Micrometer or Vernier?

[Russell James]

Fellas, I am looking at buying a micrometer or vernier, the mikes in Aus are real expensive so would the current range of LCD type calipers be just as accurate.
I have used both before,years ago and the calipers didnt have the readout on them, and were accurate up to about 10 thou, where the mikes if used correctly are spot on. For reading boolit diameters are the calipers accurate enough in comparison to the mikes?
Regards Russell James

[leftiye]

The new digital electronic calipers are supposed to be within a half a thou. Mine actually is. Nowadays they're available at about $ 20 (US) and up. Even the cheap made in China dial calipers I've had (have) are within about one thousandth.

If you can get a mike from over here shipped to you there are mikes in all ranges as to both accuracy, and price. And, they aren't necessarily inaccurate because they aren't expensive. Some of my mikes are the "made in China" ones, and they're cheap, but quite accurate. I've seen "Apprentice" mikes for about $6, I think my first mike was one of these.

I wouldn't say that being off a thousandth would be a disaster when measuring a boolit- especally if the boolit ended up being a thou. too big. But mikes that measure in tenths of a thou are all over the place, and I'd feel mucho mejor about that scenario.

[andrew375]

The choice depends on what level of accuracy and precision you are after. By thier basic design a caliper cannot compare with a micrometer.

Do not get the idea that just because a digital caliper has a display that goes to four decimal places that it is actually capable of that degree of precision. I could produce a plastic rule graduated in hundredths of a millimeter (0.004", appox.) but that wouldn't mean you could reliably measure to that level of precision. Within the mechanical engineering industry calipers are called guessing sticks, for good reason! Don't get me wrong, a caliper is'nt useless for measuring things, just respect the limitations. And as for plastic calipers, don't get me started! :roll:

Micrometers are engineered to give the precision they are calbrated for, that is why they cost more.

DO NOT SKIMP ON COST OF MEASURING EQUIPMENT! Using inaccurate measuring equipment will just result in wasted time, effort and material. If you cannot afford Mitutoyo prices see the Starret line, they were reasonably priced but not lacking in quality. My Starret mics are nearly thirty years old and still within original calibration.

Do not buy second hand measuring equipment unless you know the source and/or it has an up to date calibration certificate. A micrometer that has been used as a gee clamp or adjustable spanner is worthless.

[Buckshot]

...............For reloading and cast boolit purposes a 6" dial caliper (dial guestimator) would be fine. Assuming they are accurate themselves, part of the accuracy also comes from your use of them, just like a mike, ie: how your 'feel' is.

One issue with dial calipers is accuracy over the length of the rack. Run the jaws open to 3" and is that REALLY 3" (or cm's). It's easy enough to check the very basics and that is with some leaf feeler gages. Those'll only get you out to maybe .030" or so, but if your caliper in 'on' for each one of them then you can be at least somewhat assured that they are good enough for the purpose over the length of the rack.

For reloading needs the caliper is the best bang for the buck as you have (normally) a 6" capability. You can measure a 45 cal slug, or the OAL of a complete loaded round of ammo. Basicly anything from .000" to 6.00". With a mike you'd need 6 of'em for the same capacity.

.................Buckshot

[Lee]

How about some techniques and critiques on actual measuring methods?
I set the calipers or mikes just smaller than the diameter of the boolit. Lay the boolit on the gap, then carefully, slowly open up the measuring instrument until the boolit just falls thru of its own weight. I find I can repeat the measurement to within 0.001" that way, and don't have to worry about deforming that which I am measuring............(or am I??)...................Lee:wink:

[versifier]

Older tools aren't necessarily inacurate or outdated, as long as they have been properly cared for. But, knowing the source is definitely a big plus. I have Starret mics, depth mics, and verniers that were made from 1915-1925 that are still spot-on. My great uncle was a toolmaker and taught me young how to use and care for them. I guess he was satisfied I'd learned, because he left them all to me. The modern dial and electronic units are much easier to use, but as to their actual accuracy, the ONLY way to know is to compare measurements with a tool that is known to be accurate. A good (read: accurate) dial caliper is really all you need for reloading, measuring boolit diameters and barrel slugs, etc. If a tool reads in thousandths (.001), and it is proven accurate, then the possible error is +/- .0005. I would not believe a vernier, even an electronic one with a ten thousandths readout, could be realistically expected to give you more than a rough idea of the actual size in thousandths. If you REALLY have to know, then you need a good mic, but unless you are doing actual gunsmithing or machining, that degree of accuracy is unnecessary.

