Calibrate Mics

[bosterr]

I have a 1" electronic digital mic I got from Reid Supply and an analog 1" RCBS mic. Neither came with directions, but that's not my issue. How does one know if it's calibrated correctly? One can't rely on a .375 jacketed on measuring right on .3750 or a 1/4" drill bit shank measuring right on .2500 either. My perfect solution would be a gauge block that would allow me to check 3 ways across the range, say at .3750 and .6250 and 1.000. I really didn't want to spend a lot of money on a huge set, just something to calibrate within our requirements such as measuring boolits dropped as cast, boolits after sizing and lead slugs after slugging bores. I've done a lot of searching online and haven't found what I need yet.

[country gent]

On 0-1" mics you can set zero by closing to your feel and checking the reading. Measuring 4 times every .025 will tell you if the faces are square and parrallel. Measuring alont thier range will show thread wear in a certain spot. (If zeroed and .5 measures .502 and .750 measures .750 then there is thread wear in the .500 range). Calibrting a set of mics is pretty straight forward. verifying accuracy thru their range is alot more work. At work ( tool gage room) on touchy jobs we would check micks with Jo blocks or pin gages at the measurement to insure they were accurate there. If we needed a .500 pin +/- .0002 we would measure a .5 pin gage and then check the hole if both read the same on the mics we knew we were right

[bosterr]

Ok! I measured a hex sided screw gun bit with both mics after zeroing both to "my" feel at the exact same place 6 times each. The electronic digital measured at .2487 and the analog measured at .2491 for a difference of .0004. Then I measured a drill bit shank that wasn't all roughed up. The digital measured 6 times at .3726 and the analog measured at .3731 for a difference of .0005. I could adjust the analog to read the same as the digital to satisfy my OCD, but a difference of .0004/.0005 will probably be good enough for what I do. Thank you country gent for your help!

[country gent]

To get down to reliably measure to .0001 or less you almost need a controled atmosphere . temperature, humidity, pressure need to maintined at a constant. Also parts need time to "normalize to this. For what most reloaders and gunsmiths do you are more than close enough.

[Ballistics in Scotland]

The instruments reading zero when you are measuring nothing is a good start. If you search on eBay for a 1in. micrometer standard, you will find fairly cheap ones which in this size are usually hard steel rods with slightly rounded ends, and sometimes a plastic sleeve to stop the warmth of your fingers from causing expansion.

Yes, there are faults of micrometers which can cause them to read inaccurately when zero and 1in. are accurate. But they are slight and infrequently found, and of little importance to the handloader or practical gunsmith.

[Mitch]

sounds like you have them set good enough for what we do.if my boolits need to be within .0001 I am in trouble.all kidding aside..most gun shows have someone selling used presision tools.so look around abit for gage pin of jo block.the size realy wont matter as long as you know the size.
one other thing a lot of people do not realize is feel.I know for a fact country gent and I have been using mics for more then 38 years.I would bet that if I was to use his mic I would get slight difference with his tools than mine.and he with mine.so unless you use the mics every day the few tenths differeance you are getting from one mic to another is your feel.

[smokeywolf]

bosterr, Don't forget to clean the measuring faces. This is done by closing the thimble down to where it is nearly closed, insert a sheet of scrap paper between the measuring faces, close the thimble down so that the paper is held lightly by the thimble and anvil measuring surfaces. Pull the sheet of paper out so that it wipes the measuring surfaces as it is pulled out. I usually follow this procedure by blowing a puff of air across the measuring faces to make sure there is no paper fluff (particle) left behind.

Only after the measuring faces have been cleaned can you check "zero" on your mike.

Buy a 1 inch standard (typically about $15.00 used) and check your mike at "0" and "1" inch.

I've yet to see a name brand micrometer that is less than 50 years old, off more than a tenth (1/10,000 of an inch) anywhere between "0" and "1".

[bosterr]

Thank you all for your help. No doubt I'm trying to split hairs, just my nature , I guess. I don't cast anything smaller than .311, so +/- .0005 is close enough. And those are shooting extremely well.

