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Old 26th Feb 2020, 3:59 pm   #1
Nickthedentist
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Default Ideas for stabilising a crack in a Diakon GPO 706 telephone

Hello everyone,

I've just bought a red 706 phone, an early one stamped "59" underneath, so the very first year of issue. Its case is made from Diakon, i.e. PMMA or Perspex.

It looks fantastic, with it's super-glossy, slightly translucent, red finish and chrome fingerplate but has a crack on the back, spreading from the cutout where the cords emerge up towards where the handle could be fitted. Being on the back, it's not very visible normally, but I'd hate it to spread to somewhere which shows.

What should I do? Would cleaning out the crack and a bit of Araldite be sensible? Or should I use a solvent (but would that be risky)? Reinforcing mesh of some sort on the inside? I'm reluctant to use the engineers' trick of a small hole to stop the crack propagating, but if I could disguise it, I might consider it.

All ideas welcome.

Nick.
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Old 26th Feb 2020, 4:19 pm   #2
Bazz4CQJ
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

You need to drill a small hole just ahead of the crack, When the crack hits the hole it will stop. I was told about this many years ago and have successfully used this method on a number of items, e,g, aluminium castings, plastic wheelie bins. A hole of 2 or 3mm should be ok.

B
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Old 26th Feb 2020, 4:27 pm   #3
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

It's called 'stop drilling' which is what Nick wanted to avoid. Having said that i would probably do the same.

If there's proper separation of a crack i use araldite provided it's compatible with the material, but if it's one of those cracks that you can't get into you need something less viscous.. Would fibreglass mat adhere if the material was scuffed up? Not sure.

Dave
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Old 26th Feb 2020, 4:30 pm   #4
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

This might sound a little weird, but Sugru might work since it will grip around the crack and hold the back together. However if the plastic actually is translucent it might show.
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Old 26th Feb 2020, 4:37 pm   #5
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

I've heard that of testing to see of a 'phone case is Diakon is to rub a hidden part with meths as this will soften it but not ABS.

Now a trick for fixing ABS is to soften it with acetone and then press the bits together until it evaporates. I'm wondering if meths could be used in the same way on Diakon. This is just an idea; I've never had a Diakon 'phone so have no experience to go off.
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Old 26th Feb 2020, 5:11 pm   #6
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

Does Diakon "take" to superglue?
If it does then use the super low viscosity one and it should wick into the crack.
There are lots of things that superglue will not bond, that said...
It likes bone for instrument bridges and nuts, it likes most rubber. It doesn't usually like shiny plastics but Diakon might be different.

I didn't know it's composition until now.

https://www.britishtelephones.com/diakon.htm

Last edited by Jon_G4MDC; 26th Feb 2020 at 5:17 pm.
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Old 26th Feb 2020, 5:26 pm   #7
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

Thanks everyone.

The crack is about 3" long and the bits either side can be flexed back and forth to allow access to the surfaces of the crack.
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Old 26th Feb 2020, 5:28 pm   #8
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

“Plastic Weld” as used by modellers may well work if the material is of a styrene or “Perspex” type. It is usually “wicked” into a reasonably tight joint, don’t get it onto visible surfaces.

Ken
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Old 26th Feb 2020, 6:11 pm   #9
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

Yes, thanks Ken, but it's the not getting on the visible surfaces that concerns me. Any suggestions?
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Old 26th Feb 2020, 6:54 pm   #10
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

You may have already seen it but this rather lengthy document describes everything anyone might ever want to know about Diakon:

http://lucitediakon.com/wp-content/u...cal-Manual.pdf

Page 69 gives advice regarding adhesives and it would seem that super glue is the stuff to use. Regarding contaminated surfaces, if you're quick a wipe with meths does work. Even then a white haze may remain depending on the material being glued. However this can usually be removed with plastic polish. Tensol is the other alternative but I've no experience of using it.

Alan

Last edited by ajgriff; 26th Feb 2020 at 7:07 pm. Reason: Additional Info
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Old 26th Feb 2020, 6:59 pm   #11
G6Tanuki
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

There's a two-part "stuff" you can get from car-parts-suppliers intended for repairing split/cracked bumpers.

https://www.eurocarparts.com/p/tripl...28ml-542771340

Cheap enough to be worth giving it a go?
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Old 26th Feb 2020, 7:26 pm   #12
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

For the concerns about getting excess glue on the outside surface, how about putting a strip of airtight / waterproof tape over the crack on the outside and then running the glue / compound into the crack from the inside surface? If done right, that will confine the glue or compound to the environs of the crack and will prevent it from getting onto the outer surface.

Of course you also need to choose a type of tape which the repair substance doesn't stick to too well, otherwise you will end up with a narrow stripe of tape stuck along the line of the repair.
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Old 26th Feb 2020, 7:48 pm   #13
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

I would suggest closing the crack as tightly as you can with a thin strip of tape on the inside, at the start end. The aim is not to create another narrow gap on the outside between any tape and surface, that the solvent can wick into. Then with it as vertical as possible (awkward, I know), put a drop or two of plastic weld (I use a posidrive screwdriver as the pick up tool) onto the inside of the crack. It will wick in very quickly and weld the sides of the crack where they are closely mated. Surplus will evaporate very quickly. The weld will take several hours to harden. Polishing will usually remove any accidental overspill marks but allow plenty of hardening time first.
I have used tensol on acrylic bonding, very successfully but you only get one chance at positioning things and I don’t know about treating cracks. I think it is expensive too, plastic weld is cheap.

HTH

Ken
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Old 26th Feb 2020, 9:40 pm   #14
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

You could try some Bondic, this works well with plastics...but not sure about 1959 ones....plenty of time to position as it only sets when you fire UV light at it then it sets quickly. (UV led fob supplied in kit)
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Old 2nd Mar 2020, 11:22 pm   #15
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

Thanks for the wonderful response everyone, I really appreciate all the ideas.

I bit the bullet and drilled a 3mm dia hole at the terminus of the crack, then countersunk each side fractionally using a countersink bit in my fingers.

Next, I cleaned the crack by "flossing" a strip of thin, slightly damp, cotton cloth back and forth along it, from the start to about 1/2" from the hole I'd drilled. A lot of muck came out, confirming my thoughts that it was a historic crack rather than something that had happened in the post on its way to me.

I then masked the outside of the drilled hole with a bit of Sellotape and dripped some Araldite into the hole from the back to fill it. Hopefully, it should look reasonable with a dab of red paint on it after polishing.

I closed the crack by tensioning a couple of long cable ties around the periphery of the case, then used a large rosehead steel bur in my Dremel (at very low speed) to create a slight trough along the length of the crack, on the inside of the case.

After checking the alignment by running a fingernail over the crack on the outer surface of the case, to detect any "steps", I sparingly drizzled a bit of Tensol into the trough on the inside, using a syringe supplied with the kit, allowing it to be drawn into the crack by capillary action.

I will report back tomorrow when it's hopefully "set".
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Old 3rd Mar 2020, 9:00 am   #16
wireless_john
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Default Re: Ideas for stabilising a crack in a Diakon GPO 706 telephone

Quote:
Originally Posted by Bazz4CQJ View Post
You need to drill a small hole just ahead of the crack, When the crack hits the hole it will stop. I was told about this many years ago and have successfully used this method on a number of items, e,g, aluminium castings, plastic wheelie bins. A hole of 2 or 3mm should be ok.

B
I too have done this. Stopped a crack in my motorhome shower tray!

John
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