light and dark bands will be seen (fringes). The distance between the band is ONE wavelength of the illuminating light. A very small number. For example, a red Helium Neon laser has a wavelength of 6328 Angstroms, or about 25 millionths. It is common in the Telescope/Laser business to align and machine stuff to BETTER than 25 millionths over several inches. Mirrors are an example. I've had mirrors machined, in Aluminum, to 8 millionths over a 14" diameter.

Dave J.

oldtiffie
08-21-2009, 11:56 PM
Tim.

There are some very good posts in this thread.

Read and digest them.

The "accuracy" thing with using a micrometer both for measuring a job or checking it with any reference or guage (assuming that they are accurate) is as much "feel" as anything else.

Its highly unlikely that a good set of "shop" (Grade 2) blocks will be "out" to the extent that it will effect most day-to-day requirements in the average HSM shop.

Use the guage block stack that is closest to your required setting and use the least number possible of blocks in the stack.

If and when using any guage, leave them to "acclimatise" to the ambient temperature in the shop. Keep handling them to a minimum - use a shop-rag to keep the temperature of your hands from expanding or contacting the blocks. And of course, let the job you are checking settle down to shop ambient temperature as well.

There is no magic in slip guages - just use a bit of common sense and you will be OK.

Unless you are or need to worry about working or sizing to better than "half a tenth" (0.00005"), I don't expect that any of the afore-mentioned "problems" as regards guages or slip guages will affect you as regards their accuracy.

I don't need my slip guages to be checked or (re?)calibrated - but if I did, they would be.

Those slip guages are correct to within several millionths of an inch. There are 1,000,000 of those pesky millionths in an inch - or 1,000 of 'em in a "thou" (0.001") and 100 of 'em in a "tenth" (0.0001") - so don't get "hung up" about it all.

Its a lot more likely than not that any error will be more to do with the user/operator than it is that the cause will be the guage or the micrometer.

I'd be more concerned about the maintaining the skill-level required for YOU to measure accurately with that digital micrometer and other similar tools.

I have pretty well all the stuff Glenn Wagman has - other than the honing machine. He has a very good case to assure accuracy as he not only has the requirement but uses it regularly. My work is not quite as accurate and some (most??) of my stuff doesn't get used for months at a time. Glenn may have to insure himself while assuring customers that their accuracy requirements are met - I am only guessing here.

I have to satisfy nobody else but myself.

Glenn and I are doing things the "right way" but at different levels (his is higher) that are appropriate to our circumstances.

Slip guages are about as near as most HSM-ers will get to or need as regards absolute accuracy.

Most of use work on "relative" accuracy which is perhaps defined as "comparator" or "comparison" works where we use use one part of a pair that is to "mated" and make one part to suit another in terms of "finish" and "fit" (ie how it "looks and feels").

Its a matter of knowing what the real level of accuracy is and having the tools to do it with that matters.

Digital and "normal" micrometers and slip guages are very much included in that.

uncle pete
08-22-2009, 01:07 AM
My thoughts on Gauge Blocks. As a geneal rule most HSM types tend to buy cheaper quality measuring tools that are never sent off to a lab to be calibrated. So under these conditions then I do think a fairly good quality set of grade 2 gauge blocks are far more important than in a commercial job shop that does send their equipment out to be calibrated.

A HSM type rarely needs to measure to .0001 But does require his measuring instruments to be calibrated to a known standard so they all measure the same. A set of gauge blocks are the cheapest method to do this. Your Micrometers, Calipers, Dial indicators ect. May not then pass a quality control inspection for absolute true measurements to produce commercial tight tolerance parts, But when your making comparitive measurements so that parts fit for O.D, I.D. Length, ect, All your measuring equipment reads to the same standard, Your equipment may be able to measure to .0001 + or - but which one of the 10,000's are you measuring to? With Gauge blocks your equipment then become comparitors so that one part fits another very accurately. On the other hand your MMV. For me? Over the last 4 or 5 yrs. I've been slowly upgrading my measuring equipment to high end Mitutoyo Digital equipment more for the speed and ease of use, But would still not want to be without my Chinese built grade 2 Gauge Blocks. My Mitutoyo mics. are good to + - 50 millionth's and on all the checks I've done with them against the gauge blocks, They both agree with each other to less than .0001 deviation. That gives me a warm fuzzy feeling. You can also build parts using the previous part as a guage with no measuring involved.

