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Micrometer accuracy

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Micrometer accuracy  Empty Micrometer accuracy

Post by Froneck Wed Nov 29, 2023 5:11 pm

I purchase a set of Starrett Gauge blocks A1 accuracy standard that means +/-.000006". To help those on this forum I'll test your mic at 3 dimensions for $5 + shipping. Not sure what shipping will be but it will be the same as the cost for you to ship it to me. I doubt if anyone uses a larger than 1" mic but the gauges will allow me to test up to 6". I can do calipers too but the gauge accuracy is overkill.

Froneck

Posts : 1672
Join date : 2014-04-05
Age : 76

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Post by WesG Wed Nov 29, 2023 8:55 pm

I've checked my Mitutoyo and Etalon mic's on Lufkin blocks .... my first Tesa dial caliper was dead on all the way to 6" ...

Gun stuff ????

Pffffff .....

'Schlock Verk' ... as my Grandfather called it.

WesG

Posts : 631
Join date : 2018-09-21
Location : Cedar Park, TX - N CA

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Post by jmoore Thu Nov 30, 2023 1:41 am

A very good deal, if you need it. I used to get 30 some odd precision measuring tools calibrated yearly, happily at my employer's expense. I still have access to standards for unofficial calibrations. You might be surprised at how close some calipers can be over their entire range, BTW. Other calipers? Might as well use a tape measure...

Micrometers do get wonky with lots of use. And sometimes the faces get well out of parallel!

jmoore

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Join date : 2021-11-04

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Post by Froneck Thu Nov 30, 2023 5:24 pm

Accuracy of a good digital caliper by Mitutoyo or Starrett is +/-.001" that results in a .002" accuracy range. Standard .001 reading Starret is accurate to +/- .0001" if it is a .0001 reading micrometer it's accurate to +/- .00005.
 Test should be made at dimension needed. Quite a few micrometers are used on one size so they wear at that point, if there is a dimension that is measured quite a bit the accuracy should be tested there. Interesting a Starrett Digital Micrometer accuracy is +/- .0001"
 Accuracy is from Starrett and Mitutoyo Catalog.

Froneck

Posts : 1672
Join date : 2014-04-05
Age : 76

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Post by WesG Thu Nov 30, 2023 8:50 pm

Accuracy at "some dimension' is BS  ...

Its the full scale... of the 'user-centered' you're using  

Which comes back to a 'screw' ... and the thimble attached to it ...

WesG

Posts : 631
Join date : 2018-09-21
Location : Cedar Park, TX - N CA

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Post by Froneck Thu Nov 30, 2023 9:39 pm

Not really, the mic. may  be Zero when closed and if a 1" standard is used read exactly 1" (assuming it's a 1" micrometer) yet at some place between the range be off! It's the same as on a lathe or milling machine that relies on the "screw" just like the micrometer. If the machine were used in the production of a single item the screw will be worn at that point. I can't tell you how many times I had a machinist say I moved the cutter .010" and it cut .010", took another cut .010" and in did remove .010" then I took another cut .010" and .024" was removed and part is no good! Yet the next item attempted the same thing happens! Simply put the screw was worn!
 If an item has to be .5000" and a mic that that is worn at .5000" it's useless unless it is calibrated at .5000"!!! I have picked up quite a few micrometers, they have a nut on the threaded section that will tighten the nut to compensate for wear. But if it was worn in one spot the screw will be to tight and hard to turn when at the unworn section!
 If I need to make a part and mic the sample with any untested mic then use the mic to measure the part I make it will be OK! Why because if the mic error was .-003" at the measuring point it will still be -.003" when I mic the part I'm making therefore both are the same size! But if a print has a dimension and my mic. has the error of -.003 The part will be .003" oversized! To be accurate the mic. or any measuring tool has to be checked at the point the finial measurement is taken!!! Yes Starrett mic.s have very accurate screws and nuts as well as other top brands but if used repeatedly at one point the screw and nut will wear! I can assure you that if I'm making a part the the print has .6250 +/- .0005 I'll check the mic. at that point with gauge blocks!

Froneck

Posts : 1672
Join date : 2014-04-05
Age : 76

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