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Old 3rd Jun 2019, 3:05 am   #1
Boulevardier
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Default Distorted plastic tuning scale

This scale (7.8cm x 4cm) is from a small transistor "world" radio. It is on soft plastic and has no panel behind it when mounted. It has become distorted over the years - so much so that it is fouling the straight wire pointer that sits above it. It is held in place in small slots in plastic pillars - one at each corner. The plastic scale is about 4mm thickness, and there wouldn't be room to fit a stiffening panel behind it. I'm trying to think of a way to get it back to its flat original shape without damaging it. I wondered if applying a cool-ish iron to the back would do the trick - but I don't want to damage it further with the heat. Any thoughts?

Mike
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Old 3rd Jun 2019, 4:49 am   #2
joebog1
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Default Re: Distorted plastic tuning scale

Depending on how old it is, it may even be nitro cellulose. I wouldnt be using an iron on it.
Its easy to test though, cut a tiny bit from somewhere it wont be noticed ( perhaps behind the front fascia) and see if it burns.
I would try and make a thin stiff aluminium backing plate with cutouts to fit the plastic pillars, then using a non volatile glue ( acrylic contact, water based, for example ) glue it to the backing plate using a very flat "press face" against the plastic, and sit a brick or two on top of it to press it flat. Acylic contact wont let go in the future either!!

A further thought would be to place the dial scale on a piece of glass, apply glue to the aluminium plate and place that on the top of the scale ( back to front of course), THEN apply the bricks.

Just my take

Joe
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Old 3rd Jun 2019, 5:50 am   #3
Lloyd 1985
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Default Re: Distorted plastic tuning scale

Maybe sandwich it between 2 sheets of glass and warm it with a hair dryer? I think an iron might be too aggressive on that type of plastic.

Regards
Lloyd
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Old 3rd Jun 2019, 9:56 am   #4
Boulevardier
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Default Re: Distorted plastic tuning scale

Thanks - typo in my first post - 4mm should read 0.4mm
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Old 4th Jun 2019, 2:57 pm   #5
PJL
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Default Re: Distorted plastic tuning scale

It won't be nitro-cellulose, probably a plastic. Reminds me of 'Shrinkles' that my children used to colour in and stick in the oven to make miniature badges. Keep an eye on it as heat may make it shrivel up!
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Old 4th Jun 2019, 6:29 pm   #6
line sync
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Default Re: Distorted plastic tuning scale

I`ve had this problem a couple of times on mid to late 30`s radios and would also be interested to here if they can be flattened out.
I`ve tried pouring on very hot water and putting a heavy weight on top until cool but it didn`t work.

Robin
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Old 5th Jun 2019, 1:08 am   #7
Boulevardier
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Default Re: Distorted plastic tuning scale

Seem to have fixed it. I threw caution to the winds and went into battle with an iron. I took it step by step, and started with the lowest setting and a sheet of greaseproof paper between iron and the plastic back. It didn't seem to be harming it (or having much effect), so I gradually increased the temperature and the applied pressure. Got to a point where the plastic was definitely starting to stick to the glass panel below it, and stopped there. Result - job done - flat as a pancake again.

Risky process, and may not help others much - there are so many different formulations of "plastic" - let alone whatever it is they used back in the 40s,50s or 60s.

Mike
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Old 5th Jun 2019, 9:18 am   #8
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Default Re: Distorted plastic tuning scale

Fortune favours the brave! Great result.

Alan
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Old 5th Jun 2019, 4:43 pm   #9
emeritus
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Default Re: Distorted plastic tuning scale

I have a radio that looks like that, bought from Tandy when they were clearing stocks prior to closure. Mine is OK at present, but I will keep this in mind if I have the same problem in the future.
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Old 5th Jun 2019, 4:54 pm   #10
Boulevardier
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Default Re: Distorted plastic tuning scale

The one I have is branded "saisho", and must have been bought about 20+ years ago. Can't remember where... For what it is, and the price (I think about £20.00 back then), it's not bad - conveniently small for travelling, and batteries (just 2 x AA) seem to last forever. Now, that's what I call portable! Couldn't get this battery life on anything made today.

Mike
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Old 5th Jun 2019, 5:12 pm   #11
Boulevardier
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Default Re: Distorted plastic tuning scale

PS the one thing I resent is the insane graphic design of the tuning scale. For FM band it is coloured red/brown on a matt black background - virtually illegible without a bright light + angling to minimise reflection on the perspex front + a magnifying glass. Air Band is actually on the same scale and switch position as FM, which makes sense as they are continuous frequency-wise, but that section is blue on matt black - still pretty taxing on the eyes... Whoever designed that deserved to be shot!

Mike
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