New Micrometers

[Jon LawesParticipant @jonlawes51698]

I just remember the Boscombe Down Standards lab… if you opened the door for more than a couple of seconds the chap would shout at you…. as a young erk I found it all a bit eye-opening…

[Mike HurleyParticipant @mikehurley60381]

What about an internal micrometer? I know not everyone likes them but personally I do find them handy for most tasks. If requiring a very accurate internal bore I would use a home made go/no go gauge but still use the internal mike when working to ' nearly got there '. ( I'm aware of the issues with them normally only being able to measure the first part of a bore ) . Really don't find calipers work for me as well as micrometers, just a personal thing.

The only drawback I find is having to think backwards when reading the scale and have totally cocked up more than once by misreading it! So, a digital version would be really nice, but they do seem prohibitively priced ( Suppose there's less demand than for external mikes )

Regards

[Dave SParticipant @daves59043]

For bores I use the sliding T gages and then measure those with a mic. Seems to work well in my experience.

I have 'reworked' the gages slightly to make them smoothly operating – This Old Tony has done a video which is basically what I did.

Dave

[Howard LewisParticipant @howardlewis46836]

As said, unless our hobby workshops are accurately temperature and humidity controlled we shall be very lucky to be able to work, repeatably, to 0.0001"

In which case paying lots of money for high grade industrial quality measuring equipment will not be a worthwhile investment.

I got hold of a Swiss industrial (Standards Room ) quality bore gauge, but a couple of anvils and extensions were missing.

Enquired about spares; Spares unavailable, retained for repairs, only.

Cost of a new gauge $5,000 with a 6 month lead time! (i.e. Only made to order )

For my use bought a Die and a tap for the rather small threads (Circa £30 ) and made my own. The accuracy will suffice, since it is, in reality, a comparator between the bore and whatever is used to set the dimension (Slips, Micrometer, Calliper ) So then we are back to the accuracy and resolution of the the standard to which the gauge is compared.

My Vernier Height Gauge was condemned because it had ab error of 0.002" over 18" Since my measurements at one time usually cover a range of a quarter of that, I am prepared live with an error which is probably less than than my capabilities.

Nice to own kit capable of measuring to a micron, but how often is that level of accuracy REALLY needed? is the question.

It would be nice to own a new Rolls Royce. But for a four mile round trip to and from the local supermarket; a waste of money.

Howard

Howard

[not done it yetParticipant @notdoneityet]

We used some very accurate weighing scales at the Radiochemical Centre (this was over 50 years ago). Usual assay balance is to four decimal places of a gram. These, IIRC, were 6 figure ones where we had to leave the item (to be weighed) on the scale pan for 20-30 minutes to equilibrate the temperature of any circulating air within the case before taking a reading – and then go back and check that the weight indication had not changed. The balance room was separate to the main lab.

I remember one fellow tried to weigh a volatile, highly tritiated sample in an unsealed capillary tube. Obviously his weighings kept reducing but he cheated our system of checks. It did not come to light until the next lot of samples, sent for Beta scintillation counting, gave ridiculous results.

The very expensive B-scint. machine had to be completely decontaminated, thousands upon thousands of counting vials were dumped, a lot of analyses repeated and all of us were on urine sample bottles, for health physics checks, for the following week.

[colin hawesParticipant @colinhawes85982]

A decent mechanical micrometer will only develop very small errors due to wear or operational "feel" whereas a digital electronic one could introduce unknown errors so for maximum accuracy I prefer the mechanical micrometer. Colin

[SillyOldDufferModerator @sillyoldduffer]

Posted by colin hawes on 02/12/2021 19:17:50:

A decent mechanical micrometer will only develop very small errors due to wear or operational "feel" whereas a digital electronic one could introduce unknown errors so for maximum accuracy I prefer the mechanical micrometer. Colin

Is that true? What 'unknown errors' are introduced by digital micrometers?

A common type has a digital display mounted on an ordinary analogue instrument with a differential screw.

I wouldn't expect a difference in accuracy. The advantage of the digital display is eliminating misreading errors, and being able to do Imperial/Metric and offsets etc. The disadvantage is needing a battery! The analogue and digital display can be checked against each other. Owners please, do they differ, and if so, which reading is less wrong?

