Different Types of Micrometers

Here's a little show and tell of some of the different types of micrometers that I own. I talk about how and when they're used and some of the quirks of each type.

[@turningpoint6643]

I'm in 100% agreement about studying what's in the tool and individual tool manufacturers catalogs. I picked up a great deal that way. Mitutoyo and Starrett have good videos here on YT about how to best read and use there metrology equipment. Even with something as simple as dial or digital calipers it seems about 90% don't use them correctly to get the best from the tool. I'd also add that with thread mikes having a trustworthy set of precision thread wires is a good way to double check that your thread mikes are at least in the ball park of what they should be. And used sets of depth mikes are something that really shouldn't be fully trusted without that check for each rod against that stack of gauge blocks. It's too easy for the previous user that might have "adjusted" them to what they think is correct. Going by what I see on the forums and quite a few on YT, but mostly non machinist related channels you should do an in depth video about repeatable accuracy verses a measuring tools resolution and throw in some details about uncertainty of measurement. I've seen lot's who think that last 5/10ths digit on a dirt cheap digital calipers screen actually means something.

[@aceroadholder2185]

Turning Point, the last 5/10ths digit does mean something on digital calipers, no matter who made them... its just that the last digit isn't giving you the actual size of the measurement, only the range of what it might be. Digital measuring devices are an all or nothing proposition in the last digit. This means that a digital caliper whose last digit is either "0" or "5" can't detect any variation closer than +/- 0.00025" . As a practical matter for anything whose size needs to be determined any closer than +/- 0.005" , you shouldn't be using a caliper of any kind.. that's what a micrometer is for. There are often circumstances where you can't use the micrometers you have and you can get away using digital calipers zeroed against gage blocks or a known size to get within +/-0.001" pretty reliably. Cheers from NC/USA

[@turningpoint6643]

@@aceroadholder2185 I should have clarified my statement instead of being lazy and shortening it up. Unfortunately this is gonna get long. I'm sure you already know all this but others might not. I agree with your points about how the numbers are displayed. They match with everything I've read about how they work. For any of the decent digital calipers I've seen or used. The manufacturer has to follow the industry standard for metrology equipment and there made well enough to be accurate to + - one count and can then pass the QC checks. I've tested enough metrology items such as digital mikes to know the higher end equipment has been repeatable to usually a bit better than that on gauge blocks, but the + - numbers are still the maximum allowable deviations while falling within tolerance and would still be considered as accurate. So some tools will also be at those upper limits of what's allowed. Without checking it's another unknown. Most of what I have checked hits around half the allowed, one or two have been about 75% of the allowed. As you say, under .005" then break out the mikes. The main difference even if the internal electronic measurement & reading systems were equal is the mikes have an in line close tolerance mechanical system with a very rigid frame. Calipers have minor but important clearances that without them the calipers jaw couldn't move. Those allow it to tilt a very minor amount in each direction on the calipers beam. Due to the design that clearance is greatly magnified along the jaw tip. So a calipers mechanical design is a far less rigid and repeatable system than a mike has. Even it's shape and length is against it for possible thermal changes just by holding them long enough. Like you I've proven to myself that I can get dependable and repeatable readings with my Mit's on those gauge blocks, but only under the best of conditions, taking my time and using good technique. That proves how your doing it and the tool is accurate and repeatable to a low limit. So those are ideal conditions and that's still a possible 1 thou in each direction and a long ways from 5/10ths. Everyone knows measuring parts in a chuck or vise is never ideal and the surfaces being measured sure won't be of gauge block quality when machining metal. Since the equipment can't repeat to 10ths or even be 100% trusted as being within an exact thou there's uncertainty and the display of that last 5/10ths digit as I said really does mean nothing about the actual measured size your shooting for. Yes the calipers are reading a rounded off jaw position change to that displayed number, they might due to random luck even be quite accurate once in awhile against what it's measuring. But that display can only show the current jaw position and not how well they fit and touch against the surfaces your trying to measure. That's another possible source of error. So the calipers built in mechanical design issues, and the parts actual size would almost never agree within that 5/10ths accuracy. The number is pointless to think it means anything as far as what your trying to measure. At best it's an indicator that you might be a bit under or over the thou digit, or maybe your really a full thou away from the display reading. I just ignore it on my mits and still won't trust that last thou digit enough that I'd bet money on that number always being correct. Throw in those less than ideal shop conditions, thermal effects, variable user pressure on the moving jaw to name just a few and those add even more variables. They may or may not partially cancel themselves out, so it's only logical that if it has to be measured and known to be accurate to under your .005" then yeah a caliper isn't the tool to use just as you say. They'll get you close enough to then use a mike, or for some parts that close is good enough. To expand a bit on some of the videos I've seen on YT and why I mentioned that 5/10ths digit. Some will quote that number like it's written in stone. One in particular was measuring lead .22 bullets. I'm extremely doubtful my Mit digital mikes could measure a coated lead bullet to an accurate 1/2 thou. Sure the mike will do better than that, the swaged surface and material type still isn't good enough to do so with any real confidence in the numbers your seeing. Try that using a 15 buck off shore set of calipers used by someone who obviously had little experience? I do get and understand why someone like the bullet guy would think the display numbers are the tools actual accuracy. But it just ain't so. :-) I'm no different and used to think the same until I started to pay attention to some of the free information about general shop measurement that's out there. Accurate measurement to low limits with even good calipers is a whole lot more complex and much tougher than it looks.

[@johnstrange6799]

I need to pick up a thread mic one of these days. The tubing mic seems handy too, and of course the depth mic would see plenty of use as well. Thanks.

[@jackdaniels7913]

Just wanted to say thank you for your time and effort its appreciated more than you think! 🥃cheers🍻

[@aceroadholder2185]

The other Vee type micrometers are for measuring 5 and 7 flute reamers. If you do cutter grinder work they are a must-have along with the Vee micrometer for 3 fluted cutters. Tool makers like Starrett often made (and still make) specialty micrometers not shown in the catalog. If you keep an eye out you will run into them once in a while. E.g. I have a Starrett thread micrometer that is made for 55deg. Whitworth threads that I use when chasing Whitworth threads on the lathe. Usually l use it like the comparator micrometer shown in the video and check the work against a known good thread. Cheers from NC/USA

[@StuartdeHaro]

Thanks for the insight. Very cool info!

[@frogdavw9699]

Thanks for an interesting video. Love your tip to let your finger slide on the smooth part of the barrel. I am going to start doing it that way as well

[@chrisstephens6673]

The vee anvil mics are useful for measuring the out of roundness of "precision " ground silver steel (what you call drill rod) it maybe constant diameter but is often not round. Disc mics are often called "paper" mics as they spread the load when measuring softer materials. Did you see my black and white toothy friend? ATB c

[@felixf5211]

I like micrometers and have way more than I need. A collection of sorts, I guess. They all get used. I also prefer a friction spindle. That was a great tip about getting a feel for what's tight - when the fingers slip, it's tight. Wish I heard that before spending a considerable amount of free time with mics and gage blocks. All this being said, just popped a bid in yet another micrometer. Is that so wrong?

[@StuartdeHaro]

Not wrong at all. I want to buy a disc micrometer really badly, but I keep reminding myself that I don't really need it. I just WANT IT!

[@ChessClockCentral]

Great content on your channel. New subscriber here. Thanks for making these videos.

[@kentuckytrapper780]

Good info, thanks

[@geoffreyward4743]

if you have the urge to buy a thread micrometer ,search ------Thread Outside Micrometer 0-25MM with 5set ANVILS------in australia .about $75us