Pete

jimsehr
08-22-2009, 02:08 AM
Great if cutting or checking a taper.
Jim

Paul Alciatore
08-22-2009, 04:54 AM
I have a very small set of gage blocks. They are Starrett, nine pieces from 0.1000" to 2.000". They get occasional use.

When checking a micrometer to a gage block, particularly one from a cheap set purchased at a flea market, and seeing a difference, how do you know that the micrometer is off and not the gage block? Or, for that matter, that both are not off. About all you can really say is that the two are not in agreement.

Gauge blocks are simple blocks of metal. They have no moving parts and are not used very often, even in busy shops. There are some ways they can change size, but if they are stored at normal temperatures and are not rusted or abused then these problems are minimal. Basically, if they are not distorted by excessive heat and if they do wring together, then they are probably well within the 50 millionths tolerance of grade B blocks and very close to the original calibration values.

A micrometer or a caliper is a more complicated mechanism. They do have moving parts and they are usually in day-to-day use even in shops with moderate amounts of activity and in perhaps weekly use in a home shop. They will literally see hundreds or thousands of times as much activity as blocks will. So, there are many more ways in which they can loose their accuracy: abrasion, being dropped, wear on the thread or rack or other scale, etc. This is why shops send them out for calibration. But I highly doubt that a good quality micrometer will ever be out by more than 0.0005" unless subjected to severe abuse. If you find one is off by 0.005" then read my next paragraph and take it to heart.

Finally, as Oldtiffe has stated, the operator is far, far more likely to be the source of error.

If you see an error between the blocks and the mike or caliper, I would look at the same distances generated with different combinations of blocks (0.500" = 0.050" + 0.450" // 0.500" = 0.150" + 0.350" // 0.500" = 0.250" + 0.250" // etc.) and see if the error is the same. If so, the mike or caliper is off. If not, then you can suspect the blocks. You can also look at the error at various dimensions, like 0,1", 0.2", 0.3", etc. and see if there is a common thread or if only one value is off. In short, make multiple checks before blameing either the mike or the blocks.

Glenn Wegman
08-22-2009, 12:03 PM
Its highly unlikely that a good set of "shop" (Grade 2) blocks will be "out" to the extent that it will effect most day-to-day requirements in the average HSM shop.


I belive that "shop grade" is usually Grade B, but please correct me if I am wrong.

I just looked over my certs for my Grade 2 and the largest deviation is one block that is +.000005. The rest are all from a few at -.000002 to the majority being +.000001 to +.000003". That seems pretty close for a general shop grade!

Or did I just get lucky?

Just another note: When being measured for certification each block is wrung to a flat surface so that a "wringing film" is part of the measurement so very little, if any error is added to a stack of blocks properly wrung together.

Thanks,

Glenn

Paul Alciatore
08-22-2009, 02:10 PM
Glenn,

That's better than my shop or B grade set. I have one that is 0.000026" out and many more are in the tens. One is listed as "dead nuts". I think you did get somewhat lucky.

tmc_31
08-22-2009, 02:20 PM
Thanks guys,

In reading through the posts I don't see any real differences of opinion except as to whether a HSM really needs to worry to much about those levels of accuracy beyond .001.

I will be ecstatic if I can hold +/-.001 on most of my projects. Thanks to many of you guys in another thread I am now comfortable dialing in my 4 jaw to within .001, so I am learning all the time.

Yesterday I ordered a new Starrett digital mic, measures down to .00005. I am looking forward to playing with it. I also ordered a Starrett 98-8 level. I think I will go ahead and order a good set of grade B jo blocks just so I have a good reference in the shop.

I appreciate all of you

Tim

Glenn Wegman
08-22-2009, 02:58 PM
Once again, numerous standards!