Another type is digital only. There's no analogue scale. Although the example below looks cheap and plasticky to my jaded eye, it's made by iGaging and like the Mitutoyo pictured above reads to half-tenths.

Seems to save space, and I suspect this type doesn't contain a precision differential screw, relying on some other arrangement, perhaps a miniature DRO track and rotation counter. They're not expensive. Does anyone know how they work?

The problem with differential screw micrometers is they depend on the production accuracy of an expensive screw, which is vulnerable to wear, tear and dirt. They're particularly prone to wear on one section of thread if the instrument is repeatedly used to measure similar sized objects. Like the curates egg, worn micrometers are only good in part. A digital instrument could avoid wear problems by not relying on a precision thread, instead directly measuring movement along an optically or magnetically precise track.

Anyone have experience of them?

Dave

Edited By SillyOldDuffer on 03/12/2021 14:45:32

[David JennerParticipant @davidjenner61726]

All bar one of my micrometers, a Dasqua 0-25mm, are second hand Moore and Wright brand, one belonged to my father, so probably getting on for 70 years old (or more?) they all work fine all day every day. I had one digital 0-25 (0-1" purchased from Harbour Freight, this was great to use, verry accurate, but failed after a couple of years. If I was to replace it I'd go for a good brand (read expensive) as the cheap ones seem throaway items or at least a bit of a lottery when it comes to service life. I have one good vernier caliper (Japanese) and two digital calipers,fine for some less demanding jobs and a dial caliper. the digital calipers are great fot estimating cuts, I set the required dimension, set to zere, measure the item and can see the depth of cut required, very handy, but I always check with a conventional mic for the final cut and checks. Works for me!

Concerning my dads mic, still spot on accurate, smooth to operate but the graduations are quite faint now, anyone know of a way to improve these.

Regards

Dave J

Edited By David Jenner on 03/12/2021 15:26:11

[Mike PooleParticipant @mikepoole82104]

EBay has come up with many micrometers that are in near new condition, I have acquired a small collection of mechanical and digital but the most used are the 0.001” and the 0.01mm mechanical. The vernier versions of both give the next level of resolution a definite value but I don’t think I would be far out just guesstimating the tenths of a thou or the hundredths of a millimetre. Digital instruments can lull you to believe what you read on the display but every measuring tool has a tolerance so do not confuse resolution and accuracy.

Mike

[Howard LewisParticipant @howardlewis46836]

For my Reversible Roller Box, i was given a micrometer barrel with a mechanical digital read out.

It had been rejected for having a "One per rev" catch point, but appears to be accurate. It will see very little use, so will last far beyond me!

Howard

[VicParticipant @vic]

I always wanted one of the Mitutoyo mechanical digital micrometers but they were expensive at the time. My standard one works well enough though.

[lfoggyParticipant @lfoggy]

My favoured micrometer is the Mitutoyo QuantuMike. These are of the highest quality and are a joy to use. One unusual feature is the 2mm pitch spindle which makes moving from one end of the measuring range to the other very quick.

[old martParticipant @oldmart]

I sold my Mitutoyo digitals, 0-1, 1-2, 2-3 for about £65 each on ebay, they were in mint condition, so three people got some good kit. I hardly ever used them since retiring, so I turned them into cash and still have mechanical ones in imperial and metric. Ebay can turn up excellent buys occasionally, my 25-50 metric was NOS and made in East Germany, marked DDR and superb quality for £14 including delivery.

 As Mike Poole mentions, the tenths and micron vernier scale micrometers are not really needed as you can easily estimate the finer decimal place without the vernier, I never bother to turn the mic around to read it, even though my mechanicals have the scale.

 One advantage of a digital micrometer is the much reduced chance of misreading it.

Edited By old mart on 04/12/2021 19:31:21

Edited By old mart on 04/12/2021 19:32:53

[not done it yetParticipant @notdoneityet]

Owners please, do they differ, and if so, which reading is less wrong?

I‘ve never bothered to even look and don't intend to.. A bit like having a dog and barking yourself? A check with a gauge block or the supplied standard is sufficient for me. I don’t need that last significant (or insignificant) figure.

