Calipers vs micrometers

[Rockchucker]

I know micrometers are suppose to be more accurate than calipers, but if I have a digital caliper that reads to 10 thousands why wouldn't that be as accurate as a micrometer. I need to make an accurate reading and don't have access to a micrometer and buying one sounds very expensive.

[white eagle]

its the design of the instrument

[Longwood]

One way to understand how different a mike is compared to calilipers.
A caliper will measure fairly accuratelyt, one thousandth which is the thickness of the cellophane on a cigarette pack and a Mike will accurately measure one tenth of that.
Some will do even better.
Cheap mikes vary for several reasons so each time you measure something, it can read different.

[cbrick]

It's the nature of the beast and what they are designed for and intended to do. In a machine shop if knowing within .001" is plenty good they grab the calipers. When they really, really need to KNOW they grab a micrometer.

Rick

[Shiloh]

I'm with white eagle on this one.

I have many calipers and only one mike. The mike is for precise measurements. Calipers on my various reloading areas, my stone setting bench and my workbenches.

Shiloh

[Rockchucker]

Thanks for the reply guys, looks like I'm in the market for a micrometer. I'm not in the market for a professional series, but one that would give me accurate readings. Would a set from Sears or an auto parts store give me the accuracy I'm looking for. I just want to measure my bullets made from my alloy and be able to know what the exact size is. Guess my expensive digital calibers won't do that. Thanks /Ron

[RayinNH]

You said you need to make an accurate reading. An would lead me to think one. You also didn't say what you were measuring either. If only one use the caliper or if a really important measure go to your local machine shop and let them measure it for you. Probably wouldn't charge you either.

If your measuring a bore slug, needing to know to the nearest .0001 isn't necessary when you'll be loading a boolit that is .002-.003 oversize anyway...Ray

[Rockchucker]

I need a .4520 boolit, anything smaller gives me a little lead to clean up after shooting. My sizer die is a marked .452, my caliper says its dropping 4500 to a .4510, my alloy.calipers or the die may be my problem. I'm just trying to work it out with my 50% ww/50% pure lead/2%approx tin.I'd like to get a mike reading on this boolit before I start honing the die.

[Echo]

Reliability is the name of the game in measurement, whether we are talking about mikes, calipers, IQ tests, BP, &cetera. If the device is repeatable, that is, gives the same results time after time measuring the same dimension, then it is a reliable device. Validity is another thing - does the device really measure what it is being used for? A steel tape is a very reliable measurement tool, but one should not use it to measure intelligence. So.
If we have a reliable caliper, that is, one that gives the same value every time it is used on the same item, then we can have a lot of faith in that measurement. It may not be exact (nothing is - always a tolerance), but in relation to all the measurements made by that particular caliper in the past, the current reading relates strongly to to actual dimension. If the caliper has been calibrated, and the jaws kept clean - why not?
But reliability is the key factor.
Example - we slug a barrel, and measure with calipers, and find the groove diameter is .308. We use the same caliper and find the boolit diameter is .309. We are happy campers. What difference does it make if the actual diameters are .3078 and .3091. I don't believe our discipline REALLY needs to know that. On the other hand, if the calipers were cheap, made 40 years ago in Bangladesh on mule-powered machinery, we might get a value of .309 on the boolit - then when we went back and measured again we got a reading of .310. Wondering, we would try again (same boolit), and get a reading of .308. THAT caliper is unreliable, and should be used as a paper-weight. No reliability means no validity.

And Yes, I did teach this stuff at one time.

[Echo]

I need a .4520 boolit, anything smaller gives me a little lead to clean up after shooting. My sizer die is a marked .452, my caliper says its dropping 4500 to a .4510, my alloy.calipers or the die may be my problem. I'm just trying to work it out with my 50% ww/50% pure lead/2%approx tin.I'd like to get a mike reading on this boolit before I start honing the die.

I trust your calipers. Just because the die is marked.452 doesn't mean boolits come out @ .452. But.
Do those booits that measure .451 lead your pistola? How did you measure the .452 boolits that didn't lead?

[MBTcustom]

I am a machinist. I buy only the best dial calipers and I know how to use them (ie. I have the "touch") I trust my measurements with a dial caliper to .0005 or +- .00025. Digital calipers lie thats all there is to it. I cant trust them any closer than .0015 or +- .0007 no matter how expensive they are. Micrometers, on the other hand render accurate readings less than .0002 with the cheapest set harbor freight sells, and I trust my good set to be accurate within .00005 all day long (as long as I dont hold them too long and warm them up in my hand.
If you can consistently measure a cylindrical surface of known diameter within .001 with calipers, consider yourself a very talented hand with your tools. (it doesn't matter what the dial reads you know, with digital calipers that seems to have little bearing on what you are actually measuring.) However, with a micrometer, using the friction thimble or ratchet, anyone can be expected to measure to .0001 and be reasonably sure that the object is within .0004 of that reading. That's just the way it is.

