Micrometer Question

[Justin ThymeParticipant @justinthyme24678]

this little micrometer came into our possession along with some other engineering stuff, it has an unknown history

It seems quite accurate in comparison to other ones that we have. However part "A" does not move separately from art"B" and there is no torque release (normally you can only tighten a micrometer to a certain tightness, as I'm sure you will all know)

Not sure what the screw spring assembly does on the end.

I feel the whole thing is jammed, some release oil has not helped – so before I start to use some real effort to turn "A" with respect to 'B'. Has anyone got any suggestions or knowledge of this micrometer, and how best to proceed – I don't want to make things worse

Edited By Justin Thyme on 03/01/2023 21:04:44

[Justin ThymeParticipant @justinthyme24678]

[Mike PooleParticipant @mikepoole82104]

YouTube 221 this may help

Mike

[DC31kParticipant @dc31k]

The 221 stamped on it is the Starrett model number

Google 'Starrett 221 instructions' and follow some of the links.

You will find:

https://3dwarehouse.sketchup.com/model/ue7fb53b1-e9e8-4935-977a-5c87a7156b2d/Starrett-221-micrometer?hl=en

which leads to:

https://worldwide.espacenet.com/patent/search/family/023454424/publication/US2267332A?q=pn%3DUS2267332A

and there is a Hollywood movie of it as well:

[Michael GilliganParticipant @michaelgilligan61133]

Aside from being a Starrett … which is a good start … it’s a 221 … which is even better.

Treat it gently: You may get some ideas from this

.

.

MichaelG.

[Grindstone CowboyParticipant @grindstonecowboy]

That's clever!

Rob

[Michael GilliganParticipant @michaelgilligan61133]

Looks like we all gravitated to the same place !!

It must be Lust …

 

MichaelG.

Edited By Michael Gilligan on 03/01/2023 21:52:47

[Phil PParticipant @philp]

I want one…………..I certainly dont need one, but I want one

[peak4Participant @peak4]

At $799, I thought about it for a moment, but fortunately they seem to be discontinued.
https://www.starrett.com/metrology/product-detail/T221XL

Bill

[egaParticipant @ega]

[SteviegtrParticipant @steviegtr]

When i saw this thread I thought i had one. But it is different & not Starrett. It is a Moore & wright ModelDR961.

I think it works the same though. Anyone know.

Steve.

[KWILParticipant @kwil]

Steve,

I think you would find it is a geared system. I have the metric version.

K

[Justin ThymeParticipant @justinthyme24678]

thanks for the replies but they don't really address my problem. Part 'A' in my picture (Coarse Thimble Assembly) does not move in relation to Part 'B' ( Fine Thimble Assembly)

This is potentially a nice little tool and I don't want to start trying to force anything with vices, pliers and hammers. Not even sure if I should be trying to get a bit of thin oil between the stuck bit.

[SteviegtrParticipant @steviegtr]

Posted by Justin Thyme on 03/01/2023 23:25:56:

thanks for the replies but they don't really address my problem. Part 'A' in my picture (Coarse Thimble Assembly) does not move in relation to Part 'B' ( Fine Thimble Assembly)

This is potentially a nice little tool and I don't want to start trying to force anything with vices, pliers and hammers. Not even sure if I should be trying to get a bit of thin oil between the stuck bit.

I know this is clutching at straws but is the anvil locked on the knurled screw on the u part . Sorry if a stupid Q&A

[HopperParticipant @hopper]

Whatever you do don't use force of any kind! Too lovely of an instrument to be ruined by that.

First thing I would focus on would be that locking ring mechanism. There is usually a tapered sleeve or similar in there than that can jam up if left in the locked position for eons. I would try WD40 in there and work it gently back and forth. Everyone has their favourite releasing fluid, but I find WD40 contains a good solvent that gets rid of most gummed up oil etc, and it lubricates as well, which some releasing fluids don't.

Otherwise I would stand it upright and try drizzling a bit of WD40 etc down the sleeve for a few days, and see if that helps. If not, complete submersion in something similar might be in order. If that does not work, find someone with an ultrasound tank and put it in there for a bit. Gunsmiths and instrument shops often have such tanks.

Maybe try emailing Starrett in the USA? Or try one of the websites for forums for Starrett collectors.

Edited By Hopper on 03/01/2023 23:46:39

Edited By Hopper on 03/01/2023 23:48:24

[SteviegtrParticipant @steviegtr]

Posted by Hopper on 03/01/2023 23:43:21:

Whatever you do don't use force of any kind! Too lovely of an instrument to be ruined by that.

