How to calibrate micromenters

[Naphtali]

I acquired a set of Brown & Sharpe vernier outside micrometers, some of which need calibrating. I have adjustment wrenches for calibrating, but I have no gauge blocks. If it is possible to calibrate without gauge blocks, please identify the procedure. If it is not possible, what should I expect to pay for a machine shop to do it?

[smokeywolf]

Place a clean piece of paper on the anvil and gently close the spindle down on the paper. Object is to put enough pressure on the paper so that you can with little effort, drag the paper out from between the measuring faces, transferring any dirt onto the paper that may have been on the measuring faces. Do this two or three times. Then, with a clean dry fingertip, wipe away any paper particulate that may have been left behind on the measuring faces.

Now, run the thimble face down GENTLY against the anvil, ideally using the same light pressure that you will use when measuring parts, cutters, boolits, etc. Now check to see that the "0" division on your thimble aligns with the "0" witness mark on the barrel. If it does not, then use your wrench to achieve "0".

This gives you half of the calibration. You now need to find standard or Jo Block to check the outer limit of the mike.

smokeywolf

[MtGun44]

If it is a 0-1, then clean and close to set to 0 properly, as stated in more
detail above.

For the 1-2 and larger, you need the gage blocks, which usually came with
the mics. I have up through 5-6" and all the gage blocks are there
in the original mic boxes.

[georgerkahn]

Both posts (#2 & #3) are most sound. I reckoned I'd add my 1 1/2 cents ;) ... I, too, had an out of whack micrometer (a Brown & Sharp) and, lacking a standard, got the not-so-brilliant idea of using brand new drill bits as my calibration reference. I soon learned that what's imprinted on said drill bits ain't (sic) necessarily the true diameter. I've since acquired a standard. However, thought I'd share my "brilliance" re using drill bits as a reference to perhaps calibrate your micrometer -- NO!
BEST!
georgerkahn

[KCSO]

If you have a mic that is on and a sample to check you can cross check using a block or drill rod measered in the good one and checked against the other . This is not perfect but it will disclose any major (.001 or more) defect.

[NSB]

At one time I managed two metrology labs and had to do gage calibrations on every gage in the system. I've never found a set of mics that were set to zero (not talking digital here) that were out of calibration unless they were dropped or damaged. I'd check the same set time, after time after time, and they were always right on. They don't go out of calibration from use, they get off "zero" and need to be checked by the operator before use. Gage blocks are nice, but if you haven't dropped or damaged your mics, they are probably just fine for use even in a machine shop. As stated above though, they must be very clean when setting to zero. A lot of people don't realize how little dust, or even a finger print, can change the zero setting.

[KCSO]

Forgot to add if you don't have gauge blocks a set of 123's work nicely.

[bob208]

short answer you need gage blocks. others have left out the important first step. on o-1 after the anvils are clean close them hold them up to a light and make shore they are flat together. on larger mics. you have to close them on something that has 2 flat and parallel sides. to check that they are squire.

[sparky45]

I have a very old Reed Small Tool Works Micrometer that, well for a lack of a better term "over travels" when seeking zero. No more than .005", but that makes it out of cal. How do I fix this problem?

[aspangler]

I am surprised no one has mentioned using feeler gauges such as a gunsmith would use. Not the mechanics feeler gauges. Also how about pin gauges?

[oldracer]

As noted, if the mic is 0 to 1 then check and set the 0 if necessary. You can also use drill bits from a very good set although I found my cheapo Harbor Freight set was as near perfect as the set that was donated by the Navy about 35 years ago! For the two larger ones I had, I went to a machine shop and used their blocks to check mine and since I had the needed tools they were impressed enough to let me do it for free.

[cwheel]

Be careful about 123 blocks, some of the imports are a ways off and wouldn't be good to set up micrometers with. While they are usually ground in sets, I've seen imports as far off as .0015. Best way is always use gages or gage rods that come with most quality micrometers. (B&S is usually a very good quality micrometer ) I'd recommend finding another machinist that has these, it's a very common thing for most machinists to have standards to set micrometers up their own micrometer sets to 6" and most wouldn't mind helping you out with this as it's usually fast to do or check. As stated well above, the 0-1 is the easiest to set using itself as the standard. Good luck,
Chris

[smokeywolf]

If you don't have anything else, gage pins are better than nothing. Drill blanks are usually .0002 under nominal. Reamer blanks are typically .00015 to .0002 over nominal. As far as determining if measuring surfaces are parallel to each other, optical flats are the tool for that.

[doc1876]

I agree with the previous posts. if you wish to check your micrometer then the 1 2 3 blocks are a good idea ,but try and use a machinist custom made set

[Ballistics in Scotland]

I have a very old Reed Small Tool Works Micrometer that, well for a lack of a better term "over travels" when seeking zero. No more than .005", but that makes it out of cal. How do I fix this problem?

This is the easy one. There is usually a little wrench provided (but you can find them on eBay). Just insert it in the little hole in the sleeve, and rotate the sleeve until the marks for zero come into line. You aren't changing where the moving parts come to, but where the sleeve figures say it is.

In theory you should check accuracy at the other end of the micrometer's scale as well, or somewhere well along it. But that is less important. Any kind of severe knock is liable to distort the frame, but it will affect all measurements equally. The only thing that could affect one end of the scale and not the other would be wear on the threads, which is less likely.

[sparky45]

Thanks for the reply, I don't have a wrench, but I will try and buy one.



This is the easy one. There is usually a little wrench provided (but you can find them on eBay). Just insert it in the little hole in the sleeve, and rotate the sleeve until the marks for zero come into line. You aren't changing where the moving parts come to, but where the sleeve figures say it is.

In theory you should check accuracy at the other end of the micrometer's scale as well, or somewhere well along it. But that is less important. Any kind of severe knock is liable to distort the frame, but it will affect all measurements equally. The only thing that could affect one end of the scale and not the other would be wear on the threads, which is less likely.

[Big Rack]

If it's a econo model the outer thimble is attached to the threaded stem with a setscrew if dropped they may be out a bunch. Unscrew the thimble cap you'll see the setscrew, clean and close loosen setscrew and put thimble on zero and tighten.
Kind of finicky but preserves the position of the zero line.
For the guy with the mics that won't repeat, maybe threads are worn or if lucky the the thread adjustment collar may need tightened.

[zuke]

Look on EBAY for single gauge block's. I've picked up several set's cheap, and their brand new in the box

[W.R.Buchanan]

I agree with NSB on this one. I haven't recalibrated my mics in my shop for 20 + years.

However I am the only one who uses them so I know what has happened to them along the way.

This stuff doesn't change by just sitting around in a box or tool chest.

Now Calipers are a different story, and I check mine for zero virtually everytime I pick them up. They can and do get bumped around and do change.

Also wiping the anvils of your tools with your bare clean fingers before closing them will remove foreign matter than you will miss with cloth or paper.

Randy

[JonB_in_Glencoe]

Before I got a 1/4" x 1" standard, I used commercial J-words as redneck standards.