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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 13th Dec 2017, 4:13 pm   #1
SeanMcK
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Default Hand wound Evershed & Vignoles 'megger' hair spring question

In these are the hair springs meant to return the needle to a predetermined 'rest' position?
I am getting the impression that
1) they are not and that they are simply flexible conductors and
2) the needle should, perhaps?, sit at the last reading until 'shaken' etc.
Thanks.
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Old 13th Dec 2017, 4:17 pm   #2
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

They are just conductors. The restoring force is done by the other meter coil, this counteracts the variable nature of the hand cranked voltage. The needle floats about anywhere when not cranked.

A most ingenious design.
 
Old 13th Dec 2017, 6:15 pm   #3
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Ta Merlin. They are a rather peculiar thing when first encountered.
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Old 16th Dec 2017, 6:59 pm   #4
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

I believe in Megger-speak they're known as 'ligaments', and are made from an extremely flexible, narrow and very thin copper-coloured tape, thinner than a conventional hair-spring.

I have a Record bonding tester with a similar movement that has been corroded by battery leakage. The ligaments look impossible to repair.
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Old 17th Dec 2017, 2:44 am   #5
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

This confused me too. A megger is driven both ways by the generator, the final resting place of the needle is determined by the resistance and will remain there when you stop cranking.
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Old 17th Dec 2017, 2:45 am   #6
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Phil, if they are just conductors could you not use a single strand a wire from a multi strand cored cable e.g. from a test lead?
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Old 17th Dec 2017, 1:30 pm   #7
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Possibly, but it would be most difficult. Imagine wire thinner than an Avo hairspring, but without the springiness. A bit like a single strand of tinsel. Normal copper wire in even the thinnest strand would resist the movement of the coil assembly, and probably even work-harden and fracture in use.
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Old 17th Dec 2017, 4:10 pm   #8
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

I don't doubt fitting it would be entertaining but if the meter is dead without working ligaments it might be interesting to try if nothing else.
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Old 17th Dec 2017, 5:06 pm   #9
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

I can't disagree, but the four ligaments are uninsulated and are only kept apart by the fact that they are flat in section, and remain parallel to each other as the moving coil assembly rotates. Ordinary wire wouldn't behave itself like this.

I'd be really interested to read of any successful ligament repairs at movement level on a Megger. I've got two movements here which I'd love to fix, but have thought about it at some length and decided that I don't need the hassle!
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Old 17th Dec 2017, 8:18 pm   #10
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Ahh I hadn't thought about 'lateral' movement and inadvertent contacts, good point
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Old 17th Dec 2017, 10:18 pm   #11
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Well, Sean, you've got me thinking. Perhaps some very fine enamelled copper wire could be used. Maybe a way could be found to 'stick' three or four strands of 38SWG wire together side-by-side to form a stable but flexible flat conductor? I doubt it would be as durable as the original, but if you've got nothing to lose, it could be worth a try. As I said, I have two movements here with damaged ligaments, so I might have a bash at repairing them once the Christmas rush is over!
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Old 18th Dec 2017, 4:11 am   #12
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Knowing your clock expertise Phil, could thin watch hair springs do the job if they were assembled to counteract each other's springiness?
What metal are the ligaments made from? And for that matter, hair springs? I can't think that they are plain brass or copper or even phosphor bronze.
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Old 18th Dec 2017, 9:09 am   #13
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Hi Sam,

That's not a bad idea, actually, although the ligaments all curve the same way so what's needed is to temper the hairspring material to reduce its springiness. Maybe heat treatment? I have a clock repairer friend who can probably give me some suitable scrap springs with which to experiment.

As for the material itself, I've no idea what it is but it looks like copper. It certainly turns the same blue-green colour when it corrodes. "A strand of tinsel" describes its physical properties quite well! It's going to be the devil's own job to solder it.
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Old 18th Dec 2017, 3:09 pm   #14
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

What about the hair springs from a dead moving coil movement?
Re a made up 'side by side' wire, would a platted 'strand' tend to be flatish?
That said I have just severely shaken a single strand of very fine copper wire and there is relatively little movement. Given that the lengths involved are probably quite short and that the ligaments would be supported at both ends I wonder if the 'wander' would be enough to bring adjacent ligaments into to contact with one another and if they were enamelled.......

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Old 18th Dec 2017, 4:54 pm   #15
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Surely a bit of Christmas tinsel would do fine. A problem to solder, but I think it could be secured with a blob of solder each end. Try to lead it vertically away from the axis of the coil bearings. I have seen variations of that on a commercial unit. wme_bill
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Old 18th Dec 2017, 5:40 pm   #16
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

I doubt whether modern tinsel is conductive, due to Health and Safety considerations Bill! One other thing I wondered about trying (if I could find some) was that super-flexible wire used in vintage headphone leads and old telephone cords, the sort that's twisted together with cotton threads and is a right pain to solder. There's a proper name for it which escapes me at present. It might even be 'tinsel wire'.

Good idea Sean, now you mention it, I do have an open-circuit movement from a Taylor 40kOPV multimeter which should yield plenty of hairspring wire to play with.
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Old 27th Jan 2018, 8:49 am   #17
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Quick update: I am still actively trying to repair one of the ligaments of my Record Bond Tester's movement. It is proving very difficult to clean the end of the ligament and 'tin' it.
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Old 27th Jan 2018, 8:57 am   #18
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Not like you Phil, ace with an iron.
Why? Is it the material that is oxidising? Iron too hot?
Will it clean with LaCo plumbers flux? Its slightly corrosive but will wash off.

If it won't solder, how about a mechanical joint, a split brass nubbins like a watch? Then solder the brass to whatever.

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Old 27th Jan 2018, 11:39 am   #19
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Good idea Sam, I've got some LaCo flux (which I normally use for tinsmithing at one of my places of 'work'!) so I'll retrieve it next week and give it a try.

Perhaps a few pictures, taken through my illuminated magnifier, will give you some idea of the small scale of the ligaments and the problems faced by would-be repairers. I have two of these movements, both with damaged ligaments. The first two pictures show the first movement, with a damaged control coil ligament which is plain wire and finer than a human hair, which you can just make out. The third picture shows the second movement which has a damaged deflection coil ligament, visible above the spindle. This is a flat-section 'tape' as it carries a heavier current to the deflection coil, which has a resistance of just 1 ohm. It's this latter that I can't get to 'tin' but some acid flux may just work. The ligament appears blackened, and I think this is due to acid fumes from the leaking NiFe cell which has damaged much of the internal wiring as well.

As you can hopefully appreciate, just holding these extremely fine wires is difficult in itself as they are smaller than the gaps between the closed jaws of forceps or tweezers...

I sometimes wonder why I take on this vintage micro-miniature stuff

Phil
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Old 27th Jan 2018, 12:00 pm   #20
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Default Re: Hand wound Evershed & Vignoles 'megger' hair spring question

Quote:
I sometimes wonder why I take on this vintage micro-miniature stuff
Because only you can!

What is a Record Bond whatsit anyway?

Sam
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