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Old 2nd Aug 2021, 12:01 pm   #1
Lloyd 1985
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Default Coughtrie light, stuck glass!

Iíve just recently got my mits on 2 more Coughtrie corner lights, an SW10, and an SG6. For once the SW10 didnít put up a fight and the screws for the glass securing ring came out in perfect order, but the SG6 is another story, it has a nice shaped glass that just screws into the aluminium top, but itís stuck fast, my guess is water got in around the seal and it just corroded over the years. Iíd love to be able to use this light, and at the moment there is a smashed bulb rattling around inside it.

So far my efforts have been copious amounts of WD40, and heating it with a hot air gun as hot as I dare, sticking the swan neck in a vice and gripping the glass with rubber gloves and trying to rotate it, and so far itís not budged even a tiny bit! I tried soaking it in vinegar overnight, that did nothing, trying to rock the glass back and forth has also produced no results! So Iím open to ideas, preferably not involving a hammer... Iíd like to get it apart intact, or at least keeping the glass intact, as that bits harder to replace.

I did think of maybe stuffing it in the ultrasonic cleaner with some sand, but the sand would probably just deaden the ultrasonic waves..

Regards
Lloyd
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Old 2nd Aug 2021, 12:15 pm   #2
Nickthedentist
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Default Re: Coughtrie light, stuck glass!

A good soak in warm water?
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Old 2nd Aug 2021, 12:31 pm   #3
Lloyd 1985
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Default Re: Coughtrie light, stuck glass!

Hi Nick,

Forgot to say I’ve tried that one too, along with Fairy liquid, but it still refused to move! It did blow bubbles in the water though, so there must be a tiny gap around the threads!

Regards
Lloyd
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Old 2nd Aug 2021, 12:31 pm   #4
Station X
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Default Re: Coughtrie light, stuck glass!

Oil filter remover (strap wrench) padded out with rubber?
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Old 2nd Aug 2021, 1:21 pm   #5
Lloyd 1985
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Default Re: Coughtrie light, stuck glass!

Hi Graham,

I’ve not got one of those, but I’ve just had a look for one on eBay, so I’ll get one ordered, looks like it’ll be useful for other things too.

Regards
Lloyd
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Old 2nd Aug 2021, 1:43 pm   #6
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Default Re: Coughtrie light, stuck glass!

Quote:
Originally Posted by Station X View Post
Oil filter remover (strap wrench) padded out with rubber?
That's a good thought but I'd take care: the oil filter remover I've got ends up putting quite a lot of pressure on one point on the thing it's trying to unscrew. I think there would be a risk of breaking the glass shade. Perhaps sufficient padding (lots of bicycle inner tubes, perhaps?) would fix that.

Chris
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Old 2nd Aug 2021, 2:01 pm   #7
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Default Re: Coughtrie light, stuck glass!

Hi Lloyd.

What a pain! I think I would try packing Petroleum jelly around the gap between the glass and the gallery, then use the hot air gun to heat it so that it flows into the gaps.

Leave it overnight , then see if it will move. This worked for me on a similar situation before!

Good luck!
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Old 2nd Aug 2021, 3:14 pm   #8
Lloyd 1985
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Default Re: Coughtrie light, stuck glass!

Cheers for the suggestions, I’ll give the petroleum jelly a go tonight, I’ve got a strap wrench on order, it’s the sort that looks like a bit of old clock spring with a screw thread bit to tighten it, and I’ll make sure to pack it with some rubber.

If nothing works my last attempt might be to cut a slot in the aluminium part with a Dremmel, to try and release the tension on it, probably giving it a bit of help with a big screwdriver, at least I’d be able to fill the slot afterwards and paint over it, but it’s a last resort. Hopefully it won’t come to that though.

Regards
Lloyd
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Old 2nd Aug 2021, 5:30 pm   #9
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Default Re: Coughtrie light, stuck glass!

A careful application of sodium hydroxide drain cleaner into the screw thread will start to dissolve the aluminium surface that’s proving obstinate. Eventually it’s got to let go.

But obviously be sure to rinse it thoroughly afterwards.

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Old 2nd Aug 2021, 6:10 pm   #10
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Default Re: Coughtrie light, stuck glass!

Vinegar or Lemon juice will attack the Aluminium oxide, but not attack the Aluminium, in theory......

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Old 2nd Aug 2021, 6:28 pm   #11
emeritus
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Default Re: Coughtrie light, stuck glass!