[uscra112]

Having spent a lifetime in metrology qualifies me to point out the accuracy and the precision of an instrument are two different things. Just because an instrument reads to four digits doesn't mean it's that accurate, or anywhere near.

The caliper in particular is subject to errors that a micrometer is not, particularly the parallelism of it's jaws, which are imperfectly controlled by the slide. Look up "Abbe error" for a detailed description. (Named for Ernst Abbe, the man who made metrology a science.)

An old, old rule of thumb in metrology is that the instrument you use should be ten times more accurate than the degree of the measurement. i.e. if you want to know the dimension in thousandths, the instrument should not only read-out in "tenths", it should be accurate to "tenths". A properly adjusted "tenths" micrometer, properly used, will be both accurate and precise to .0001", while a caliper is rarely even as good as .0005", no matter how good or how well handled it is.

Cheap calipers suffer much more from slide errors than good ones do. I'd select a name brand caliper. I do have one caliper - a Mitutoyo - for "quick and dirty"measurement. Anything less is a woodworker's tool.

Cheap micrometers can actually do OK, but a well-finished one is much more satisfying to use. Do not buy from Sears or an auto parts store. Neither sell high-grade instruments, in my experience. Go on evilBay and buy a Mitutoyo, a Fowler, or a Starret. I tend to buy Fowler, because they are a less-well-known brand and prices are less, but my "Lord Chancellor" is still a WW2-era Brown & Sharpe. (I don't recommend them anymore because they are tricky to adjust, but they were top-notch instruments.)

Digital mikes are much easier to read quickly, so the mike that lives next to my lathe is a Fowler "mechanical digital" model. I still have to read a vernier for "tenths", but it needs no battery, which pleases me no end. Some older Fowlers are actually Swiss, and are jewels. This one cost me $30.00 including shipping on evilBay.

[KYCaster]

I agree with Echo.....and add........

Accurate measurements depend as much on proper and repeatable technique as they do on the quality of the instrument.

If you buy an economy priced micrometer you won't have any more confidence in your measurements than you do with your expensive caliper.

Jerry

[GRUMPA]

Calipers are only good for REFERENCE nothing more nothing less. When you want to know the true size of anything that's where Micrometers work best. Being a precision grinder and handloader/reloader or whatever if I can't get a measurement to the .0001 I aint happy, and yes I do own things that will go to .00005. Totally overboard on some things but I do use it occasionally but it's a choice at least is up to me and not my equipment.

Pressure applied to Calipers can and will give the user a plus or minus .001 difference on average. With what I've done in the past I have to be able to have an accuracy range of no more than .0001. If I'm going through all the trouble to melt and mix lead size and lube assemble a round for an error factor of plus or minus .001, it isn't going to happen.

Basically I'm the one that's going to be in control of what I'm doing, not a piece of equipment that can give me a .002 difference in size depending on how much pressure is applied to it.

Then owning a pair of Micrometers is one thing, calibrating it is another animal all together. Don't think screwing the thimble down so the anvils touch each other and getting a "ZERO" reading is OK, it isn't. Anvils aren't always parallel with each other and requires something like a known size ball bearing and checking it at different points on the anvils.

[Mal Paso]

My everyday Micrometers are Harbor Freight. On sale a set of 3 ( up to 3" ) with 1" & 2" Standards for Calibration is $30. Just checked the 1" against my US ones and they are all within .0001

Just checked my, just bought, $16 on sale with cupon Stainless Dial 6" Caliper from HF It's dead on at 1". Looks to be the same model everyone else is selling for $30+

[Rockchucker]

How did you measure the .452 boolits that didn't lead?

With a digital 35.00 set of digital calipers and a 25.00 set of analog dial calipers.
I know I'm no machinist, or a teacher, But I am a student here learning what I can from the people with the knowledge I'm seeking. The above posts could not have said any better by anyone else. I hope more people chime in here so more of us have a better understanding of measurements. Looks like I'm in the market for some quality instruments.

[GRUMPA]

How did you measure the .452 boolits that didn't lead?



Your going to have to explain that one, that question has me stumped, well that or I didn't have enough coffee yet :coffeecom

[geargnasher]

I think the number-one issue with digital calipers is that laymen think just because it reads to four decimal places it must be accurate to four, or at least three. Not so. If you have checked them against a standard, you can pretty much count on them being +/- .0005, even the good ones. Machinists call Vernier calipers "very-nears" for a reason.

USCRA112's reference to the wood shop cracked me up, I've said that before! Calipers for the wood shop, micrometers for the reloading room, and of course only micrometers for the garage.

Gear

[Recluse]

This is making my head hurt. . .

Quite honestly, I've found in four decades of reloading that I have yet to have occasion to need to measure anything on a boolit, bullet, case, neck, primer, flake of powder, nose-booger, hair follicle or anything else that has ever landed on my reloading bench to within .0000anything of an inch.

