|colin hamilton||21/11/2021 09:51:35|
|102 forum posts|
I'm just back from my local car boot where I picked up a cracking little micrometer for only £2. It seems very well made it all lines up on zero and the dials are clear. Only trouble is it's a bit different to anything I've seen before and is marked as 1 to 10000 and I'm struggling to work out how to read it. The left hand side and the number in the window seems easy enough (in the photo 0.18) but what next?
|Andrew Johnston||21/11/2021 10:06:34|
6404 forum posts
I assume the micrometer is imperial and can read to a tenth of a thou. I'd read it as follows. The linear scale on the barrel gives tenths of an inch.The digit in the rectangular window gives hundreths of an inch. Assuming that the scale immediately to the right of the window doesn't move the two scales on thimble together look like a vernier and will give thousandths and ten thousandths of an inch.
|Mike Hurley||21/11/2021 10:15:34|
|247 forum posts|
My thinking also. Andrew beat me to it!
It does say 0 - 1" just above the Steinmeyer label
Edited By Mike Hurley on 21/11/2021 10:17:12
1593 forum posts
I've never seen one in real life as they don't appear very common.
7909 forum posts
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?
|larry phelan 1||21/11/2021 12:23:48|
|1140 forum posts|
Anything being sold in a boot sale at that price has to be suspect !
|Jeff Dayman||21/11/2021 12:35:58|
|2200 forum posts|
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.
|Chris Gunn||21/11/2021 12:39:14|
|414 forum posts|
Bill, thanks for the link to the Peter Marks info on mikes, a fascinating read, where did the morning go?
|Nicholas Farr||21/11/2021 12:52:16|
3137 forum posts
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.
|Brian Morehen||21/11/2021 12:59:17|
187 forum posts
Hi Colin use some twist drils if imperial as mike looks a quick check will give you the right answers looks like a good buy
Good Luck Bee.B
|Andrew Johnston||21/11/2021 13:05:16|
6404 forum posts
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.
|Chris Crew||21/11/2021 20:14:15|
179 forum posts
" 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?"
I wholeheartedly agree with these statements from Dave. It is exactly how I work, although for me it's usually in imperial units. I have read posts that appear indicate to that some contributors work to NPL standards and whilst some people may be capable of achieving this level of precision, or think they are achieving this high standard, I doubt if many actually do in a home workshop. That is not to criticise their work which is probably superb and far above anything I could possibly achieve myself, but it does somewhat call into question the 'holier than thou' attitude as regards accuracy and precision.
I have a 50 year old J&S 540 calibrated to 0.0001" and a 60 year old J&S 1310 calibrated to 0.0002" and whilst I set myself little exercises in working to these theoretical limits, given the wear in the machines, I doubt if anything I turn out is better than 0.001", if that. And in any event I only have 'workshop grade' micrometers and calipers to check the dimensions so I also have to resort to a bit of traditional 'fitting'. My workshop philosophy has always been if it looks right, fits right and works right, then it is right!
|Howard Lewis||21/11/2021 21:28:24|
|5748 forum posts|
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!
|Oily Rag||21/11/2021 22:04:30|
529 forum posts
...How do you go on with fitting a ball bearing? make the housing to the nearest thou (i.e on the loose side ) and then use Loctite? or if it is a little tight 'press' on regardless (pun intended )?
There are ways to achieve engineering fits which are simple if thought through enough. Firstly the tool needs to be sharp and set to centre height (I use an old saw blade and the tangent principle ) and one way to get the infeed accuracy is to set the topslide over to give 1 thou infeed on the topslide to equal 1/10 thou infeed on radius (i.e Sine angle for 1/10 ).This is where a Zeus book is invaluable.
As for your micrometer I am reading it from the photograph as 1 + 8 + 1 + 9 (not being able to see the 9 on the left hand vernier scale I am assuming it lines up! ) = 0.1819"
Again, for accurate measurements I only use a micrometer (a digital caliper is a 'near enuff' instrument ) and I always calibrate the mike against slip gauges set to the size I'm measuring to.
Edited By Oily Rag on 21/11/2021 22:05:13
|Chris Crew||21/11/2021 22:44:40|
179 forum posts
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
|Martin Kyte||22/11/2021 09:53:22|
2636 forum posts
You cannot work to a better accuracy than you can measure. Generally you cannot even do that so you really need a better measurement than the level of prescision to which you want to work. Generally we make things to fit items we already have so measurements are relative/comparitive rather than absolure and provided readings are taken at much the same time temperature can be ignored.
For example take the machiming of a bore to be a close sliding fit on a ground shaft which is sitting on the bench. The first thing I did was to set the lathe up to turn ded parallel over the length of the bore by doing a turning test on a test boobin as normal. By small adustments of the jacking screw at the tailstock end of the Myford I was able to get both ends of the test piece to within 2 tenths over a 3 inch length. Now I cannot turn to as high an accuracy as that but I can measure to it, so I now have a lathe that will at least create a parallel bore. Whilst I was at it I turned the ends of the bobbin to be as close as I could get to the same size as the ground shaft so I had a gauge. Now I have already said I cannot turn to tenths but what I ment was I cannot guarentee the final size but with the two ends of the bobbin I could have 2 attempts. The first end came out around 5tenths under size and a tiny tweek brought the other end to better than 2 tenths. This was mostly luck. Select on test as we say in electronics. Taking a couple of thou off the first end gave me a usable test gauge.
I was now able to bore the casting to receive the ground shaft using the test gauge to check the under size fit. Quick final set of the cut and the final bore was produced which ended up as far as I can tell within half a thou of what I wanted which will do nicely.
If I could only have measure to a resolution of a thou I would have really struggled to get a good bore.
|not done it yet||22/11/2021 11:32:58|
|6518 forum posts|
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?).
|colin hamilton||22/11/2021 12:53:31|
|102 forum posts|
Blimey I can't wait to post my next car boot bargin!! Thanks for the advice. So for the last two digits do I just see which two are aligned and that's the answer?
7909 forum posts
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"
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.
1593 forum posts
Here you go, a little experiment to illustrate the difficulty in trying to measure to too many decimal points, regardless of units.
I picked the ½" block as we know the exact measurement we should be expecting in mm without using a calculator.
Both measurements were consistently repeatable; the anvils and block are still in good enough condition to wring together.
Edited By peak4 on 22/11/2021 16:42:25
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