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Old 29th Sep 2020, 3:17 pm   #1
Boulevardier
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Default Glueing stainless steel to (old) plastic

I have a 1980s Soviet radio (Selena B-215) on which the plastic chassis is becoming old and brittle (common story). I need to glue some internally threaded stainless-steel sleeves into the original plastic mouldings which fasten the main chassis to the front panel (the original threads in the plastic have stripped). I'm going to drill them out to the external diameter of the SS sleeves, which will then need glueing in place. Anyone have any tips as to the best adhesive to use for this (I need a bit of time before setting to ensure alignment is OK)? I'm thinking two-part epoxy. I'm not sure what plastic formulation the soviets are likely to have used back in the 80s - judging by the construction elsewhere in the set, about 10-20 years behind the West!

Any tips appreciated!

Mike
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Old 29th Sep 2020, 3:21 pm   #2
paulsherwin
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Default Re: Glueing stainless steel to (old) plastic

I agree that good quality epoxy is your best bet. Don't use the Poundland stuff. I use 'classic' slow setting Araldite for these sorts of jobs (marketed as 'Araldite Precision' I think) but others will have different preferences.

The B21x series is certainly a bit of an oddity, a strange combination of overdesign and shonky construction.
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Old 29th Sep 2020, 4:01 pm   #3
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Default Re: Glueing stainless steel to (old) plastic

Just to add what Paul has said , score the ss sleeves this gives the glue something to grab hold of . Mick.
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Old 29th Sep 2020, 4:31 pm   #4
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Default Re: Glueing stainless steel to (old) plastic

Thanks, yes I've been thinking about scoring the sleeves and the plastic surface. I'm a bit worried about the "piston" effect of inserting the sleeve, and that it will force adhesive up inside the internal threads in the sleeves, and scoring would hopefully also avoid this by allowing the adhesive to escape (if it has to go somewhere) up the channels created by scoring. The slow setting is important as all four sleeves will carry pillars that have to be carefully aligned to go through the main pcb and the back panel - the pillars that screw into the sleeves are about 3 inches long, so a small angular error can prevent everything lining up when assembled. So the Araldite sounds just right to allow the time to get any adjustment of the pillars done.

Mike
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Old 29th Sep 2020, 5:27 pm   #5
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Default Re: Glueing stainless steel to (old) plastic

Keep the Araldite cool before use - that will help slow it down. Also, make sure the surfaces are scrupulously clean. If possible, acetone or MEK on the stainless, but only IPA on the plastic.

I've heard some very positive comments about the American "JB-Weld" 2-part epoxy, but don't personally have enough experience of it to compare it with Araldite.

B
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Old 29th Sep 2020, 5:27 pm   #6
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Default Re: Glueing stainless steel to (old) plastic

Quote:
Originally Posted by paulsherwin View Post
The B21x series is certainly a bit of an oddity, a strange combination of overdesign and shonky construction.
"Oddity" is the word, and this is pehaps the most visibly odd thing about mine -
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Old 29th Sep 2020, 6:33 pm   #7
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Default Re: Glueing stainless steel to (old) plastic

Quote:
and that it will force adhesive up inside the internal threads in the sleeves
You can dig that out when the adhesive becomes rubbery, a small pair of tweezers and a twist usually does the job.
 
Old 29th Sep 2020, 8:36 pm   #8
ex seismic
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Default Re: Glueing stainless steel to (old) plastic

Or run a plug tap down the sleeves. Araldite will tap quite happily.
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Old 29th Sep 2020, 11:57 pm   #9
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Default Re: Glueing stainless steel to (old) plastic

Are you sure about stainless steel bushes? THreaded parts do tend to gall in them, so brass might be a better alternative if they don't show.

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Old 30th Sep 2020, 12:22 am   #10
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Default Re: Glueing stainless steel to (old) plastic

Just checked orders (I had to place separate orders to get suitable lengths to try out). One lot is ss according to the eBay ad, and the other lot are zinc. I don't know what " gall" means. Could you explain? (sorry if it's just a typo!).

Mike
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Old 30th Sep 2020, 2:05 am   #11
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Default Re: Glueing stainless steel to (old) plastic

Gall or galling can be thought of as a kind of "friction welding" and the main place most people get to see it is if they use stainless steel screws with stainless steel nuts. What often happens is as they are tightened, the surfaces gouge in to each other, and at that point it is really hard to either tighten them further, or to undo them.

The easiest way to avoid galling is just to use different materials (stainless + brass). Otherwise, generous lubricants may help, as may Teflon tape.

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Old 30th Sep 2020, 6:55 pm   #12
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Default Re: Glueing stainless steel to (old) plastic

Thanks for that Bazz. I hadn't heard of this before. The other pillars I've ordered are advertised as "Zinc", so presumably plated. I will probably use those.

For a radio that I considered as "marginal" in terms of worthwhileness, this Selena is starting to get a bit demanding in terms of component repair and physical rebuild time and cost.

Mike
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Old 30th Sep 2020, 7:08 pm   #13
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Default Re: Glueing stainless steel to (old) plastic

If you're worried about the adhesive passing up inside the threaded sleeve, get a screw or length of studding that's the required thread, coat it with Copaslip, then screw it into the sleeve until it's level with the end-of-the-sleeve-that-will-be-glued-into-the-hole.

After the glue's hardened, you unscrew the screw/stud leaving a nice clean hole.

[This is what we used to do when prepping vehicle-chassis for galvanizing - it's a lot easier than having to tap-out dozens of captive-nuts that have been clagged by the zinc]
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Old 2nd Oct 2020, 1:36 am   #14
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Default Re: Glueing stainless steel to (old) plastic

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If you're worried about the adhesive passing up inside the threaded sleeve, get a screw or length of studding that's the required thread, coat it with Copaslip, then screw it into the sleeve until it's level with the end-of-the-sleeve-that-will-be-glued-into-the-hole.

After the glue's hardened, you unscrew the screw/stud leaving a nice clean hole.

[This is what we used to do when prepping vehicle-chassis for galvanizing - it's a lot easier than having to tap-out dozens of captive-nuts that have been clagged by the zinc]
Thanks. Even a small container of Copaslip is a bit "overkill" - I'll only need about half a teaspoonful max for this job. Is there a more everyday alternative for coating protection from the Araldite Standard ? Vaseline, grease, etc? Even clingfilm (which will never be seen once glued)!

Not to be penny-pinching - just practical - and not to accumulate stuff, 99% of which will never get used again and will end up in landfill.

Mike

Last edited by Boulevardier; 2nd Oct 2020 at 1:55 am.
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Old 2nd Oct 2020, 8:46 am   #15
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Default Re: Glueing stainless steel to (old) plastic

Vaseline will work too, I have used it for similar non-glue requirements.
 
Old 2nd Oct 2020, 9:37 am   #16
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Default Re: Glueing stainless steel to (old) plastic

Personally I would have used brass, far easier to work with, and much kinder to the screws that go into it.
Mike
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