Mine are grade 2 in accordance with GGG-G-15C

Grades
They are available in various grades depending on their intended use.[2]

reference (AAA): small tolerance ( 0.00005 mm or 0.000002 in) used to establish standards
calibration (AA): (tolerance +0.00010 mm to -0.00005 mm) used to calibrate inspection blocks and very high precision gauging
inspection (A): (tolerance +0.00015 mm to -0.00005 mm) used as toolroom standards for setting other gauging tools
workshop (B): large tolerance (tolerance +0.00025 mm to -0.00015 mm) used as shop standards for precision measurement
More recent grade designations include (U.S. Federal Specification GGG-G-15C):

0.5 — generally equivalent to grade AAA
1 — generally equivalent to grade AA
2 — generally equivalent to grade A+
3 — compromise grade between A and B
and ANSI/ASME B89.1.9M, which defines both absolute deviations from nominal dimensions and parallelism limits as criteria for grade determination. Generally, grades are equivalent to former U.S. Federal grades as follows:

00 — generally equivalent to grade 1 (most exacting flatness and accuracy requirements)
0 — generally equivalent to grade 2
AS-1 — generally equivalent to grade 3 (reportedly stands for American Standard - 1)
AS-2 — generally less accurate than grade 3
K — generally equivalent to grade 00 flatness (parallelism) with grade AS-1 accuracy
The ANSI/ASME standard follows a similar philosophy as set forth in ISO 3650. See the NIST reference below for more detailed information on tolerances for each grade and block size.

http://emtoolbox.nist.gov/Publications/NISTMonograph180.pdf

oldtiffie
08-22-2009, 09:18 PM
Glenn,

That's better than my shop or B grade set. I have one that is 0.000026" out and many more are in the tens. One is listed as "dead nuts". I think you did get somewhat lucky.

That's a good comment Paul.

Just to put it into context for some others.

If ten of those blocks each had a "10" (millionths of an inch) and if all were of the same "sign" (ie +ve or -ve) then the accumulative error would be "100" (millionths) which is: = 0.000100" (yep - only a "tenth") at the worst possible case.

It is highly unlikely that there would be ten guages in a stack or that all errors were as high as a "10" or that all were all "over" or all "under" (by any amount).

As a general rule a "reference" for checking a tool (eg micrometer) should be "one order of magnitude" (which is an "up-market" or "flash" way of saying "accurate to ten times the accuracy of ......." a - say - micrometer. Which means that if the accuracy you require to be reasonably certain of in your micrometer is say "a thou" (0.001") then your guage has only to be accurate to 10x that ie "a tenth" (0.0001") = 100 millionths and if the accuracy required is to be to "a tenth" then your "guage" (eg stack of guage/"Joe" blocks) needs to be accurate to a "tenth of a tenth" of an inch = 0.0001/10 = 0.00001 = 10 millionths of an inch.

A good Grade 2 or "B" (same thing) will get you there - providing that all other good measuring conditions (read" "Metrological") conditions are met.

So, all in all, there is an excellent chance that a good set of "Shop Grade" ("2" or "B") will be all that you need - if and when you need them.

There is no practical point in worrying needlessly as the accuracy should only be as good as the job requires.

That accuracy includes working to sensible limits in terms pf measuring, machining and the use and purpose of the parts being made. Those limits are not just "how close it measures" but how good the quality of the finish is.

The closer you go to those limits the "better" and"more accurate" you have to be. Conversely, there is no point in working to "tenths" if there is say "5 thou" (0.005") between the "high" and "low" limits as you have a tolerance of +/- "two and a half thou" (0.0025") from the centre of those limits. I always aim for the centre/middle or the amount that gives me "most to play with" - ie I go "large" on a shaft and "small" on a hole so that I have maximum "meat" left to remove if necessary.

I've seen people worry needlessly here about positional and diametrical accuracy in the "small thous" (or less!!) for what are 1/16" clearance holes on a pitch circle on a mill. If it were me, I wouldn't bother putting it on my mill as I'd probably mark it out on my "marking out table" (sheet of "float" glass on my mill table using a machinist's ruler and a scribing block or surface guage), centre-punch it and drill it in the pedestal drill.

I will address a few other items regarding "accuracy" later.

Glenn Wegman
08-22-2009, 10:21 PM
A good Grade 2 or "B" (same thing)


Gage Block Specifications from MSC Big Book. Page 1329:

Up to 1" for Grade 2 = +4 /-2
Up to 1" for Grade B = +10/ -6

2" Grade 2 = +8/-4
2" Grade B = +10/-6

3" Grade 2 = +10/-5
3" Grade B = +20/-12

4" Grade 2 = +12/-6
4" Grade B = +40/-24

Millionths of an inch

Considerable difference in price too!