First thing I would focus on would be that locking ring mechanism. There is usually a tapered sleeve or similar in there than that can jam up if left in the locked position for eons. I would try WD40 in there and work it gently back and forth. Everyone has their favourite releasing fluid, but I find WD40 contains a good solvent that gets rid of most gummed up oil etc, and it lubricates as well, which some releasing fluids don't.

Otherwise I would stand it upright and try drizzling a bit of WD40 etc down the sleeve for a few days, and see if that helps. If not, complete submersion in something similar might be in order. If that does not work, find someone with an ultrasound tank and put it in there for a bit. Gunsmiths and instrument shops often have such tanks.

Maybe try emailing Starrett in the USA? Or try one of the websites for forums for Starrett collectors.

Edited By Hopper on 03/01/2023 23:46:39

Edited By Hopper on 03/01/2023 23:48:24

Here Here. good idea Hopper. Plus gas is superb at releasing stuck parts. Readily available in the UK.

Steve

[HopperParticipant @hopper]

And if all that fails, on most micrometers, if you take that little spring-loading tensioner device off the end,the thimble is mounted on the exposed spindle by a taper. So if you carefully hold the thimble and tap the end of the spindle downwards onto a block of hard wood etc on the bench, the thimble should come loose on the taper and come off.

You can then inspect the thimble and try to work out how to get the two parts apart, or at least have better access for your releasing fluid.

Would be best to read some material/watch some videos on micrometer disassembly in general first so you have a bit of a roadmap.

[Michael GilliganParticipant @michaelgilligan61133]

There were two patents mentioned in the video

MichaelG.

[Justin ThymeParticipant @justinthyme24678]

I have found boiling stuff in oil a good way of freeing stuff up, but may keep that tactic until later. Will dry a few days of wd40 type stuff, I also have a contact at a staretts factory, I may email her.

anyway, may be to clarify where it is not stuck, this is it dismantlement as far as I can

[HopperParticipant @hopper]

Ah, ok, so it's the actual interface between the one thou main thimble and the tenths of a thou secondary thimble. Which would have to be some kind of friction drive so that when you turn the main knurled area on the tenths thimble, it turns the thou thimble, which must be hard mounted to the spindle in some way.

A drawing of how that is done would be muy helpful. Perhaps MG's suggested patent application drawing? No idea on how to look that up. Ask MG.

[Michael GilliganParticipant @michaelgilligan61133]

One of the patents has already been kindly mentioned by DC31k …

but for ease of reference: **LINK**

https://worldwide.espacenet.com/patent/search?q=pn%3DUS2267332A

The other one should be easy enough to find, by searching Espacenet on the claimant’s name

[ presumably either Hagstrom or Starrett ] … it only gets brief mention in the video.

MichaelG.

 

Edited By Michael Gilligan on 04/01/2023 07:31:18

[OldironParticipant @oldiron]

I have a couple of 221's. Gready I know but I do collect Starrett tools. You can still get many of the spare parts from Starrett.

regards

[Robert Atkinson 2Participant @robertatkinson2]

I'd start by giving the thimble assembly a good soak in penetrating fluid. Leave the little end cap off to let it get in.
The torque limit normally provided by a ratchet in a small extension to the timble is built into the larger diameter part of the thimble on the 221

Robert G8RPI

[HopperParticipant @hopper]

Here you go. I have not had time to study it in depth and figure out exactly how it all works.

But the first thing that jumps out at me is that the fine thimble is in two pieces and one has a slot in it like it is meant to clamp down on the barrel it rides on. Is it possible the left hand part of the fine thimble with the narrow band of knurling on it is a locking ring of some sort? Maybe try holding the wide knurled right hand half and see if you can "unscrew" the narrow knurled band left hand half.

Or ditto with the narrow knurled band at the left hand end of the main coarse thimble. IT also is a separate piece.

Note that the main spindle does not go right through but has a sub-spindle that screws into the end of it, and a "motion amplifying lever" whose functioning I have not figured out. But it means you cant release the main spindle by tapping on the end to release if from the taper until all the fine measurement parts have been removed — somehow!

EDIT

And here is a tiny pic of that motion amplifying lever from the Practical Machinist forum. Looks like you must be able to remove the fine thimble to gain access to it. No idea how though!

Edited By Hopper on 04/01/2023 10:41:50

Edited By Hopper on 04/01/2023 11:03:28

[Michael GilliganParticipant @michaelgilligan61133]

Given that [as very clearly stated in the video] Starrett uses the barrel sleeve as a bearing surface for the coarse thimble … I would guess that the problem might simply be congealed lubricant between those two surfaces: it’s been enough to lock-up many a focus-mechanism on microscopes.

As previously recommended : ‘PlusGas Formula A’ usually works wonders.

MichaelG.

[Author]

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