It’s a bit like my cheap DROs that only read to the nearest 0.01mm – they read to that, but the spec is wider than that last digit. Still close enough for virtually all operations – where the final measurement (if important) is checked by a micrometer, anyway (after the item has equilibrated with the surroundings).

About the only time when absolute dimensions are required is for replacement parts, held as spares – and there will always be a specification tolerance involved.

[jimmy bParticipant @jimmyb]

This is my reminder not to but cheap rubbish. Repeating error, hence scrap. My digital Mitutoyo has never given any trouble! If money was no object, I'd like one of these, just because…micron mic

Jim

Edited By jimmy b on 04/12/2021 20:42:39

[Mike PooleParticipant @mikepoole82104]

Posted by jimmy b on 04/12/2021 20:42:02:

This is my reminder not to but cheap rubbish. Repeating error, hence scrap. My digital Mitutoyo has never given any trouble! If money was no object, I'd like one of these, just because…micron mic

Jim

Edited By jimmy b on 04/12/2021 20:42:39

That would be just the job for measuring a gnats c*** and fly s*** .

Mike

[colin hawesParticipant @colinhawes85982]

Posted by SillyOldDuffer on 03/12/2021 14:44:17:

Posted by colin hawes on 02/12/2021 19:17:50:

A decent mechanical micrometer will only develop very small errors due to wear or operational "feel" whereas a digital electronic one could introduce unknown errors so for maximum accuracy I prefer the mechanical micrometer. Colin

Is that true? What 'unknown errors' are introduced by digital micrometers?

A common type has a digital display mounted on an ordinary analogue instrument with a differential screw.

I wouldn't expect a difference in accuracy. The advantage of the digital display is eliminating misreading errors, and being able to do Imperial/Metric and offsets etc. The disadvantage is needing a battery! The analogue and digital display can be checked against each other. Owners please, do they differ, and if so, which reading is less wrong?

Another type is digital only. There's no analogue scale. Although the example below looks cheap and plasticky to my jaded eye, it's made by iGaging and like the Mitutoyo pictured above reads to half-tenths.

Seems to save space, and I suspect this type doesn't contain a precision differential screw, relying on some other arrangement, perhaps a miniature DRO track and rotation counter. They're not expensive. Does anyone know how they work?

The problem with differential screw micrometers is they depend on the production accuracy of an expensive screw, which is vulnerable to wear, tear and dirt. They're particularly prone to wear on one section of thread if the instrument is repeatedly used to measure similar sized objects. Like the curates egg, worn micrometers are only good in part. A digital instrument could avoid wear problems by not relying on a precision thread, instead directly measuring movement along an optically or magnetically precise track.

Anyone have experience of them?

Dave

Edited By SillyOldDuffer on 03/12/2021 14:45:32

Reading inaccuracy caused by a reading circuit problem giving a believable false reading. A mechanical instrument can't present such a reading. Colin

[SillyOldDufferModerator @sillyoldduffer]

Posted by colin hawes on 05/12/2021 11:43:53:

Posted by SillyOldDuffer on 03/12/2021 14:44:17:

Posted by colin hawes on 02/12/2021 19:17:50:

A decent mechanical micrometer will only develop very small errors due to wear or operational "feel" whereas a digital electronic one could introduce unknown errors so for maximum accuracy I prefer the mechanical micrometer. Colin

Is that true? What 'unknown errors' are introduced by digital micrometers?

…

Reading inaccuracy caused by a reading circuit problem giving a believable false reading. A mechanical instrument can't present such a reading. Colin

Surely mechanical instruments give believable false readings whenever the screw is worn, anvils damaged, the clutch is iffy, or the frame is bent. My main objection to second-hand micrometers that they are all believable!

I twitch when chaps describe their latest bargains as having 'reputable brand-names' or being 'top-quality', 'high-grade', 'decent', 'good', 'spot-on', 'very accurate' or 'as new'. These subjective terms are inappropriate to an instrument used to take accurate precise measurements. They imply the owner is an optimist rather than an engineer, and certainly isn't a metrologist!

Micrometers have a specification proved by checking them periodically against a reliable standard gauge and recording the results on a calibration certificate. The standard isn't a pre-loved set of Jo-blocks, even if they do look tip-top. Proof and evidence please, not unverified opinion.