Webber Grade B $250.00
Webber Grade 2 $1220.00

Glenn

bborr01
08-22-2009, 10:59 PM
I have done quite a lot of high precision grinding and frequently used gage blocks. I used them to set electrolimit gages for checking parts waaaay closer than you could check with a micrometer. I also would use them on a surface plate with a tenth indicator to check parts. When I was running mills and lathes, etc. I rarely used blocks. The closer the tolerances you need to hold, the more you will use jo blocks. edit: PS. I think the thing that holds them together is molecular cohesion.

mechanicalmagic
08-23-2009, 12:29 AM
In the Home Shop, a set of Jo blocks, and a sine bar is the best way to set precise angles or tapers.
Jo blocks are also a very good way to check that larger flea market micrometer.

In spite of what others have reported, I have a set of blocks, cheap Chinese, supposedly good to better than +-.0001". Of the many I have checked, they are ALL on the long side. YMMV.

Dave J.

boslab
08-23-2009, 01:16 AM
I did a course in engineering inspection some years ago, to be honest slip gauges were the bread and butter of inspection, they were not off the bench [surface plate] at all, all measurements were slip stacks up to the limit of the set, vernier height gauges were also used with suspicion [they were not digital!] tower mikes preferred when tallish measurements being made.
I dont know how to use a sine bar/table/compound table without slips and a good clock/stand, if you have slips or jo blocks on the shelf why not use them?.
dont leave them wrung, they can weld if left! [takes months but they will if they are a good set, when you do seperate them the surface is ripped off, they will never wring again]
I wont ask if anyone has an optical flat!
Co-ordinate marking out with slips/surface plate/angle plate was an early exercise, hole positions etc easily done, definatly somthing to be used where possible.
mark

J Tiers
08-23-2009, 01:39 AM
Why would anyone worry whether the cal on the blocks is current?

Using the minimum# of blocks....... and blocks that are grade B, not a very accurate grade to start with...... with all errors in same direction.... you might possibly be 0.3 tenth off, which is under a micron. Likely not that far off, not all one direction (chinese blocks need not apply)

Your mic reads to tenths........

So the worst error is 3x better than the resolution of the tool you are checking..... what's the problem?

If you say the blocks are out of cal and therefore that they are off size....... then you have to show us the mechanism for their growth or shrinkage...... If they have sat with only a few uses, and still wring..... how did they suddenly get bigger or smaller?

Nope, the purpose of a 'cal" is NOT to improve accuracy, it is to PROVE it to third parties.

If you don't need to PROVE accuracy, then calibration of gage blocks serves no purpose unless they are heavily used.

oldtiffie
08-23-2009, 06:54 AM
First, the OP's query:

Hey guys,

I have been reading about gage blocks. My understanding is that they are a standard reference for the shop that you can use to check the accuracy of your measuring tools and they can be used in your set-ups.

I have come across the term "wring" with regard to these blocks. Can somebody tell me what this means and how it is used?

Thanks,

Tim

answered:

[edit] Adhesion
Wringing is the process of sliding two blocks together so that their faces lightly bond. When combined with a very light film of oil, this action excludes any air from the gap between the two blocks. The alignment of the ultra-smooth surfaces in this manner permits molecular attraction to occur between the blocks, and forms a very strong bond between the blocks along with no discernible alteration to the stack's overall dimensions. Guage blocks, when properly wrung, may withstand a 200 lb (890 newton) pull. The detailed physics responsible for this phenomenon remains unclear.[1] Possible causes that have been suggested are: atmospheric pressure, molecular attraction, a minute film of oil, or a combination of these factors.

from:
http://en.wikipedia.org/wiki/Gage_blocks

Now back to to issues raised since:

Gage Block Specifications from MSC Big Book. Page 1329:

Up to 1" for Grade 2 = +4 /-2
Up to 1" for Grade B = +10/ -6

2" Grade 2 = +8/-4
2" Grade B = +10/-6

3" Grade 2 = +10/-5
3" Grade B = +20/-12

4" Grade 2 = +12/-6
4" Grade B = +40/-24

Millionths of an inch

Considerable difference in price too!

