Unknown micrometer

Attachment 39375

Not sure that this is the right place to post this, my apologies in advance if I got it wrong.
I have this micrometer which was part of my dad's tools when he died, it must be at least 80 years old and I have no clue what it would be used for.
It was manufactured by Ambrose Shardlow in Sheffield. I have downloaded one of their tool catalogues (company closed many years ago) and can not find it, also done Google searches and spoken to many machinists with no joy.
The company also manufactured aircraft engine parts during WW2.
Hoping that some of our erudite members will know what it is for.

I can offer two guesses...

Used to measure projection of some feature from the curved surface of a structure

or

The radius of curvature can be calculated from the height (sagitta) of an arc above a known chord; see...

https://www.homemadetools.net/forum/...016#post179895

Purely guesses. I've never seen or used one as shown in the photo.

Thanks Marv, I had similar guesses and wondered if it was more of an in-house unit to Ambrose Shardlow for measurement on crankshaft journals.

I have never seen one like that either, but I would second the thought that is was some custom measuring tool used for a some task very specific to the place that your dad worked.

There was an old gent around here that had a small used tool shop as his sort of semi-retirement job. He previously had been an instrument maker that sold and repaired measuring tools. He told me that at one time a pretty significant part of his business was making custom measuring tools for the GE jet engine plant in Lynn Massachusetts when they were in their heyday. He had some pictures of various fixtures and jigs he had made for them, some of them quite complex and interesting. Most of that business went away when CMM's and the like came into play. Great old guy, full of stories. I miss him.

A key-way or recess depth measuring tool for a specific diameter shaft? Looking at the size of knurled knob on the attachment it would appear to have been made interchangeable, rather than a single purpose made tool.
A late thought! A specific boring bar tool setter. I knew I had seen one before! :-)

If you zero the micrometer, where does the anvil sit on the hole? Is the knurled screw (large one) to adjust the height of that adapter piece that is of the working end? How about that small knurled screw, does that allow the reading line to move? I probably am using the wrong nomenclature to describe the parts of a micrometer.

The retired machine shop teacher named Lyle Peterson (Tubalcain on utube) would probably know. Send him a picture. His email address is pete22@mchsi.com

Marv and metric_taper have good justifications, especially what position the spindle tip is from the radius at zero. My question is the tip itself, is it flat (conventional), reduced diameter, or pointed?
Another detail about the clamp-screws; appear to allow zero anywhere. That makes possibility recording difference (instead direct measurement), compared to a standard; or vice-versa of course.
No doubt micrometer head is Shardlow, but foot was generated as specific tooling, in manner described post 4 by clavius. If was commercial, high likelihood to be finished satin chrome as the thimble and body.

Next page post 13 Tonyg reports
"Hi ,
The tip is flat and it does allow it to zero anywhere."

Quite conclusive factor there; it's a comparative instrument, not absolute. Could set any kind of plunger etc, if maintaining linear axis to it.

As a guess I would say it was used to measure the depth of key ways or splines on a given production part as the shaft size would have to constant looking at the base of the mic,depending on the shape of the anvil tip. Interesting

I recon your right on the money as a boring bar depth setting tool,the only trouble is you would have to read it from the back of the bar due to the constant radius

The thumbscrew on the shoe allows you to set the depth anywhere along the rod that goes into it so you can zero it at any point. The large knurled screw is for course adjustment and the small one is a ratchet/light torque slip type adjuster so that when the tip touches it then turns without advancing anymore.

I have sent the pic through to Lyle. I will post his reply when I receive it.

Quote:

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Originally Posted by Toolmaker51

Marv and metric_taper have good justifications, especially what position the spindle tip is from the radius at zero. My question is the tip itself, is it flat (conventional), reduced diameter, or pointed?
Another detail about the clamp-screws; appear to allow zero anywhere. That makes possibility recording difference (instead direct measurement), compared to a standard; or vice-versa of course.
No doubt micrometer head is Shardlow, but foot was generated as specific tooling, in manner described post 4 by clavius. If was commercial, high likelihood to be finished satin chrome as the thimble and body.

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Hi ,
The tip is flat and it does allow it to zero anywhere.

Hi all,

Firstly, thank you all for your contributions - all of which are probably right. It has given me some extra ideas on what I might be able to use it for, although it may also just sit in the display cabinet in the workshop as a conversation piece.
Secondly, I have received a reply from Lyle which I will paste below:

'Hi Tony. This is my best guess. All micrometer companies made what they called micrometer heads. These heads were sold to shops who needed special micrometers. They would then manufacture or machine an attachment that would fasten onto the micrometer head. Always for special purposes or for inspection, etc. you will probably never know exactly how this micrometer was used or what its purpose was. There would’ve been tens of thousands of variations throughout the world'

Kind regards to you all,

Tony.

Quote:

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Originally Posted by Tonyg

Hi all,

Firstly, thank you all for your contributions - all of which are probably right. It has given me some extra ideas on what I might be able to use it for, although it may also just sit in the display cabinet in the workshop as a conversation piece.
Secondly, I have received a reply from Lyle which I will paste below:

'Hi Tony. This is my best guess. All micrometer companies made what they called micrometer heads. These heads were sold to shops who needed special micrometers. They would then manufacture or machine an attachment that would fasten onto the micrometer head. Always for special purposes or for inspection, etc. you will probably never know exactly how this micrometer was used or what its purpose was. There would’ve been tens of thousands of variations throughout the world'

Kind regards to you all,

Tony.

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Indeed this is very true. Those micrometer heads are still available of course, all of the companies that make such tools offer then in many styles:

https://www.google.com/search?client...icrometer+head

Still very cool to have something like that from your dad. Such things are small treasures. I have any number of old tools that I ended up with from friends and relatives that are no longer with us. I think of them every time I use them, even if that use is infrequent. I read someplace that using a tool that was made for you or given to you by someone is to "shake their hand in friendship." I like that and find it to be so in a way.

Quote:

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Originally Posted by clavius

.......snipped........I read someplace that using a tool that was made for you or given to you by someone is to "shake their hand in friendship." I like that and find it to be so in a way.

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Many relate to that. Family or friended tools, not surprising to sense a reaction to personal items, especially tools. Just reading his [clavius] post, I recall such occasions, though rarer, in property belonging to those you've no other connection at all.
Might be from era a person identifies with; though a boomer, somehow circa WWII tools and machines 'find' me.