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Old 17th Jun 2019, 3:28 pm   #1
G6Tanuki
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Default Refixing meter glass.

I've got a 1940s-era milliammeter made by General Electric - the glass has come detached from the bakelite casing.

In the past I would have reattached it using "Durofix" but my remaining tube of this has gone hard in the decade and a half since I bought it, and Durofix doesn't appear to still be available (banned because of its high aromatic-solvent content?).

What to use ?? - I'm reluctant to use modern superglue as I fear it may set too 'hard' and increase the risk of the 70-odd-year-old piece of glass cracking.
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Old 17th Jun 2019, 3:44 pm   #2
Andrewausfa
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Default Re: Refixing meter glass.

I used black Roof & Gutter sealant on an AVO once. Not too expensive at a couple quid a tube.

Andrew
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Old 17th Jun 2019, 3:53 pm   #3
The Philpott
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Default Re: Refixing meter glass.

Araldite. There's two grades of curing, the red packaged one takes minutes, the blue takes hours. I usually use the red unless it's a fiddly job.

Even if you apply a little too much and it smurges onto the front of the glass, it doesn't set rock hard so can be scraped off when semi-cured quite easily. I have only ever had one glass crack, and i think that was because i applied Araldite around the EDGE of the glass as well as the front face. This appeared to set up stress when it cured.

I would say that if you ever have to remove an araldited glass though, it does put up a fight. For this reason i tend to use quite small amounts, blobbed on at strategic points.

On the rare occasions i use superglue, it is when the glass feels secure, but viewed from inside the meter the contact area of the old glue doesn't seem large enough. In this case the wick effect of cyanoacrylic is an advantage. The one proviso is waiting until the glue is utterly dry before reassembling the meter, as it can creep across dirt or fingerprints on the surface of the glass and fog it. (Cure- acetone based nail varnish remover)

I recall that Micheal recommends making up a black putty so that glass can be removed easily in future if required. I have never tried this approach.

Dave
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Old 17th Jun 2019, 4:19 pm   #4
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Default Re: Refixing meter glass.

Clear silicone sealant worked fine me.
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Old 17th Jun 2019, 4:42 pm   #5
G6Tanuki
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Default Re: Refixing meter glass.

Thanks for the suggestions! I've gone with clear silicone (a variety that's supposed to be mould-resistant). Will see how well it's worked in a day or so once it's cured and the vinegary smell has dissipated.
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Old 17th Jun 2019, 8:22 pm   #6
The Philpott
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Default Re: Refixing meter glass.

That should work; and I don't know why it hasn't crossed my mind before. Once the acetic acid has dispersed it should be inert.
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Old 18th Jun 2019, 12:30 am   #7
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Default Re: Refixing meter glass.

Durofix was aiui a cyclohexane contact adhesive and these are still universally available. I keep a tube in stock at all times, either Uhu or Wickes High Strength Contact Adhesive
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Old 18th Jun 2019, 12:47 am   #8
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Default Re: Refixing meter glass.

PVC pipe glue is quite good on quite a few things.
The problem is that it is a bit smelly.
I had some left over after fixing a drain.
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Old 18th Jun 2019, 1:18 am   #9
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Default Re: Refixing meter glass.

I use non-acid cure black silicone rubber for this task. It takes a long time to set at least 24Hrs. It is important to make sure it is applied everywhere to get a seal, or dust and atmospheric contaminants can enter around the perimeter where the glass is not perfectly approximated to the housing surfaces. Excess is easily wiped off the class with a lint free cloth soaked with some meths.
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Old 18th Jun 2019, 1:19 am   #10
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Default Re: Refixing meter glass.

I use roof and gutter silicon sealant too. It does not contain the smelly acetic acid. I have wondered whether it would eat the varnish off the very sensitive enamel used on the coil.

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Old 18th Jun 2019, 9:15 am   #11
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Default Re: Refixing meter glass.

Quote:
Originally Posted by Refugee View Post
PVC pipe glue is quite good on quite a few things.
The problem is that it is a bit smelly.
I had some left over after fixing a drain.
I thought PVC pipe glue (cement) was a solvent? It dissolves the mating surfaces effectively welding them together when they resolidify. It won't have much effect on glass.
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Old 18th Jun 2019, 9:52 am   #12
pmmunro
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Default Re: Refixing meter glass.

There is a grade of Araldite specifically for bonding glass.

https://www.go-araldite.com/products...l-2-x15ml-tube

PMM
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Old 18th Jun 2019, 10:05 am   #13
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Default Re: Refixing meter glass.

I use RTV silicone 732 as its black and works very well
plus we use it at work
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Old 18th Jun 2019, 11:51 am   #14
micheal
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Default Re: Refixing meter glass.

Putty mixed with a little oil based black paint, looks similar to original and glass can be easily cleaned afterwards with white spirit.
If glass ever gets broken can be easily replaced.

mike
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Old 19th Jun 2019, 1:19 pm   #15
G6Tanuki
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Default Re: Refixing meter glass.

All back together now, and working just fine.

Speaking to someone else who fixed a similar meter I'm glad I didn't use superglue: on his one the superglue 'crept' across the interface between the glass and the meter-case until it found the set-zero adjuster (which lives between the glass and the case) with predictable and unsalvageable end-results.
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Old 24th Jun 2019, 11:22 am   #16
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Default Re: Refixing meter glass.

Quote:
Originally Posted by Argus25 View Post
I use non-acid cure black silicone rubber for this task. It takes a long time to set at least 24Hrs. It is important to make sure it is applied everywhere to get a seal, or dust and atmospheric contaminants can enter around the perimeter where the glass is not perfectly approximated to the housing surfaces. Excess is easily wiped off the class with a lint free cloth soaked with some meths.
It would be a better choice to use IMS (industrial methylated spirit, denatured alcohol) as it doesn't contain any dye, which could smear on the glass. Maybe even a drop of vodka?
Colin.
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