Webber Grade B $250.00
Webber Grade 2 $1220.00

Glenn

Thanks Glenn.

I checked my guage blocks and they are "Grade 2" "Vertex" certified in accordance with ISO DIN 861 as we are "metric" in OZ.

Sorry about that. I should have checked first.

ISO DIN 861 is now DIN EN ISO 3650

Here are the tolerances for metric guage blocks - including "Grade 2":

(Note: these dimensions are in micrometers = um = 1 millionth of a metre (or 1 thousandth of a mm) ~ 40 micro-inches):

http://www.measureshop.biz/en/measuring-instruments/gauge-blocks-and-accessories/

http://www.google.com.au/search?hl=en&source=hp&q=iso+din+861&btnG=Google+Search&meta=&aq=f&oq=

Here are the various grade (from Wikipedia):

Grades
They are available in various grades depending on their intended use.[2]

reference (AAA): small tolerance ( 0.00005 mm or 0.000002 in) used to establish standards
calibration (AA): (tolerance +0.00010 mm to -0.00005 mm) used to calibrate inspection blocks and very high precision guaging
inspection (A): (tolerance +0.00015 mm to -0.00005 mm) used as toolroom standards for setting other gauging tools
workshop (B): large tolerance (tolerance +0.00025 mm to -0.00015 mm) used as shop standards for precision measurement
More recent grade designations include (U.S. Federal Specification GGG-G-15C):

0.5 generally equivalent to grade AAA
1 generally equivalent to grade AA
2 generally equivalent to grade A+
3 compromise grade between A and B
and ANSI/ASME B89.1.9M, which defines both absolute deviations from nominal dimensions and parallelism limits as criteria for grade determination. Generally, grades are equivalent to former U.S. Federal grades as follows:

00 generally equivalent to grade 1 (most exacting flatness and accuracy requirements)
0 generally equivalent to grade 2
AS-1 generally equivalent to grade 3 (reportedly stands for American Standard - 1)
AS-2 generally less accurate than grade 3
K generally equivalent to grade 00 flatness (parallelism) with grade AS-1 accuracy
The ANSI/ASME standard follows a similar philosophy as set forth in ISO 3650. See the NIST reference below for more detailed information on tolerances for each grade and block size.

from:
http://en.wikipedia.org/wiki/Gage_blocks

There may be some confusion between the metric micrometre (um) = 1 millionth of a metre, and a micro-inch which is 1 millionth of an inch. It should be self-evident that there are ~ 40 micro-inches in a micro-metre.

There are about 25 (25.4 actually) millimetres (mm) in an inch and a 1/25 ~ 0.040" it follows that a mm is ~ 0.040"

The USA inch is specified in terms of a metre (1 = 0.03937 metres) and is also + 25.4mm

There are about 40 (39.37 actually) inches in a metre so it follows that there are ~ 1/40 ~ 1000/40 ~ 25mm in an inch.

On February 10, 1964, the National Bureau of Standards (now known as the National Institute of Standards and Technology) issued the following statement:


Henceforth it shall be the policy of the National Bureau of Standards to use the units of the International System (SI), as adopted by the 11th General Conference of Weights and Measures (October 1960), except when the use of these units would obviously impair communication or reduce the usefulness of a report.[2]

from:
http://en.wikipedia.org/wiki/Metrication_in_the_United_States

Which explains why there are so many 40's and 25's in NIST standards and reports.

NIST measures in the metric system and "soft converts" (multiplies or divides by both 25 and 40 to get a "soft-converted" "inch" measurement.

OK - now back to Glenn Wegman's post:




Originally Posted by oldtiffie
A good Grade 2 or "B" (same thing)

Gage Block Specifications from MSC Big Book. Page 1329:

Up to 1" for Grade 2 = +4 /-2
Up to 1" for Grade B = +10/ -6

2" Grade 2 = +8/-4
2" Grade B = +10/-6

3" Grade 2 = +10/-5
3" Grade B = +20/-12

4" Grade 2 = +12/-6
4" Grade B = +40/-24

Millionths of an inch

Considerable difference in price too!

Webber Grade B $250.00
Webber Grade 2 $1220.00

Glenn

My calling my blocks Grade B instead of Grade 2 - has been dealt with.

