Inch/metric micrometer

[Asquith]

Not an antique, but unfortunately GKN Shardlow Metrology are history.

This is a dual inch/metric micrometer.

The pitch is 1/50" instead of the normal 1/40" for an imperial mic. This pitch allows the inch axis to be horizontal, while the millimetre scale has to be helical.

Reading it takes some getting used to, but then I never feel at home with a metric mic anyway.

There’s a slight compromise involved in using the mic with either system.

Inch Scale: Horizontal line divisions are 0.020". On the thimble the numbers (0, 2, 4 etc) are thous. The small divisions are 0.0004" which seems odd, but then this helps with the metric scale. This isn’t really a problem, it just seems strange that odd whole numbers of thous don’t have their own line

Metric scale: Easy to read to nearest 0.01 mm. Interpolation is trickier because of the angle of the line, but then it’s not designed to resolve beyond 0.01 mm.

Example of a reading: 0.02". Millimetre (red scale) subdivisions are 0.5 mm (note that metric numbers on thimble are also red, but may not show up here). Hence metric reading here is just under 0.51 mm (actual figure is 0.507).


Another example: Measuring 0.5" slip gauge.

The locking mechanism is unusual. Press the button gently in to lock, press it out (from the other side) to release. Seems very effective.

Here’s an abstract of the 1966 GB patent (Arthur Harold Mills). An alternative arrangement shown in the abstract has two helical scales and just one set of graduations on the thimble.

espacenet - Bibliographic data

The only other micrometer I recall seeing with an inclined scale is one of Rivett’s very old ones:-

http://www.practicalmachinist.com/v...nglish-micrometer-thread-compensation-220163/

 

[pistonskirt]

Oh dear.....back when I had employees there came a point where I removed everything imperial from the workshop & replaced with metric only, including machine specific setting mics & vernier calipers, everything imperial or dual scale went home or was locked away in my personal tool chest.

If I had one of those mics I fear that I would have to hide it from myself

Very interesting to see one nonetheless, thank you Asquith.

regards

Brian

 

[PeteM]

The Ambrose Shardlow company also made the for others to brand; such as Regal Beloit (a maker of cutting tools). The spindle lock on these is also a bit unique.

 

[Asquith]

Pete,

I followed up your lead, and it took me to one of Rivett’s posts on an older micrometer which used a similar principle. However, it was far more interesting because it had, in effect, two thimbles, connected together:-

http://www.practicalmachinist.com/vb/general-archive/ever-see-micrometer-like-72697/

I’ve become very impressed by the quality of Shardlow micrometers, and by the maker’s enthusiasm for trying something different. Here’s an advert for their 'Check Reading' inch mics:-

http://www.gracesguide.co.uk/images/3/34/Im1943MWYB-Ambrose.jpg

I haven’t seen one in the flesh, but there is a row of four numbers alongside each division> These represent one of the four possible numbers of thous which correspond to that thimble division, given that each 100 thou increment on the barrel is split into four 25 thou divisions. This provides a cross check on the user’s reading. I note that the advert dates from 1943, so I wonder if they were catering for the many inexperienced workers drafted in to do war work.

Here’s a Shardlow 1" - 2":-


A handwritten receipt in the box says that it was bought by Mr Thorpe for £2 from Gerald Grimmett in 1962. I have list prices for the mic in 1958 and 1964 being £3 18s 4d and £4 10s 8d respectively.

I don’t know that the sloping lines offer much advantage. The divisions on the thimble are in 0.0005" increments rather than the typical 0.001". This means that the 0.0001" vernier only needs 5 divisions instead of 10. Therefore you don’t have to look half way round the barrel to see where the lines coincide, but I think I prefer the simplicity of conventional divisions.

Very nicely finished, and I like the locking arrangement.

Sorry my test report is half a century late!

 

[PeteM]

Both Rivett's link and the "check reading" micrometer are ones I've never seen examples of. Thanks for posting them.

Personally, I think the slant-line micrometers are a decent innovation, especially for a large shop with lots of micrometers coming in and out of calibration and a mix with some inexperienced users. Micrometer thimbles and sleeves often slip just enough (or are adjusted that way) that it's hard to know at a glance what .025 one is on (the line is just obscured by the thimble). Once I got used to it, the slant lines seemed just as easy to read as the usual lines. B&S, as far as I know, was the maker that did the most to popularize this.

 

[Asquith]

Good point about line slippage.

No such problems with this:-

This was probably GKN Shardlow’s ultimate micrometer, and I think I might come to regard it as my ultimate. Digital, compact, nice and feely, and it has an excellent vernier, too. The thimble size is quite generous, and only has 20 divisions, so these are quite widely spaced. This means that there’s no difficulty in deciding which pair of lines line up, as seen here:-

 

[PeteM]

Asquith, I'm pretty sure the Shardlow digital micrometer was built for them by Slocomb. Before donating my micrometer collection I had examples (same digital mic) from Slocomb (both old and new versions) and others built and branded for Central Tools and Snap-On. Moore & Wright also sold an example. Note also that the Neill Tools Group now owns both the Shardlow and Moore & Wright brands.

FWIW, Slocomb was bought out and had production (including their digital mic) moved from Providence, RI to Glastonbury, CT around 1953.

Don't know about the mechanism inside these fairly modern mics, but it might be essentially identical to the 1920 Davenport-Slocomb mic. The Davenport patent was 1916, I believe. The round windows and digit spacings are essentially identical in the old and modern versions. In addition, both the 1920 and more modern versions have the same retaining screw in the housing (and the same shape housing); suggesting the internal mechanism is either the same or nearly the same. If so, it's a remarkably long-lived design -- 80 years or so in production.

 

[ed.hopson]

Shardlow for auction on ebay right now-

Have a look at this micrometer, if this your thing-
Ebay item [mis-identified as a M&W] #190624618311
Here's the link-
MOORE & WRIGHT 0-1 IN / 0-25 MM Micrometer made for Regal Beloit South Beloit IL | eBay

Ed Hopson

 

[Limy Sami]

I have, and regularly use several Shardlow mics, which I like and have never had any problems with them, they're cheaper 2nd hand because they haven't the name.

An old guy who used call in for a cuppa, (he'd been an inspector and calibration guy,) told me they were good, and would check my stuff against his ''inspection grade'' blocks for me.

The Shardlows seldom needed tweaking.

FWIW I think the 2" & up Shardlow frames are steel and not iron.

 

[Tyrone Shoelaces]

I've got a " Shardlow " 1"-2" mike, the spindle lock is different to the one in the photo. It's a small round knurled ring on both sides of the frame that you can turn with your fingertips. Less prone to damage than the lever type I suppose. I also think the frame is steel but it's currently at work so I can't check it at the moment. One of my workmates was retiring and he it gave it to me along with several unusual 0"-1" mikes including some by " Slocomb " and " Lufkin ". One of my pals who is an Inspector has one of the digital mikes like the one illustrated but I don't think he ever uses it.
I'm not sure about the Inch/metric mike, it's an accident waiting to happen in most shops.

Regards Tyrone.