Ian, Yes I agree with Jason except that as far as traditional mics go I don't think there is much to choose between them and probably the M & W are also made in the far east now ??

As far as the type of micrometre, personally I don't like the digital ones [don't posses one] I think they are bulky and to me as least aesthetically ugly, give me a conventional one any time.

The other point is no batteries to go flat or corrode and always guaranteed to work. My first mic, a M & W bought 1960 at £5 [2 weeks apprentice wages] is still going strong and still accurate.

Just my 5 bits John

If its in good order there is absolutely no doubt the M&W is a far better device. Designed from first principles as a digital micrometer using a linear glass scale with moire fringe sensing its basically a hand held version of the high quality Hiedenhain probes used for precision scientific work, CMM and similar accurate measurment devices. Non rotating, spring driven, measuring rod with speed damping for constant contact pressure it really does tick all the boxes.

Specification is ± 0.002 mm, better ± 0.1 thou, accuracy and they mean it. It really does deliver that accuracy on the bench given the basic care in handling essential when working to such fine limits. Generally instruments with such capabilities are either lab only or have a heavily hedged specification applying in certain circumstances if you do it right and probably mutter the corect incatation. Demoable in the lab but a different matter out in the real world where parts made in my shop need to match parts made in yours. For example the common mechanical micrometer with tenths reading vernier makes a pretty fair fist of indicating a few tenths variation as the acceptable error over any given thou is sufficiently small that the vernier is adequately accurate. But which tenths you are talking about is acompletely different matter because you have no idea where in the overall permitted error band the particular thou you are trying to split into tenths lies so any idea of true measurement is a fantasy. Unless you calibrate the specific thou(s) of interest with gauge blocks first.

All completely academic to the average model engineer but it would still be alovely thing to own. This thread on another forum may be of interest:-

http://www.vintage-radio.net/forum/showthread.php?t=91570

Clive

Edited By Clive Foster on 18/05/2013 23:15:59

Interested in John's comment – how do we know how accurate any measuring instrument is unless we have access to a standards room at the correct temperature. I guess most of us make sure that when the jaws are closed, the instrument reads zero. If the jaws can't be closed, then a standard piece (perhaps slip gauge etc) will be used, but how many of us test the accuracy along the measuring length ?

Personally, I like vernier calipers marked in both imperial and metric, although my 'fractional' vernier reading to 1/128ths" is a brain teaser. My cheapo digital caliper eats batteries, one every 6 months. My caliper with a geared dial is very readable, but only imperial.

It just depends upon the job in hand. Turning a metric piece on imperial equipment. It helps to have a dual scale or readout at the same time – a vernier (like a slide rule) lets you see what is comming up.

My Dad used to say when working out the stress in a bolt. If you use a slide rule, you could see the stress for a range of sizes by looking at the graduations. By comparison, using a calculator, you had to work it out for each bolt diameter.

Bob

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Great story, Phil … Well done !

I would love to know more about that Mechanical digital mic.

… I see the magic word PATENT on the disc, but not a number.

… Do you have any information ?

MichaelG.

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Edit:   I just found this link

Edited By Michael Gilligan on 19/05/2013 08:49:39

my digital mic came from CTC Hong Kong a couple of years ago and cost £26.00 inc. reg. air freight works fine, why pay more?

hi. Phil.

I think every one will be looking out for one from now on!

Looking at that mechanical/ digital mike, I wonder if any manufacturer has thought of adding this functionality to an electronic digital mike / caliper. Ie: readout in MM,inch, fraction,swg,etc etc. I guess the electronic wizzards on this forum could interface a std digital caliper to a 'buzz box' that could do just that.

There is the gauntlet, Anyone going to take up the challenge ??

Bob

Hi Neil,
The output port on my digital micrometer (Unknown make.) outputs data in the 2 x 24 bit format. It works with one of the first display units I built using a PIC micro and an LCD display. The only difference to the calipers is that the decimal point is one position out. It would be easy to change the code to move the decimal place.

Les.

What would be the point?

Ian P

So Ian, I guess there aren't any model loco drawings dimensioned in fractions, using the terms 'full' and 'bare' to indicate the fit required.

Bob

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Phil,

Interestingly: His second picture, [endof the thimble] clearly shows a Patent Date, but …

I just looked on Espacenet, and was surprised to find that's the date of Starrett's patent for the Thimble.

No reference to the worm driven indicator

MichaelG.