Glenn's table had the following allowances:

Up to 1" for Grade B = +10/ -6

2" Grade 2 = +8/-4

3" Grade 2 = +10/-5

4" Grade 2 = +12/-6

Millionths of an inch

That is a total of + 40 to - 21 millionths of an inch over 10" which is an accuracy range of 40/10 = +4 to 21/10 = -2 millionths of an inch per inch.

That is the absolute maximum and the chances of all guages being both at their limits and all +ve or all -ve are pretty slim.

So as we are mainly talking "inch" for those in the US, those terms in "real life" are as follows:
+40 x 0.000001 = 0.000040" = 0.4 of a "tenth"
-20 x 0.000001 = 0.000020"= 0.2 of a "tenth".

There are the worst possible cases over 10" in the blocks that Glenn used as examples.

The Grade "B" totals were:
+80 to -42, which is not too bad either.

I don't worry about that too much as regards either set in my shop.

I see a lot about the accuracy of surface plates and their various grades - and that is how it should be.

I did a thread on surface plates and how good or bad my black granite Grade 2 surface plate was. It was very accurate. But whether that sort of accuracy is really needed in a HSM shop is open to debate.

I have no issues with anyone buying these precision tools as they are very accurate, cheap and readily available.

All of those slip guages and surface plates have been guaged and certified at some point in their lives. The chances of any significant wear or distortion over a long period in a HSM shop is pretty negligible.

I do have issues with sine bars, sine plates and all their derivatives and relatives though.

Other than in an "Inspection Department", or Metrology laboratory etc. I have never seen one that is certified at all let alone fully certified.

Only some of the things that I'd expect o be certifies would be:
- rollers: size, straightness, round, parallel (to each other and the base of the sine bar);
- top and bottom plates: flat; parallel, square
- etc.

A sine-bar was set at an arbitrary 10" (and 5") between the roller centres as it was easier when using printed trigonometrical "sine" (of angles) tables in "log(arithm) books" which in most shops were correct to 5 decimal places and 6 (or better) places in Tool-Rooms and "Inspection". So for any angle when using those "Sine tables" all that was necessary was to move the decimal point "one place right" and you had the "block" you needed for that angle on the sine-bar. (No electronic calculators, let alone computers then!!!.).

Sine bars are notoriously less accurate as the angle moves toward 30 degrees and are highly questionable at or above 45 degrees.

Setting an angle with a sine bar - and of course "slip guages" - is all very well but to use a sine bar to measure an angle is all too often not so accurate at all as the slip guages are pretty well used as "feeler guages" to get the "best fit" which is more subjective ("think so" - or plain guessing) than it is objective (known accuracy and setting of guage blocks).

Setting a job to a set angle with a sine-bar on a mill or grinder requires the axis of the rollers to be very accurately "square" to the mill or grinder table axis else you are well and truly into the dreaded (and rightly so) "compound angles".

An "error" of a "thou" (0.001") on a 10" sine bar is only "1 tenth per inch" (0.0001" per 1.0000").

Now "1 tenth per inch" = 0.0001/1 is the asin of 0.0057 degrees which is 20.627 arc seconds which is quite within the capability of pretty well any quality rotary table (and very much inclusive of my "Vertex" rotary tables).

I use my rotary tables and excellent "Vertex" angle blocks
for most angles. The angle blocks are very versatile - especially if used with imagination and lateral thinking.

Paul Alciatore wrote one of the most instructive articles I've seen on them not so long ago in one of VP's magazines.

I will cover them as regards angular measurement and settings in a future post.

Glenn Wegman
08-23-2009, 08:20 AM
If they have sat with only a few uses, and still wring..... how did they suddenly get bigger or smaller?


I wonderd the same thing quite some time ago! I found the answer on the Starrett Webber web site when I first purchased my blocks. The website has now been changes and I can't find the information.

I am not at all up to speed on heat treating....but it seems it is a problem with steel blocks and is related to the heat treat process used wherin the block can actually change size over time. I believe that the usual tendency is to grow larger. Another factor is that both Webber and DoAll sell "gage block stones" on which you rub the blocks to clean them prior to wringing. Some just slide them a short stroke on a clean granite surface plate. Over a period of time minor dimensional changes are possible. If you have a block that won't wring, slide it up and back about an inch ot two on the clean granite, it works!

