Digital Calipers - 2 vs 3 decimal places

[cdnredneck_t3]

Well Legendboy and myself are on the same page.

I am a Millwright. I trust a Vernier MIC if I am doing my own measurements like bearing clearances and what not. But when I take a measurement for a coupling and want 2 to 7 tenths interference that is where the tolerance comes in. My MIC and the Machine shops could be off a tad from each other. Who is to say which one is correct depending on ambient conditions. The shaft could measure different in my shop compared to theirs. If my shop is 28 C in summer and the Machine shop is 19 C but their MIC was on the lathe and a little warmer..... When measuring to the tenth there are so many variables that there is no way to be certain you are bang on.

 

[07blackwater]

Nice collection of instruments legendboy.

 

[blacksmithden]

Well Legendboy and myself are on the same page.

I am a Millwright. I trust a Vernier MIC if I am doing my own measurements like bearing clearances and what not. But when I take a measurement for a coupling and want 2 to 7 tenths interference that is where the tolerance comes in. My MIC and the Machine shops could be off a tad from each other. Who is to say which one is correct depending on ambient conditions. The shaft could measure different in my shop compared to theirs. If my shop is 28 C in summer and the Machine shop is 19 C but their MIC was on the lathe and a little warmer..... When measuring to the tenth there are so many variables that there is no way to be certain you are bang on.

Thank you !!!! I'm glad there are still other people out there that understand the difference between a drawing board world and the real world.

If you had a set of gauge blocks at a set temperature on both ends (your shop and the machine shop)....you had the same micrometer, same barometric pressure, same humidity.....you calibrated the mic.....blah blah blah.....in other words, laboratory conditions....then yes, you could say with some certainty that your readings are spot on. In the real world, it just doesn't get that accurate.

 

[07blackwater]

I dunno, if my vernier's are zero'd when there closed that's good enough for anything I need to measure.

 

[trevj]

Thanks for the thoughts guys. I only wanted digital cos I can't see the regular ones. I'm pretty sure I can learn how to read the regular vernier. Problem is, I could hardly see the numbers!

Time to spring the $40 or so for an Opti-Visor or less than that for a cheapo set of reading glasses.

I've been wearing glasses since the eighth grade (a long time) and not seeing clearly is a real irritant to me! I'm nearsighted, and still find that magnification helps for some stuff.

Nothing wrong with calipers for non-critical measuring, esp if you have a way to check them against a known accurate measurement that is somewhere near the dimension you are working with. In a shop, that would be against a setting standard or gage block stack, at home, settle for playing with the calipers until you get the same reading repeatably, without looking at the measurement while you are setting it. It may not be dead nuts right, but it will at least be consistent and same. Same is good! If you need "right" buy some gear that will measure "right". Keep in mind that the reloading companies will happily sell you a Chinese made digital caliper as a 'precision' measuring tool, so that gives you some idea of the accuracy levels they feel are lawyer-proof.

Pretty much any caliper you use will tell you more info than one of the case length gages that the reloading companies sell.

Cheers
Trev

 

[Meph]

you don't use calipers to measure critical dimensions less then +- 0.005

Yes, that includes my $275 dollar mitutoyo digital "half thou" reading calipers. For you to say you can read tenths with a caliper is just f$#king stupid lol


IF you ever need to measure to half a thou (doubtful) you will want to use a micrometer (or surface reading indicator setup; grinding?) . I have a nice mitutoyo 0-1 digital mic that claims to measure to 0.00005 (1/000005 that I trust to measure to 0.0005 lol.)

Beyond that, ccm or a comparator. neither of which i have (or need)

To the OP, if you want to accurately to one thou on an OD, grab a decent quality mic, kar is quite reasonable.

Not saying you can read ten-thous on a caliper, I'm saying at 21C, a good caliper is ACCURATE to plus or minus 5 ten-thou. Not "READABLE" to 5 ten-thous, stop putting words in my mouth. So I'll be generally on the ONE THOUSANDTH. You're saying "measure critical dimensions less then +- 0.005" that means if you measure a 1" piece, you will accept readings of 1.005" to 0.995". That's a full ten one-thousandth (0.01) of tolerance, and unless you're in a bad situation, there's not much of a way that it's that inaccurate.

And yes, I'm talking about pretty controlled conditions, and I can be pretty certain they're very close. Again, caliper is generally on the thou, MIC is generally on the ten-thou. That's for controlled conditions for both part and instrument.

 

[cdnredneck_t3]

Not saying you can read ten-thous on a caliper, I'm saying at 21C, a good caliper is ACCURATE to plus or minus 5 ten-thou. Not "READABLE" to 5 ten-thous, stop putting words in my mouth. So I'll be generally on the ONE THOUSANDTH. You're saying "measure critical dimensions less then +- 0.005" that means if you measure a 1" piece, you will accept readings of 1.005" to 0.995". That's a full ten one-thousandth (0.01) of tolerance, and unless you're in a bad situation, there's not much of a way that it's that inaccurate.

