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Old 1st Apr 2022, 8:35 pm   #1
qtronix
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Default Had a go at making a new back panel.

i have a ferranti radio that i restored a while back. but the back plate always bugged me how bad it was.
so i had a go at cnc a new back. its not perfect as i done the cad drawing a bit quick, but it works and a lot better then the other one. i used 3.6mm plywood as it was all they had at b-q.
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Old 1st Apr 2022, 10:55 pm   #2
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Default Re: Had a go at making a new back panel.

Looks fine to me !!!.

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Old 1st Apr 2022, 11:00 pm   #3
Cruisin Marine
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Default Re: Had a go at making a new back panel.

Nice work
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Old 2nd Apr 2022, 5:21 am   #4
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Default Re: Had a go at making a new back panel.

That's brilliant! Well done. Now how about scanning the artwork or labels on the original, if there were any, and printing it out to complete the look?

You can include a restoration date and signature too, for when your memory starts to fade!
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Old 2nd Apr 2022, 6:26 am   #5
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Default Re: Had a go at making a new back panel.

When cutting thin ply, if you have a sacrificial lump of something like MDF clamped to it, your saw won't pull those tears off of the outer ply along the edges. The MDF supports the outer ply layer and forces it to cut cleanly rather than tearing fibres off. For really thin stuff, you cut it clamped between two such spelch blocks.

This also works when you're cutting things out with a router

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Old 2nd Apr 2022, 7:39 am   #6
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Default Re: Had a go at making a new back panel.

A lot nicer than the old hardboard one, fitted at the factory, I would say.
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Old 2nd Apr 2022, 1:01 pm   #7
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Default Re: Had a go at making a new back panel.

Quote:
Originally Posted by Radio Wrangler View Post
When cutting thin ply, if you have a sacrificial lump of something like MDF clamped to it, your saw won't pull those tears off of the outer ply along the edges. The MDF supports the outer ply layer and forces it to cut cleanly rather than tearing fibres off. For really thin stuff, you cut it clamped between two such spelch blocks.

This also works when you're cutting things out with a router

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Old 4th Apr 2022, 8:01 pm   #8
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Default Re: Had a go at making a new back panel.

I’m loving the “spelch” blocks LOL

The radio back looks fantastic

Thanks
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Old 5th Apr 2022, 3:23 pm   #9
David G4EBT
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Default Re: Had a go at making a new back panel.

That looks excellent - CAD and a CNC router takes all the laborious work out of using a hand router in a jig, which is how I've made my replica backs over the years. When it comes to making an authentic replica back panel for a radio to replace a missing one (rather than damaged) , the first challenge is to get a 'rubbing' of a good one. Not always easy.

You've done really well to make it from DIY store plywood because it's all low grade largely softwood plywood with lots of voids and surface imperfections. MDF or Hardboard is a better bet, or 'proper' plywood as we once knew it, which is 'BB' grade 'birch through and through'. Larger thickness of 'BB' plywood (EG 18mm) are sold at B&Q at a sky high price, but that's not relevant to this thread.

Their normal range of B&Q (and other DIY store) plywood is often advertised as 'hardwood'. In reality, it has a thin hardwood veneer which makes it look presentable, but the core is poor quality with lots of voids. I suspect the core is softwood, which is usually made either of cedar, Douglas fir, or spruce, pine, and fir (collectively known as spruce-pine-fir or 'SPF'), or redwood. Typically used for general building, roofing or concrete formwork where its mechanical function is more important than its appearance.

You can buy good quality birch plywood suitable for radio backs from the likes of Hobbies Ltd.

A 600mm x 300mm (2' x 1') sheet of 3mm birch ply is £3.90, but of course carriage costs make it impractical:

https://www.hobbies.co.uk/quality-bi...SABEgI8V_D_BwE

By far the best material I've used over the years is oil-tempered hardboard, which machines really well. Some years ago the local B&Q had a batch but I think it must have been a one-off because when I went back for more, they had none, and even the timber merchants don't seem to stock it locally.

Oil tempered hardboard is impregnated with special oil which is polymerised by heat treatment during the manufacturing process. This treatment gives the board increased moisture resistance properties and higher bending strength values. Typical end uses include internal wall or roof linings, signs, facias and flooring underlay:

https://www.lathamtimber.co.uk/produ...tm_source=bing

Not much help to the likes of us who just want a small sheet now and then.

I've been very pleased with the A3 size 3mm MDF sheets I mentioned is this recent forum thread:

https://www.vintage-radio.net/forum/...d.php?t=189440

Link to the sheets:

https://www.amazon.co.uk/Blank-Sheet...088RBWQV4?th=1

As David, 'Radio Wrangler' points out, if using a plunge router on ply, there's a risk of spelching on the lower surface when the bit breaks through unless a sacrificial piece of MDF, hardboard or whatever is used to support the underside. I guess you can program a CNC router to stop when it reached the underside, which is rather tricky to set on a hand plunge router.

Most 'millboard' radio backs - certainly from the immediate post-war years - seem to me to have been made from layers of thick paper from recycled newsprint. I say that because when delaminated, the paper has a greyish colour consistent with re-pulped newsprint, often used for paper and card packaging. Adequate for the job, but not spectacular. Easy to forget that well into the late 1940s, timber and timber products were scarce and were rationed. They wouldn't have bothered to remove the newsprint ink from the pulp unless the paper was used again for newsprint.

As an aside, when it came to timber for furniture, people who were re-housed due to bomb damage and newly-weds setting up home were given priority, and a lot of constructional timber was needed for rebuilding. (Hull - not Coventry or London - was the most war-damaged city in Britain - 95% of houses were damaged in the Hull Blitz. Under air raid alert for 1,000 hours, Hull was the target of the first daylight raid of the war and the last piloted air raid on Britain).
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Old 7th Jun 2022, 7:41 am   #10
Phil G4SPZ
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Default Re: Had a go at making a new back panel.

That looks excellent!

I once made a new replacement for the missing back of a round Ekco AD75 out of hardboard using a manually-guided router. It looks great, but it took me a whole weekend to make! I was lucky to receive a good ‘rubbing’ from a Forum member which helped a lot.
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