I'm curious to see how mine do. I bought them used (from Australia) and they had been calibrated when I got them. After a year, I sent them to Starrett/Webber for cal and didn't really pay too much attention to any differences since it was two different labs in two different countries. Next year, they will go back to Starrett/Webber so I'm curious to wheather there will be many differences as compared to the previous cal.

Glenn

J Tiers
08-23-2009, 11:28 AM
I suppose the issue is not whether they change at all, but whether they change a significant amount. I know about the slow change issue, and it's generally quite small, IIRC

If it were a really important amount, like 0.5% for some material, it would be well-known, and blocks would not be made of that stuff anymore......

If your needs are for tenths only, you'll likely never see an issue unless you stack up a bunch of same-direction limit case tolerance error blocks.

Glenn Wegman
08-23-2009, 03:52 PM
If it were a really important amount, like 0.5% for some material, it would be well-known, and blocks would not be made of that stuff anymore......


Exactly!

That is why the switch to Chromium Carbide and/or Ceramic blocks for the high end stuff. Bring an extra wallet though!

Agreed that it is usually an insignificant amount. I had to look into it as I initially could not get a grip on why certification was necessary on a square haed piece of steel. I have a girl working for me that retired from Grumman Aircraft and had worked in the inspection dept. She stated that even 6" pocket scales had to be calibrated/certified at regular intervals!

Evan
08-23-2009, 04:23 PM
Gauge blocks are for people that need traceable standards of calibration. The HSM is surrounded by standards that are more than accurate enough for just about anything. I calibrate my tools as I use them. Just this morning I used two different calipers to measure several precision ground shafts and the ID of the bearings that fit. I use a lot of metric and SAE hardware so I measure just about every part I pick up because there are some very close but not close enough near matches in the two systems.

If I measure three different items that are supposed to be 0.375" and all three read the same on two different calipers with that reading being the needle exactly nailed on the clock mark then the chance that anything is out of calibration approaches zero times zero. You can also use instruments to measure each other in a round robin and if they all agree then again, the chance of some sort of error that affects all three equally is negative zero. You can also measure items that are manufactured to very close tolerances such as bearing races and many types of cutters.

I measure just about everthing I pick up to use since that way I can be fairly certain I didn't misread the tiny markings that are on most quality tool bit.

Why is it that the cheap tooling has the most readable size markings and the expensive tooling require special lighting, stereo magnification and an annular eclipse of the sun to read?

Glenn Wegman
08-23-2009, 04:44 PM
I use a similar method of cross checking. I'll wring up a stack of gage blocks to the desired dimension and clamp a mic on them and lock the spindle.Then set a bore gage (.0001") to the same stack of blocks, and then check the bore gage in the mic to see if they agree. If everything agrees, I'm most likely good.

Most older machinists have a drawer full of larger size dowel pins that I figure they use to check mics and spindle or chuck runout etc..

oldtiffie
08-23-2009, 08:56 PM
Originally Posted by J Tiers
If it were a really important amount, like 0.5% for some material, it would be well-known, and blocks would not be made of that stuff anymore......


Exactly!

That is why the switch to Chromium Carbide and/or Ceramic blocks for the high end stuff. Bring an extra wallet though!

Agreed that it is usually an insignificant amount. I had to look into it as I initially could not get a grip on why certification was necessary on a square haed piece of steel. I have a girl working for me that retired from Grumman Aircraft and had worked in the inspection dept. She stated that even 6" pocket scales had to be calibrated/certified at regular intervals!

Quite so.

In many HSM shops, absolute accuracy is confused with relative accuracy.

For example, is the HSM-er has a shaft that he is making a bearing for, most times all he wants to know how much "over" he has to be and what his limits are. He might measure the shaft with any micrometer - previously "zero-ed" against itself at "zero" (closed) if it is a 0 -1" micrometer or against the checking "stick" that came with anything larger (ie a 2" "stick" to check a 2" -3" micrometer at the micrometer "zero".).

He is now "set to go".

If the bearing tolerance is say "shaft size" +0.002"/+0.004" he knows that he has "2 thou" to "play with". So, provided that he is within the limits of the bearing tolerance he is OK. There is no need to work at the limits - just anywhere between them.

