micrometer restoration

HI all,

When I bought my lathe (second-hand - its a 3 3/4" Corbetts branded lathe from the 50s or 60s), it came with some tooling and a complete (contemporary) set of micrometers from 0-1" to 3"-4".

Up until yesterday evening I've only had cause to use the 0-1" mic., however on trying to use the 0-2" mic., I found that it was completely seized. The spindle is wound fully forward, touching the anvil and neither the thimble nor the ratchet will turn - I haven't tried to force it.

Is this something I would be able to service myself? it is likely that soaking it for a few days in something (some form of solvent...white spirit?) will free it up? Or is it something best left to a professional?

Thanks fro any advice. It would be great to get this tool back up & running, earning its keep

cheers

Paul

Paul,

I see no reason why you can't overhaul the micrometers ... It's a very simple mechanism [albeit well-made] and you have a good one available, as an example.

I would try PlusGas formlua A dismantling fluid [readily available], but I wouldn't bother using a bath of it ... Capilliary action usually works fine.

MichaelG.

Thanks Michael.

It seems that Maplin's do a can of PlusGas formlua A - I'll try and can pick one up at lunchtime & see what happens this evening.

Cheers

Paul

Paul Davies 8:

I suppose that mic can only have seized through rust or oxidisation, etc of the oil on the screw. Rust would be bad news, of course. The next question once the mechanism is free is what lubricant to use to protect the mechanism in future?

I have never heard of a mic seizing before. Are you sure the clamp isn't on?

Good point. That is indeed possible...though it is also possible that the clamp is stuck, too. (BTW, its an M&W model 940)

cheers

Paul

Paul Davies 8:

My M&W cat lists the 940MX with locknut, rather than clamp, and alternative anvil to give greater range. Is this your type?

As far as I can see, this one on ebay is the same as mine.

cheers

Paul

Any kind of non-gumming oil. Gun oil, clock oil, hydraulic oil or even synthetic engine oil

Take the clamp nut off to ensure the penetrating oil gets in there. It is very simple to dismantle, remember it is only an accurate nut and bolt. I give my micrometers a puff of WD40 + PTFE type spray about once a year, even the little used ones remain free.

Thanks all for your posts

I think I'll be able to resurrect this mic. this evening, with a little more confidence.

Cheers

Paul.

Paul Davies:

Yes, that looks like the catalogue item:

Edited By ega on 13/11/2015 15:16:42

Well,

Having got home and done a little more digging, I can confirm that the mic. is indeed a model 940, from the engraving on it and that the problem is a combination of the clamp wheel being tightly done up as well as the innards being all gummed up.

I've given it a generous dose of penetrating oil and have been able to slacken the clamp off and the thimble now turns freely out to .920", where it stops & is well & truly stuck. The ratchet also refuses to move.

I'll leave it to soak in over night, and see how it is in the morning.

BTW, I unscrewed the clamp completely and discovered, where the vernier section screws into the cast 'C' that there seems to be a lot of rust.

I suspect that despite the clean exterior, this mic may have been for a bath at some time in the past...

I may just bid on the other 940 on ebay...just to ensure I have a fully functional set., in case this one proves too far gone.

cheers

Paul.

Starrett sell a small bottle of oil particularly for this type of application.

Rather than force it. Give it a spray of penetrating oild and just keep working the thimble back and forth. it takes time but will come free eventually. Keep re spraying to wash out any corrosion debris which could be getting trapped in the thread. I've done this method in the past with great sucess. My mic' is 40 years old now and has been neglected before I got back into engineering. (Hobby that is).

A quite good penetrating oil may be made from a 50/50 mix of acetone and ATF (Automotive Transmission Fluid)

Mix it up, shake it up and keep adding to the seized component as the acetone evaporates. It may take a long time, but it doe seem to work quite well.

Vibration will help the effect to keep rapping it, sharply, but not to hard.

Lots on the net about it e.g. HERE

All little progress over the weekend...

With generous application of penetrating oil...time...and a little gentle persuasion, I have been able to get the thimble to fully unscrew from the spindle/thimble assembly. As such, I should now be able to get the full range of measurement out of the mic.

I've given the sleeve a good clean, but since the ratchet is still not working, I've set the thimble/ratchet assembly aside, full of penetrating oil, to give it more time to steep.

cheers

Paul

Try dismantling the ratchet assembly, it should come apart by undoing the screw in the thimble end? & give it a brush with a stiff toothbrush or one of those fibre glass brushes that inst.techs use.. available from Maplins.

George.

Hi George,

I've tried that. The screw in the top is stuck fast. I don't want to force it and risk damaging the screw-driver slot.

That said, I did notice that I'd starting to get a tiny amount of movement in the ratchet, now that it has been treated to a good soaking in penetrating oil. I'm hopeful it will eventually free up, given enough time & oil.

cheers

Paul

Bandersnatch:

"Starrett sell a small bottle of oil particularly for this type of application."

Thanks for the suggestion - now to find a UK supplier.