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Old 15th Apr 2018, 2:37 pm   #1
1960tvr
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Default Roberts RT1 radio

On this radio is the clear dial faceplate glass or perspex? On mine it is perspex and I thought that might be a later addition seeing it's a '58 radio. Anyone have any views?
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Old 15th Apr 2018, 3:45 pm   #2
Paul_RK
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Default Re: Roberts RT1 radio

It's perspex, even on Roberts models rather older than the RT1: at least as far back as the 1946 P4D and P5A, while earlier sets I think used celluloid rather than glass.

Paul

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Old 16th Apr 2018, 11:50 am   #3
1960tvr
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Default Re: Roberts RT1 radio

Thank you for information I am quite surprised. Any ideas on how to polish the surface as it is dull and a lot of fine scratches which stop it from being clear or will I have to source some new Perspex?
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Old 16th Apr 2018, 1:31 pm   #4
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Default Re: Roberts RT1 radio

I generally put the panel on a flat surface, so it won't be flexed at all, and use a reasonably gentle liquid metal polish - Silvo or Brasso - on a rag. Takes some persistence and elbow grease and won't remove any deep scratches, but the fine sort caused by general wear should more or less vanish.
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Old 16th Apr 2018, 1:56 pm   #5
David G4EBT
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Default Re: Roberts RT1 radio

Really, though it's tempting to use silver polish, 'T Cut', Bakelite polish and the like, it's more likely to make matters worse - not better. you'd need to use something like 'Xerapol' Perspex polish which you can obtain here, but it would cost more than a new piece of Perspex so if you have the skills and equipment to cut it to size using the old one as a template, I think that would be a better option:

https://www.theplasticshop.co.uk/per...h-xerapol.html

If you did want to make a new dial, don't for goodness sake attempt to drill the holes for the control shafts with normal engineering drill bits or as sure as anything it will snatch the sheet and crack it. Instead, uses a 'step drill' sometimes called a 'cone drill'.

Perspex is acrylic sheet, but there isn't just one type and 'Perspex' has become a generic term like 'Thermos', 'Hoover' etc. Which type you choose depends on how much you are prepared to spend. Firstly, there's 'cast' acrylic sheet which offers near perfect optical clarity, and secondly, there's 'extruded' acrylic sheet, which is cheaper, and I'm sure would be quite adequate.

Personally, if you do consider making a replacement dial, I'd search for 'clear acrylic sheet' - if you search for genuine 'Perspex' you may get a shock at the price.

I use clear acrylic sheet quite a lot for front panels of my homebrew projects, and buy the smallest sized sheet of glazing acrylic from B&Q or wherever. I'm sure that an eBay search would turn up something at a sensible price, and you can buy a 3mm thick A4 sized sheet from Amazon for 2.39 post free here, which would be large enough for your needs and you might even have enough for two attempts:

https://www.amazon.co.uk/Clear-Acryl...X8P7P6G4J6G27D

Hope that helps a bit.

Good luck in your endeavours.
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Old 16th Apr 2018, 5:34 pm   #6
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Default Re: Roberts RT1 radio

Hello David,

I too would fight shy of bakelite polish for a clear acrylic window, expecting its abrasive effect to be too coarse, and I've never actually met any T-Cut, but after your post I thought I should make quite sure that my memory of using Silvo in such an instance isn't a false one. So here's the central part of an RT1 dial after ten minutes' vigorous polishing of the perspex cover: I've only refrained from including a "before" image because it wasn't sufficiently different, as I expect the set received a similar treatment way back when and hasn't had any rough usage since.

Fine scratches are dealt with, deeper ones may not be helped much or at all, but I really don't think that polishing with liquid Silvo on a soft cloth runs any risk of making matters worse, at least provided the formulation hasn't changed dramatically since I bought my litre can of it donkey's years ago. If it doesn't produce a sufficient improvement the option of making a new window of course remains.

Paul
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Old 16th Apr 2018, 7:08 pm   #7
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Default Re: Roberts RT1 radio

I'm pretty sure that the main ingredient in Xerapol, as recommended by David in post 6, will be cerium oxide. If so, it can be bought economically as a dry white powder which when mixed with a little water becomes a smooth paste.

People have written books about abrasives but the key thing about cerium oxide is that the particles are smooth rather than jagged lke those of silicon carbide. Both of these are extremely hard abrasives but the oxide has less of a tendency towards scratching the surface to which it's applied.

Alan
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Old 16th Apr 2018, 7:52 pm   #8
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Default Re: Roberts RT1 radio

Your dial looks fine Paul.

Re Xeropol, here's what the supplier says about how to apply it and how it works:

Quote:

How is the Perspex polish applied?

Clean the surface and apply a little polishing paste. Using a soft, clean cotton cloth or pad, polish the scratched areas using heavy pressure for 2-3 minutes. For deeper scratches repeat application several times. Remove residue with a cloth. Very deep scratches should be treated beforehand with the special super-fine (granularity: 1600) abrasive paper and a little water, then treated as above.

Do not use on printed, varnished or coated surfaces. Not suitable for polycarbonate or other materials. If in doubt, or for further advice - please contact us.

How does Perspex polish work?

The Perspex surface is lightly dissolved and polished with fine abrasive particles. During polishing, the edges of the scratches are rounded off and the fissure bottom is filled in. This returns the Perspex acrylic surface to its former smooth and shining glory.

End quote.

Their words - not mine!
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Old 16th Apr 2018, 7:55 pm   #9
1960tvr
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Default Re: Roberts RT1 radio

Thank you all for your kind advice on the subject which I have taken on board.I will try the 1st option of trying to polish out the scratches and see how it goes,I have nothing to lose. If this does not work then I will try cutting a replacement out.I will keep you all posted with the outcome. Many thanks to you all for taking the time to reply.
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Old 16th Apr 2018, 8:22 pm   #10
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Default Re: Roberts RT1 radio

Still think Xerapol is largely cerium oxide and water although the marketing blurb's reference to 'dissolving' the surface is interesting. Acetone is the most likely candidate but the amount must be very tiny or a horrible mess would ensue. It also evaporates quickly so I doubt if it does much in reality.

Alan
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Old 16th Apr 2018, 8:26 pm   #11
1960tvr
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Default Re: Roberts RT1 radio

Further to the advice on how to remove scratches on perspex I found some turtle wax scratch removal in my garage and chanced giving that a try because I had no metal polish.I placed it on a hard worktop and did a backward and forward motion for 10 minutes on both sides and it really brought it up like new,well please with outcome and advice given by you all and your knowledge. Many thanks
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