Provided his surface finish is OK he has done a good job.

He could even be "out of round" by those limits or even have a taper within those limits and still be OK.

If he is sensible he will "stay inside" the limits by say "half a thou" (0.0005") each (a total of 0.001") and he has a relatively easy job with still a "thou" left to work/"play" within.

And not sign of a slip guage or a surface plate in sight - or needed.

"Inspection" or "calibration" are used to determine both relative (how "good" or not compared to another part) or absolute (the absolute dimension related to known standards).

It is usually to "warrant" that a part is "to specification" using specified procedures with pre-calibrated and/or pre-certified tools etc.

JT pretty well nailed it when he said - as I recall - that it was to be able to assure a "customer" that you have met that customers specifications by relying on pre-certified instruments at an accuracy of at least a specified order of magnitude "better" than the instruments you used on the customers order.

Its a matter of justifying your charges if you got it right and to be able to blame the person who certified your equipment if the customer proves or says you got it wrong.

All "customers" (clients) are not "external" (somebody outside your company). It may well be "internal" (somebody else in the production/use "chain" in a series of processes).

From the point of view of the average HSM-er, this, more often than not, is not applicable or an issue at all other than as a discussion topic or "nice to know".

For most of us, just knowing what we really have to do and doing it is quite adequate.

There is no reason to impose unnecessary "degrees of difficulty" with the usually exponential rise in costs if it is not necessary.

If you do HAVE to work to "tenths" - fine. Then you have to have the tools and the skills to do it and measure it.

If you DO NOT have to do it, you have several options:
- do it anyway just to suit yourself; or
- go back and only do it sufficiently well to have the job do what it is intended for; or
- a mix of both the previous options.

Just "because you can" does not or need not mean that you MUST.

And conversely, if you cannot but don't need to anyway but can turn out a job that it "fit for purpose" - you are quite successful.

I have some fairly "high end" stuff that never sees the light of day from one months (years??) end to another because I've found a more basic way of doing the job. Some of it only gets used when I decide to "give it a go/run" and/or "just to see if it works" or to see if I can still "use it" - if or when I can find it!!!.

My general attitude is that if I find myself having to work closer than a "thou" or two, I need to go back and see why. If I have to do it - I do it. If it turns out that I don't have to - I don't.

I suggest that some go back and re-read JT's and Evan's recent posts as they make a lot of very practical sense and throw the required buckets of cold water where needed:


Why would anyone worry whether the cal on the blocks is current?

Using the minimum# of blocks....... and blocks that are grade B, not a very accurate grade to start with...... with all errors in same direction.... you might possibly be 0.3 tenth off, which is under a micron. Likely not that far off, not all one direction (chinese blocks need not apply)

Your mic reads to tenths........

So the worst error is 3x better than the resolution of the tool you are checking..... what's the problem?

If you say the blocks are out of cal and therefore that they are off size....... then you have to show us the mechanism for their growth or shrinkage...... If they have sat with only a few uses, and still wring..... how did they suddenly get bigger or smaller?

Nope, the purpose of a 'cal" is NOT to improve accuracy, it is to PROVE it to third parties.

If you don't need to PROVE accuracy, then calibration of gage blocks serves no purpose unless they are heavily used.


Gauge blocks are for people that need traceable standards of calibration. The HSM is surrounded by standards that are more than accurate enough for just about anything. I calibrate my tools as I use them. Just this morning I used two different calipers to measure several precision ground shafts and the ID of the bearings that fit. I use a lot of metric and SAE hardware so I measure just about every part I pick up because there are some very close but not close enough near matches in the two systems.

If I measure three different items that are supposed to be 0.375" and all three read the same on two different calipers with that reading being the needle exactly nailed on the clock mark then the chance that anything is out of calibration approaches zero times zero. You can also use instruments to measure each other in a round robin and if they all agree then again, the chance of some sort of error that affects all three equally is negative zero. You can also measure items that are manufactured to very close tolerances such as bearing races and many types of cutters.

I measure just about everthing I pick up to use since that way I can be fairly certain I didn't misread the tiny markings that are on most quality tool bit.

Why is it that the cheap tooling has the most readable size markings and the expensive tooling require special lighting, stereo magnification and an annular eclipse of the sun to read?