[country gent]

The reason we checked michrometers the way we did was production tools see alot of wear in one place or very limited use of the full range. A michrometer on the line being opened nad closed to a set dimension every time day in and day out created some very localized wear in the thread. We would start new mics out at the stations with the smaller parts if possible and as they got worn rotate to stations where the parts were bigger and they would be back into better threads. Once the entire range was ran thru we then lapped the threads and reset the collet basically rebuilding them back to accurate tools. Production tools see alot of localized wear and use

[smokeywolf]

Thanks for some insight, country gent.

I don't think I spent more than a total of 9 months working in production or a job shop. Did on a few occasions run 1,000 or this or that, but most of my 30-odd years as a machinist were a mixed bag of prototyping, R&D, short run (2 of these and 10 of those), engineering and management.

[country gent]

One of our jobs in the tool room was certifying the production tools and gages. Had to be done once a year on most measuring tools. ( not zeroed but actually certified as accurate measurments) So parts made in one plant fit mting parts made in another plant. MAchinists and tool makers measuring tools see a broader range of use than what they do on a production line where they may measure 100-300 parts a shift ann the same size. very localized wear here...

[smokeywolf]

country gent, isn't it usually the Inspection Dept.'s job to certify the measuring tools? I did a short stint in aerospace and still have a few tools with the Inspection Dept.'s sticker on them.

[country gent]

At Campbells the inspection dept took care of the soup lines and food products, In the can plant the tool room took care of gages and measuring tools. A the last plant (SMall auto parts plant for one of the big three) Gage and lay out checked tools we would rebuild rework as needed the they reverified them.

[Big Boomer]

An old millwright did me a great favor and gave me a 1" Starret Vernier micrometer several years ago. Still in its original black box with instructions and adjustment wrench today and its the one I reach for when I want to know or have to know what the up to 1" dimensions are. I bought one for my old college/shooting bud but he couldn't get the hang of reading a Vernier micrometer. Now I have two just alike though made many, many years apart. Paid $ 125 for the second one. Wouldn't take less than that for it today. Both read exactly together. Really good tools just don't go bad. Big Boomer

[Forrest r]

If you look around test blocks can easily be found. I use this 1/8" set of sweat blocks allot to test my mics and calipers. The standard 1" test rings also work well.

[IMG][/IMG]

I also use different block gauges to test the accuracy of different mics or calipers. The longer blocks do real well when checking the oal of rifle cartridges. If I'm testing a 2.6" oal it good to pull out the 2.5" or 2.75" block and check the calipers for accuracy before measuring a bunch of 308's.

I have some different sized blocks I'm not using. PM me if you might be interested in a couple of them.

[IMG][/IMG]

[w5pv]

Forget the cheaper tools and go with a name brand like Starrett take care of them and they will outlive you.I have Starett tools that have been used for over Sixty years and are still good tools.

[Drew P]

New starret not that great. I think they sold the name a few years back.

[mdi]

Country Gent sounds like he knows what he's talking about. When working as a machinist, to +/- .0005", I would have Inspection check my measuring tools monthly. But for home use, like the last 12 years, my mics have not been used enough to need adjustment/calibration. (FWIW; life long machinist/mechanic I prefer analog, plain old fashioned hash marks on the thimble type mics and dial calipers. I've experienced digital "failures" in the past)...

[country gent]

Zeroing, calibrating and certifying are all actually slightly diffrent things. Zeroing a set of mics needs to be done by the person using them due to afore mentioned feel and eye sight. Calibrating a set of mics is more involved and may require adjusting the threads collet and or the spindles location on the threads. certifying is simply proving thru measuring known oblects ( gage blocks or pins) thru the tools range as accurate thru its range of 0-1 1-2 2-3 or in a calipers 1-6. I am currently using Mitoyo 0-1 digital mics and mitoyo 1-6 digital calipers.

[smokeywolf]

You sure those aren't "0-6" digital calipers?