Micrometer Question

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

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

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

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.

Yes it would be much better to release it by soaking than by disassembly. It looks rather delicate inside and might take specialist knowledge to get it back together and working right.

If all else fails, carburettor cleaner spray is a very aggressive degumming fluid.

Would there be any utility in leaving the micrometer in warm place to assist this to uncongeal (e.g. airing cupboard, 40 degree oven, quick blow dry with the Dyson Supersonic)?

Looking at the drawing further, I would say that those left hand sections of the coarse and fine thimbles with the narrow band of knurling are not in fact locking rings, but are used to calibrate the numbered dials to 0 when the anvil faces are together. So scratch the idea of trying to see if they are a locking ring that can be rotated. All that wil ldo is throw the reading out of calibration! Stick with the microscopists' experience of gummed oil locking their focussing thingies up and continue soaking with degumming fluid/s of choice. The suggestion of heat might help too. A bit of gentle warming can't hurt. Hair dryers work well.

Do not trust patent drawings. They may show the exact product, but since patent specifications are prepared at a very early stage and typically do not change, the drawings will not reflect developments and production engineering. I have written enough to know.

I certainly wouldn't be brave enough to take it apart. If you have access to an ultrasonic cleaner, I'd go for that, with a suitable solvent.

Or lighter fluid usually works quite well, and leaves a very slightly oily residue.

Rob

had it soaked in watch cleaning stuff overnight - no joy

how about isopropyl alcohol, or even petrol ?

It's penetrating oil that it needs. for Plus Gas.

Petrol in preference to IPA, I would think, much better at dissolving goo (usual safety advice applies). Never had much joy with IPA.

But if you can get it, Plus Gas is excellent, or as I mentioned (if you have any) good old lighter fluid.

Rob

Edit - the above assuming it's congealed oil, rather than corrosion that's the issue.

Edited By Grindstone Cowboy on 04/01/2023 16:50:55

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How about PlusGas !!

… if you can’t find any it might help to know that it’s mostly [‘though not entirely] kerosene.

MichaelG.

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Apologies for the late response … I’ve just returned from a 130mile round-trip to the Dentist

Yes … warmth often helps, although the aroma of warm Plus Gas may not please everyone.

What I have found useful on jobs like this is to avoid the temptation to dunk the lot in a bath of solvent, but rather to clean any joint lines with a toothpick, prior to applying the solvent in small quantity, locally.

Not only is it more economical, but the capillary action seems to work more efficiently.

MichaelG.

For what it’s worth …

I am pretty sure this is the second Hagstrom patent relating to the Starrett 221

**LINK**

https://worldwide.espacenet.com/patent/search?q=pn%3DUS2741847A

i.e. the improvement that Starrett asked him to make

MichaelG.

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Edit: and just to emphasise the excellent point made by  john halfpenny:

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Edited By Michael Gilligan on 04/01/2023 20:19:18

I have never found alcohol, meths, rubbing alc. etc very good at dissolving anything other than the plastic lenses on instruments.

Petrol might be worth a try. It certainly dissolves much muck. And was recommended by Mitutoyo to be used to free up sticky plungers on dial indicators on an old service sheet I have. Maybe back in leaded petrol days it had a lubricating effect too? Their recommendation was just a few drops on the plunger. Cleaning the joint edges with a toothpick as MG suggests might help it get into the joint too.

That motion amplifying lever mechanism certainly is a fascinating one. I still can't quite get my head around how it works exactly, even after reading the description on the latest patent MG linked to. Sounds like setting it up could be very fiddly for uninitiated so best to continue with the soaking. It does look as though if you remove that screw that holds the spring loaded knob on the very end of the thimble, you could dribble a little Plus Gas or Petrol or whatever down the tiny hole the end of the spring fits into and goes all the way through, and perhaps help the cause.

Edited By Hopper on 05/01/2023 00:20:48

it had about 5 hours immersed in petrol to no avail. It is now wallowing in diesel and will be there for a few days as I am not about the morrow

If it doesnt free up after its latest bath, try repeated warming/cooling cycles with a hot air gun, I have a lovely little Ambrose Shardlow of Sheffield ( them as forged merlin crankshafts!) 0-1/2" micrometer which was in its original box, spotlessly clean and totally seized, with repeated warming and cooling it freed off, and the cause was congealed lubricant, not a sign of corrosion. Polymerised oils make very good adhesives, but heating will free them! Good luck with it, I wish I had one, just to make ppl jealous you understand!

Phil