[felix]

Yep, no different than the guns in the closet either. If you REALLY have to know how good YOU can shoot, then you will have to have a modern bench gun to PROVE your capability. ... felix

[leftiye]

Easy enough to know if that cheap caliper (or micrometer) is accurate, but you need some "standards." They all either read zero, or not when closed. Many 1" mikes come with a 1" standard to see if the mike reads 1" when fully open. Gage blocks, etc. can be gotten in several grades,all more accurate than needed for our purposes here, and will provide you with a standard to check your mikes, or calipers at whatever opening you desire. Another way of knowing is to measure something with a tool that you know is accurate, and then see what the tool in question says it measures. The ones that I've seen ( calipers) that were off were off the same amount for the whole travel. The racks were good enough, but they were out of adjustment.

[Russell James]

Thanks fellas, this has helped a lot.Looks like after comparing prices, the best way is to buy from the states.
Regards Russell James

[leftiye]

Another thought: Accurate measuring tools are the standard (nice), and I advocate accurate tools. However, if all of the measuring on a given item is done by the same tool (however inaccurate), it usually works fine as all measurements might be off a smidgin, but they're all off by the same amount and in the same direction- everything fits and has the correct clearances. Indeed take the example where a guy finds out that his mike needs adjustment, and then wonders how the problem remained hidden for so long.

[uscra112]

For checking your mikes and calipers, a selection of commercial solid dowel pins from your local mill supply can be used. These are centerless ground, and tend to run within .0001" of nominal. Your mill supply can also supply "Pin Gages" which are used for checking holes. They are even higher precision - typically within 50 millionths of their nominal size, and remarkably cheap - much cheaper than gage blocks!

The electronic type calipers don't have much accumulated error over their length - the scale is laid down optically, but I find that most of mine develop some shake in the moving jaw, so that the uncertainty is often about .001" at the jaw tips. These require constant checking with the aforementioned reference artifacts if I want to do close work with one. Just closing up and zeroing doesn't mean that they are correct at, say .357". The gear type can have more accumulated error, but seem to be less susceptible to the shake problem. I've never tried to figure out why. If you are loading ammunition, a caliper will be quite good enough, as long as you know how to check it.

When I am making really close parts on my lathes, I do use a mic. My best one is a 40 year old Brown & Sharpe, bought at a yard sale for $15.00 or so.

Harry Pope is said to have carried around the same 0-1/2" mic for 40 years. It certainly must have been worn a little, but doubtless he knew what it's quirks were, and it served him to his satisfaction.

Yes, technique counts for a lot. When we test gaging systems at work, we have to have three different operators use them, so we can see how much error is introduced by technique. Just like shooting - consistent technique counts big!

[Bret4207]

FWIW- A set of feeler gauges can work as a standard. Use one of the heavier ones, .025 maybe. Make sure it's clean and the anvil faces are clean. Try you mic on it and use the same style of measuring you'd use any other time. If you use the ratchet do so when you check it. See where the mic measures and either adjust the mic to be dead on or remember just how much it's off. It's all relative unless you're working off a blueprint or to a plan or specification of some sort. Feelers are lots less expensive than standards and work in a pinch.

[Nardoo]

Russell,

A friend has one of these:

http://cgi.ebay.com.au/OUTSIDE-PRECISION-MICROMETER-0-TO-1-INCH-TAX-INVOICE_W0QQitemZ140141716022QQihZ004QQcategoryZ20 766QQrdZ1QQcmdZViewItem

It seems to be as accurate as my old English Moore & Wright. And that price is good.

Heed the warnings of purchasing used. I remember years ago at school seeing the metal work teacher go ballistic when he found one of the kids draw filing his model that was clamped to the work bench with two micrometers. I guess they looked like fancy little G clamps!

Nardoo

[floodgate]

Nardoo:

A friend, Rudi Prusok in MI (Archivist for the ASSRA), wanted to shake up his buddies at the Beeson range; I had mentioned getting a couple of 2" - 3" Chinese micrometers for less than $10.00 each along with a bunch of "bargain" stuff, and he asked to borrow them. Used them to clamp his spotting scope to the bench, and got a howl of outrage from some, and laughter from others. I checked them after he sent them back, and the calibration vs. the standard was not hurt a bit.

floodgate

[Hairtrigger]

Get a vernier calipers. Your friends won't borrow it since they won't know how to use it!
I used to set up CNC routers and had a brand new digital calipers get stolen by an employee of a customer. I purchased a good vernier calipers and used it for the rest of the time I had the job.

[codarnall]

Fellas, I am looking at buying a micrometer or vernier, the mikes in Aus are real expensive so would the current range of LCD type calipers be just as accurate.
I have used both before,years ago and the calipers didnt have the readout on them, and were accurate up to about 10 thou, where the mikes if used correctly are spot on. For reading boolit diameters are the calipers accurate enough in comparison to the mikes?
Regards Russell James

Try www.harborfreight.com they have lcd calipers from $7. to $20 which are more that adequate for miking slugs. In fact they have just about any Chinese gadget. They (China) haven't quite taken over yet so get them while you can.