Petrol lighter fluid or Plus-gas if you can find some, is far more penetrating than ordinary WD40, although I understand that a proper penetrating oil is available under the same or a similar brand name. I have used ordinary 4 star in an emergency, but the lighter fluid does not have the noxious additives you get with motor spirit. Don't expect to be able to unscrew immediately - steel is not infinitely rigid and you will have a better chance of success by firmly attempting to rotate the screw to and fro to initially loosen the thread nearest the surface while the deeper portion remains fixed. To and fro movement should start to pump out the corrosion and allow the penetrating fluid to progressively penetrate deeper. Patience will probably be required.

Last edited by emeritus; 2nd Aug 2021 at 6:31 pm. Reason: typos
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Old 2nd Aug 2021, 7:51 pm   #12
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Default Re: Coughtrie light, stuck glass!

I was going to suggest putting the whole thing in a bucket of paraffin or diesel for a fortnight, but the caustic soda scheme sounds more likely to succeed.
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Old 3rd Aug 2021, 7:43 am   #13
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Default Re: Coughtrie light, stuck glass!

A lot of times, where I have had difficulty like this, the glass is in fact sticking to a rubber seal rather than the thread.
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Old 7th Aug 2021, 1:39 pm   #14
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Default Re: Coughtrie light, stuck glass!

How are things progressing? Any joy getting the glass shade off yet? Preferably in one piece...!

Hope it's going alright
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Old 7th Aug 2021, 5:15 pm   #15
Lloyd 1985
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Default Re: Coughtrie light, stuck glass!

Hi Peter,

No progress so far, the new strap wrench arrived, I tried it, and it’s still refusing to budge! WD40 seems to have done nothing, so it’s on to the petroleum jelly next! I drew a line on it at the start to see if it moves at all, and so far it hasn’t moved at all... I did remove the rubber seal before I started on it, as I’d also hoped it was just that holding it, it was a bit gooey in the middle, but it wasn’t holding anything in place.

I did have some luck with the SW10 that came with this one, I managed to loosen the corner bracket and remove it from the swan neck part, the threads are kind of trashed, but it does still screw in and out, I was hoping to use the corner bracket from the SG6, as the one in the SW10 is missing a bit, but annoyingly despite having the same part number on both brackets, they both have different threads! At least it gives me more incentive to get the SG6’s glass off...

My brother came up with a good solution of the glass won’t come off, he suggested stuffing fibre optic cable up the swan neck and having the light source elsewhere!

Regards
Lloyd
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Old 7th Aug 2021, 6:36 pm   #16
Jon_G4MDC
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Default Re: Coughtrie light, stuck glass!

Is the problem a painted aluminium body that has a paint layer which has failed.
It has corroded underneath and and swollen up as a result? Then you want something that will attack and dissolve aluminium oxide but so much aluminium base metal.

Any chemists out there? I'm sort of thinking electrolysis.The blokes who restore paraffin stoves and pressure lamps have some ideas on this.
They do scary things with old PC power supplies.

Me? I'd rather there was a good old transformer in the way.
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Old 7th Aug 2021, 7:58 pm   #17
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Default Re: Coughtrie light, stuck glass!

Are you sure it’s not the gasket causing the problem not a easy job as I think the gasket is in a bit of a lip but I would think if you could cut the gasket away that would solve the problem Or at least let any fluid get the the thread Andy
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Old 31st Aug 2021, 1:26 pm   #18
Lancs Lad
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Default Re: Coughtrie light, stuck glass!

How have you been getting on with it?

I'm just being nosey, really, because I love Coughtrie lamps!

Hope you don't mind me asking.
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Old 31st Aug 2021, 5:19 pm   #19
Lloyd 1985
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Default Re: Coughtrie light, stuck glass!

It’s still stuck!! I’ve got the strap wrench on it, and keep giving it a bit of a battering every so often to see if it moves, but so far it’s not moved even a tiny bit. It’s currently got petroleum jelly soaking into it, it has already had WD40 thrown at it (and sprayed into it!) as well as previously trying a soak in vinegar. If this doesn’t work I think I may have to get more destructive with it! At least the SW10 came apart daily easily, so that one will get a respray soon.

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Lloyd
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Old 31st Aug 2021, 7:45 pm   #20
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Default Re: Coughtrie light, stuck glass!

Just another idea. If I remember some physics correctly: Metal has got a bigger shrinking coefficient when cold applied than glass.

That means, if you put the whole thing in the deep freezer, say at -20įC, I would expect the metal shrink more than the glass will. This should result in a more loose fit than now. Right?

But, please keep in mind: This will have a chance only if the glass comes over the metal.

Otherwise (glass thread goes in the metal) I should recommend warming up the whole unit. Again: Metal will expand more than glass, so the glass should come free.

Anyway, applying cold or heat should be done pretty slowly, just to avoid building up too much tension within the glass.

Regards, Joe
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