And yes, I'm talking about pretty controlled conditions, and I can be pretty certain they're very close. Again, caliper is generally on the thou, MIC is generally on the ten-thou. That's for controlled conditions for both part and instrument.

When you say "MIC" what kind of MIC are you talking about. An exact model would help. And I totally agree with legendboy. If I am Machining a bushing driver or taking the threads out of a fitting so it will slip over a pipe a Caliper is fine. If I am off a few thou no big deal. Even ten thou would not matter. If I am Machining a pump wear ring for the case to match the impeller I use an outside MIC and an inside MIC. That will be good to the nearest thou. That is also where my machining capabilities end. When I am taking bearing fit/clearance checks or coupling interference checks I use a Vernier MIC. Now I can go down to the nearest couple of tenths. I do not use a caliper for anything more than rough work.

 

[Meph]

When you say "MIC" what kind of MIC are you talking about. An exact model would help. And I totally agree with legendboy. If I am Machining a bushing driver or taking the threads out of a fitting so it will slip over a pipe a Caliper is fine. If I am off a few thou no big deal. Even ten thou would not matter. If I am Machining a pump wear ring for the case to match the impeller I use an outside MIC and an inside MIC. That will be good to the nearest thou. That is also where my machining capabilities end. When I am taking bearing fit/clearance checks or coupling interference checks I use a Vernier MIC. Now I can go down to the nearest couple of tenths. I do not use a caliper for anything more than rough work.

This is what I work with, usually, exact same micrometer as the one you see here. Mostly do outer measurements, controlled conditions, and they're one the money. Our practical exams had parts to measure with vernier micrometers, vernier calipers, and we had one point deducted from each thou that was off for the calipers and one point deducted for each ten-thou that was off for micrometers. We had to calibrate the micrometers on our own, and it was for hardened, ground then polished pieces.

Again, my situation is different from yours - you seem to be more in the production and less in development/prototype work.

 

[Shrek]

Well Legendboy and myself are on the same page.

I am a Millwright. I trust a Vernier MIC if I am doing my own measurements like bearing clearances and what not. But when I take a measurement for a coupling and want 2 to 7 tenths interference that is where the tolerance comes in. My MIC and the Machine shops could be off a tad from each other. Who is to say which one is correct depending on ambient conditions. The shaft could measure different in my shop compared to theirs. If my shop is 28 C in summer and the Machine shop is 19 C but their MIC was on the lathe and a little warmer..... When measuring to the tenth there are so many variables that there is no way to be certain you are bang on.

Yep, we used to go through the same process. It always payed to measure the coupler and then measure the shaft regardless of what was ordered or what it was supposed to be.

We used to get vernier's for free (the plastic ones) and lots of the guys would keep them in their coverall pocket........never saw them get used or trusted for more than stirring coffee though!

 

[HKMark23]

I have both 2 and 3 digit verniers. I don't use the 2 digit ones much. Your trimmer will be capable of adjustments down to a couple of thou at least and a 2 digit vernier is useless for detecting such differences. Accuracy beyond 3 digits is an unwarranted expense unless you've got tools that adjust to 1/10,000 or better. The reloading tools you're likely to buy just aren't capable of this.

If you feel you need better, go to a micrometer, as suggested above, but I personally think that beyond the 3 digit vernier, money is better spent on a concentricity gauge setup like the one RCBS sells. You'll use it more.

 

[cdnredneck_t3]

This is what I work with, usually, exact same micrometer as the one you see here. Mostly do outer measurements, controlled conditions, and they're one the money. Our practical exams had parts to measure with vernier micrometers, vernier calipers, and we had one point deducted from each thou that was off for the calipers and one point deducted for each ten-thou that was off for micrometers. We had to calibrate the micrometers on our own, and it was for hardened, ground then polished pieces.

Again, my situation is different from yours - you seem to be more in the production and less in development/prototype work.

The MIC you have pictured is only good to a thou. Do you have MIC's with this scale?

I am just asking because you use the term "MIC" for everything. To me your MIC is a MIC and the one I posted is a Vernier MIC.

 

[Meph]

The MIC you have pictured is only good to a thou. Do you have MIC's with this scale?

I am just asking because you use the term "MIC" for everything. To me your MIC is a MIC and the one I posted is a Vernier MIC.

Yes, the scale you have posted is the one on our vernier MIC. They look a lot alike...

 

[warrenb]

**I just noticed I'm an official 'regular member' now, I'm so proud!**

Congratulations! Continue to post at a similar rate and in 4 or 5 years you too, like myself, will join the elite ranks of Big Mouths. The feeling of superiority cannot be described.

Now what was this thread about again?