My thinking also. Andrew beat me to it!

It does say 0 – 1" just above the Steinmeyer label

Regards

Edited By Mike Hurley on 21/11/2021 10:17:12

It's a vernier scale, have a look at this link to see an example. They're read by scanning the graduations to find an alignment and doing an addition. The example is metric, which makes for easy reading, but decade inches are just as good. Inch fraction verniers exist too; nasty! Verniers have to be practised and it's easy to misread them. Take care.

Sorry to rain on your parade, but whether or not you have a good buy is unknown. To measure to thou and tenths, you have to prove the instrument reads correctly across its full range. It won't if the internal thread is worn or the anvils are damaged, or the clutch is bad.

Accuracy doesn't matter if the micrometer is only used for rough amateur measuring, but don't assume it really reads tenths! Paying to have the micrometer recalibrated is one option, otherwise check it with Gauge Blocks.

Just an observation: it's not difficult to work to about 1 thou / 0.02mm in a home workshop with the sort of tools Model Engineers own. And that level of accuracy is more than good enough for most purposes. In contrast, getting genuine tenths accuracy is hard work.

Being a suspicious old Hector, I suspect it's rarely achieved at home, and certainly not with un-calibrated second-hand micrometers. As getting good results out of a new instrument requires a fair amount of practice, I wonder how many amateurs really get consistent high accuracy results by measuring? It's not how I work: I measure to get 'close enough', 0.02mm, and then fit as necessary. Fitting is done by using one part as a gauge and comparing: I don't know or care what the exact size is. I'm not making jigs, gauges or turbine blades!

Does anyone really work to tenths, and if so what for? How is that level of accuracy achieved across an assembly? Have the measurements been confirmed by someone else?

Dave

Steinmeyer are still in business and there is a UK rep – link below

They may be able to help with a manual or operating instructions.

https://www.steinmeyer.com/en/steinmeyer/contact/international-sales-representatives/?tx_nwaddresses_addresses%5Bcountry%5D=74&cHash=a11af10c43c9ca4c2ecb0a8a1aa3578f

Hi, well it looks to me that the 8 at the extreme right is in line with the 7 to the left of it, Therefore I think it is reading 0.187.6" But of course I might be totally wrong.

Regards Nick.

Need to be cautious using twist drills to check measurements. Quality drills often have a shank that is a few tenths to a thou or more undersize. ideal would be to use a gauge block, or at least silver steel/gauge plate.

Andrew

As Chris says.Beware of delusions of accuracy!

Even if an instrument reads to 1/10000 of an inch, that is only really accurate under calibration conditions, which usually implies 20'C.

This why Standards Rooms and Calibration Rooms are temperature and humidity controlled, and items are only measured after they have been in those conditions for at least 24 hours.. If they are checking gauge blocks, or measuring instruments for accuracy (To determine if the item should be downgraded from "Standard" to "Inspection" or even "Workshop"

They really are looking for 100ths or 1,000ths of a thou!

Look at the sort of 6" rule that we use. Most are marked "At 20'C"

Depart from that temperature and your "Inch" may be larger or smaller, in absolute terms.

The instrument may read "accurately" when checked against gauge blocks (slips ) if both are at the same temperature, but that does not mean that the measurement IS that, relative to a national; standard..

Just that the instrument is indicating the same as the gauge block used to check it, at THAT temperature. (Whether both are fresh out of a night in the freezer, or a pot of boiling water! )

For most of what we do the temperature does not need to be so accurately controlled, just that the piston is 0.499" to fit into the 0.500" bore. to function as intended..

As an example, a vehicle engine piston may be picked up, and the gudgeon pin is immoveable in the piston. Hold the piston in your hand for a few minutes, and the pin will fall out!

A sense of proportion and fitness for purpose are useful allies!

Howard

Martin,

Fitting bearings has always been a bit hit and miss for me, in fact I have that very job coming up again shortly for the Radford Thread Milling attachment which requires four ball races and a thrust bearing fitting for the worm-shaft. I may have been lucky on a couple of previous occasions when I have measured the diameter of the bore of the bearing recess using a telescopic gauge and micrometer. I made the recess the same diameter as the bearing outer ring, leaving it on the small side, and pressed the bearing in using the vice although I was very careful and conscious that I may crack the casting, so I needed to feel the bearing seating properly without too much pressure but with sufficient resistance to prevent it rotating in the recess. I have used the same 'feel' for the fit of the bearings on a shaft but I admit it is a little 'hit and miss' and is where the cylindrical grinder comes in for sizing the shafts a little more accurately than in the lathe. I am not a trained metal-worker, although I did receive some professional training on lathe work during a later abandoned apprenticeship in the 1960's, so I have to do the best I can which I suspect is the case for the majority of amateur back-shed workers. Of course, I will only get one chance to fit the four bearings as I cannot obtain another casting, so if it goes a bit pear-shaped I will have to resort to the Loctite. Fingers crossed!

Edited By Chris Crew on 21/11/2021 22:55:44

This problem could easily be sorted by the OP – cut a bar in slightly descending increments and use the practical experience of taking measurements to determine the larger incremental changes first and later sort out the finest of diameter changes (after the use of some emery to remove the odd tenths?).

Maybe. The easiest way to find out is to experiment. Get some drills and measure a few shank diameters. Drill shanks aren't accurate, but they're close enough to show how the vernier is read, and whether any arithmetic is needed.

¹⁄₁₆" look for 0.0625

⅛" look for 0.1250-ish (0.1245 to 0.1255&quot

³⁄₁₆" look for 0.1875-ish

¼" look for 0.2500-ish

Although they look simple micrometers aren't easy to use properly. Takes practice to read an ordinary thou micrometer and yours is ten times more sensitive. It's likely that readings will be all over the place at first. The clutch helps, but getting consistent results really requires the operator to develop a sensitive feel by practising on accurate standards such as gauge blocks. Some people get a feel really quickly, a few never get it, and most need several hours practice. Not good to learn on a wonky micrometer.

A thou micrometer will usually detect size errors in jobbing drill shafts because the steel rods used to make them aren't super-accurate. A tenths micrometer should see variations up, down, and around a drill shank, and might detect temperature changes too. If you measure a ³⁄₁₆" drill and get exactly 0.1875", there's a good chance the operator is torquing the micrometer to get the 'right' answer – observer bias. Unfortunately, in the tenths zone it's hard to tell the difference between correct measurements and errors caused by poor technique and faulty instruments.

Measure a few things and tell us what you get. We should be able to work out what the vernier is doing from a few examples.

Dave

Nice demonstration, Bill

… it reminded me of this, from one of my favourite books :

.

MichaelG.

My suggestion of self enlightenment could be easier than relying on machining or emery – just measure and record all digits, then warm the item by a few degrees and record the new digits. Done at the same time with objects multiples in of the smallest item would clearly provide increases of multiples of that smallest increase – if done as a carefully controlled experiment.

A 1” inch by 2” block would likely be sufficient if the operator is able to measure both dimensions without causing a change of conditions. Results could easily be confirmed, as accurate, by comparison with the documented coefficient of expansion for that material.

We (should) all know that machined items should be allowed to completely cool before taking measurements – particularly important for close-tolerance fits.