In fact, I went twenty-something years before I even had a pair of calipers on the bench. Granted, once I got a set, I wondered how I'd lived and loaded without them for so long. . . but my old targets, dead animals and shooting trophies never seemed to wonder about that.

A micrometer IS useful for the handloader and especially the boolit caster. No doubt. But I've yet to see the bore, brass/neck, and lead boolit combination in which .00001 precision would make any visible, noticeable difference in much of anything.

To Rockchucker--go shopping on Ebay or at your local pawn shop. As long as you can consistently measure to .0001, you're fine. Even THAT is often overkill for lead boolits and the bores for which we discharge them from, but you can get that fourth spot over from the decimal point for basically no extra money, so go far it.

I have a Fowler mic that I gave $40 for, and a Mitutoyo that I gave $30 for--both on Ebay. That Mit is one smooooooth working piece of machinery.

But again, somehow I lived without calipers and micrometers doing this stuff and still managed to do okay. They are tools that are useful, not mandatory.

:coffee:


:coffee:

[uscra112]

Using hand-held gages, technique is everything. If you have the time and interest, look up "gage repeatability and reproducibility study". The "ANOVA" protocol used in the Western world defines how to gather data and how to mathematically reduce it to a simple statement of the variance of a gage. (It says nothing about accuracy.) Understanding variance has been a part of metrology science for many, many years. The causes of variance for most measuring instruments are pretty well understood, and the human factor is by far the biggest source. This is one big reason why auto engine plants use coordinate measuring machines as much as they do, even though they're often much slower than hand-held gages.

Lastly, (no offense to Recluse) the thing about not having good measuring instruments is that you don't know what you don't know. Having spent 15 years bringing the Detroit 3 into the 21st century, I can relate tale after tale of how we found "bugs" in their machining processes that were creating massive warranty headaches for them, and about which they knew nothing because their gage methods could not detect the errors.

[stubshaft]

Recluse's thoughts mirror my own with only one caveat, and that is I want to KNOW what something measures at not guess.

[Wolfer]

What Recluse said!
I also went for years without calipers or a mic and made it ok.
That being said I now have two of each that I use all the time. The mics are from grizzly and harbor freight, both for around six bucks each at the time. The calipers are from midway and grizzly. With a little practice I can get them all to read pretty close on the same object like a jacketed bullet.

These are not good enough for a machinist but for a hobby reloader they work just fine. For instance if I measure a bore slug at 308 and a sized boolit at 309 with the same caliper several times I can be pretty sure my boolit is bigger than my bore regardless of what size they truly are.

In the past I could push a boolit through my cylinders and tell whether they were big enough without having a real clue as to what size they really were

[303Guy]

I've just been measuring boolits with a digital caliper and comparing it to a digital micrometer. I'd conclude one cannot measure lead or paper accurately with a caliper - not even reasonably. The measured medium compresses under the jaws, meaning the result is always less than actual. Another problem with the caliper is getting the boolit perfectly square in the jaws.

[Longwood]

I need to make a powder thru flaring die.
I "Will" use a micrometer.

[fredj338]

My buddy is a machinist, he usues micrometers for serious measuring & calipers for rough 0.001" measuring. Most reloading/casting, calipers are fine. You'll never get lead bulelts to 0.0005" dia, too many variables in mold size, die size, alloy, temps, aging, etc.

[RayinNH]

How did you measure the .452 boolits that didn't lead?

With a digital 35.00 set of digital calipers and a 25.00 set of analog dial calipers.
I know I'm no machinist, or a teacher, But I am a student here learning what I can from the people with the knowledge I'm seeking. The above posts could not have said any better by anyone else. I hope more people chime in here so more of us have a better understanding of measurements. Looks like I'm in the market for some quality instruments.

Did both instruments give you the same dimension? If they did, they're probably fine for your needs. Change alloy and you may get the .452 marked on the die. If your going to stick with that alloy you'll probably need to hone the die.

As Echo said it really doesn't matter what the instrument reads as long as it's repeatable for your uses...Ray

[brotherdarrell]

I have a cheap set of calipers that "consistantly" measure +.001" actual measurment, but I know that and take that into account anytime I reference the caliper. It is not "accurate" but it is "consistant". I have a cheap micrometer that is "in-cosistant" if I vary my technique at all. With a "consistant" technique it is "accurate". I am trying to upgrade both, with a mic being first priority. Do I need either? Probobly not, but I want both.

In the same vein, I am on my third 'cheap' digital scale. Is it "accurate"? I don't know, but it will give me the same weight for the same item each and every time, so it is "consistant".

brotherdarrell

[GaryN]

If you watch fleabay you can buy Mitutoyo micrometers all day long for around twenty dollars. They are used but generally you can read the add and look at the pictures and tell if it is a good one. There are a lot of college students that use them for a class and then sell them.

[mpmarty]

I have both calipers and micrometers. One caliper is vernier and one is digital. The mikes are one old Starret and a new digital/vernier for tenths. I use calipers to measure overall cartridge length and micrometer for boolit diameter and other stuff under an inch in size.