I argue digital displays are less likely to mislead when they go wrong because the malfunction is usually obvious: blanks, zeros, eights, negatives and jumping digits etc. In comparison, an analogue display always looks good, even when the instrument is out of tolerance.

Dave

[colin hawesParticipant @colinhawes85982]

If you rely on using the clutch to take readings it is easy to inadvertently include a speck of swarf as it is not felt ; it is my opinion that finger touch on the thimble is more likely to show up such an event . Although I confess I've never experienced it on a micrometer, I have seen a clock digital display with a number giving a wrong figure due ,presumably, to the connecting matrix becoming faulty and losing a part of the digit. Colin

[Brian GParticipant @briang]

My fear with a digital micrometer is the same as with a digital calliper, accidentally coming out of "Abs" mode and not noticing. To try and avoid this I set the "Inc" zero well away from the zero point which hopefully would make this error obvious.

Brian G

[SillyOldDufferModerator @sillyoldduffer]

This graph puts an interesting perspective on accuracy and the cost of achieving it with various machine tools.

The graph dates from 1991 and doesn't reflect improvements made at the high-accuracy end: it's not unusual for a CNC Machine Centre to do rather better than 0.025mm.  Broadly right though.

The cost of accuracy increases linearly up to a 'knee', beyond which the cost multiplies. The graph shows the maximum repeatable accuracy rather than the very best that can be achieved by a skilled operator taking his time and accepting a lot of rejects!

The graph divides in the middle at 0.025mm, which is a thou. 0.025mm sets a boundary between low and high accuracy, and it's about the best that can be expected of Shaping, Planing, Horizontal Boring, Milling machines and Capstan/Turret lathes.

Planing and Shaping are expensive and not very accurate. Although they can be pushed to the 0.025 limit, they perform most economically when less than 0.1mm accuracy is needed. Their high cost compared with milling probably explains why these machines have become unusual. My guess is they are too slow.

Milling gets to 0.1mm fairly easily, but pushing up to 0.025/thou triples the price. It's unlikely that a home-workshop mill can achieve better than 0.025mm accuracy. The same limitation applies to Turret and Capstan lathes: they're good for cheap production and can achieve about the same accuracy as a mill.

High-accuracy requires grinding, including honing, lapping, and hand-lapping. Precision grinding is rare in a home workshop, but industry use it on a huge scale.

Lathe performance as shown on the graph is interesting because it straddles the 0.025mm boundary, getting to about 0.02mm/0.0008" before the knee kicks in, with a practical limit of about 0.013mm/0.0005". Lathes are good performers, capable of reasonable accuracy without costing a fortune. Likewise, milling machines are attractive – reasonable accuracy at low cost. Model engineers don't do much precision grinding because the machines and process is relatively expensive.

That 0.025mm boundary is important in the context of micrometers because it pretty much defines the practical accuracy to which we work. It's about a thou, and doing better than ±0.0005" is really hard. I doubt many home workshops are capable of it, whatever micrometer they have.

Most of us use a different technique I think? I 'fit' parts together, using one to gauge the other, without worrying about exact dimensions. For example rather than bore an accurate 20mm hole and turn a 19.97mm shaft to fit it, I bore a hole of about 20mm, and turn the shaft to slide comfortably into it. No need for a micrometer of any sort, let alone one that does tenths! Fitting is too slow and expensive for production work and spares need to be interchangeable but I don't care!

Does anyone really apply the American System of Manufacturing at home?

Dave

Edited By SillyOldDuffer on 05/12/2021 17:47:21

[Neil LickfoldParticipant @neillickfold44316]

What I do like about mechanical micrometers is their are no batteries to leak and fail the tool. In saying that, I recently did buy a digital depth micrometer, for the purpose of using it like a comparator. I don't think it matters all that much , if electronic or mechanical, as long as you can make the parts you want to. Gauge block sets are in the very affordable range now, with many coming with a certificate of accuracy for each block. So with a good set of gauge blocks and repeatable measuring equipment, new cutting tool technologies, now more than ever, allows home users to being able to easily make interchangeable parts.

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