Bakelite cabinet crack re-inforcement

[Dickie]

I am now the proud owner of Lowemission's basket-case (sorry Julian!) Ekco AC76 and am considering how best to treat the crack. See picture in

https://www.vintage-radio.net/forum/...d.php?t=100435

The crack is clean and tight, and having read through all the threads on bakelite crack repair it seems the best thing to do is to run some good quality superglue into it and hope for the best. I have located some supposedly thin superglue for the task but would appreciate any advice from members more experienced than I. The case in this area is only about 3mm thick and I am tempted to epoxy in a metal reinforcing plate on the inside to make sure it doesn't break apart again. Is that worthwhile? Will I get problems with differential expansion of bakelite, epoxy, and metal? I know this will look awful but there is no point in trying to hide the crack.

There's a lot to do on this set and this is going to be the first of many posts. Watch this space!

[mark pirate]

I have used superglue to repair bakelite with great success, I used car fibreglass repair paste to reinforce the rear of the repair, and have had no problems with this method.
I don't think you need to worry about heat in that area of the set.
As yours is a valuable set, I would firstly experiment on a scrap cabinet to find the best/neatest way to do it.

Mark

[Robert Darwent]

Its important to stabilise the crack so it doesn't continue to the front of the cabinet and I've found superglue to be the best thing for that.

Try to open the crack slightly when applying the glue for the best adhesion but take care not to unduly stress the bakelite and make the crack worse whilst doing so.

Often superglue alone will be sufficient do the job but internal reinforcement with epoxy wouldn't hurt either.

I shouldn't worry about expansion issues due to heat, the crack is low enough down for that not to be a concern here.

Regards

[wireful3]

I too have used fibreglass to strengthen the inside. I used the mat rather than the paste but it might not give as neat a finish.

[Robert Darwent]

Originally Posted by Dickie

I am now the proud owner of Lowemission's basket-case (sorry Julian!) Ekco AC76...

I wouldn't call the set a "basket-case" by any means, from the pictures it looks to be in quite a good restorable condition.

Take a look at the bakelite cabinet I had to deal with on my Ekco AD75 set here; Ekco AD75 released c.1940 & 1946 for a real basket-case! But it didn't turn out too bad in the end I think?

By the way, the crack running in the left hand foot (as viewed from the rear) was stabilised with superglue only.

Good luck with your AC76!

Regards

[Dickie]

Thanks gents, it sounds like epoxy or glassfibre putty is the way to go. At least it will be easier to remove if the need ever arises. I have read good reports on Milliput, is it suitable for mechanical strengthening as well as a filler?

That's a good restoration, Robert. I am very impressed. Your phrase " it didn't turn out too bad in the end" is very telling. There's obviously a lot of trial and error and false starts before you get to a good result.

And by the way, 'tis true the cabinet is in one piece, but the rest of the radio had been dismantled and a basket would have been useful to get it all in the car

[Robert Darwent]

Originally Posted by Dickie

Thanks gents, it sounds like epoxy or glassfibre putty is the way to go.

I would try a good quality superglue by itself first and see the result. You may find epoxy isn't necessary.

Originally Posted by Dickie

I have read good reports on Milliput, is it suitable for mechanical strengthening as well as a filler?

I used Milliput to fill the small gaps between the replacement spars and the bakelite on my AD75 after fixing them first with superglue. It sets solid but isn't really strong enough mechanically without some sort of support underneath. Its best used as a filler.

Originally Posted by Dickie

Your phrase " it didn't turn out too bad in the end" is very telling. There's obviously a lot of trial and error and false starts before you get to a good result.

Apologies for my misleading choice of phrase, because there was no "trial and error" of "false starts" involved. I may have been lucky that it happened that way but the repair worked satisfactorily first time. It was a case of thinking about how to proceed to fix the damage more than anything else.

Originally Posted by Dickie

And by the way, 'tis true the cabinet is in one piece, but the rest of the radio had been dismantled and a basket would have been useful to get it all in the car

OK I understand, you needed a "basket" rather than it being a basket-case! Well, working out where everything should go and putting it back together again is half the fun.

Regards

[Dickie]

I have purchased some "Roket Hot super-thin penetrating cyano glue" from my local model shop and am going to try that:
http://www.deluxematerials.co.uk/pages/superglues.htm

The thing that worries me is how do I know if the superglue-only joint is strong enough? I guess if it survives all the polishing stages and putting the chassis in and out several times then it is.

[Lloyd 1985]

Hi,
I've always found bog standard superglue (Loctite's version) does the trick. I apply the glue, let it overflow on the visible side of the crack a bit, hold everything in place until it starts to stick (don't keep pulling it apart to see if it's stuck!) then leave it overnight somewhere warm. Once it's all set nicely I then set about it with VERY fine wet & dry paper, P600 would probably be the coarsest I'd use (although I have used P400 before, it makes more work for yourself.) sand the surface flat, then polish it with your usual Bakelite polish.

On a large cabinet like this I'd probably use some fibreglass on the inside just to give it a bit of extra strength, I've got 2 AC76's in battered conditions, and I've noticed the cabinet's are quite flexible, which could cause the repaired crack to pop open again if it was flexed in the right direction. Saying that, I have used just supeglue on it's own on a few sets and not had any cracks reopening.

If you do need some fibreglass, you can get a kit from Halfords called 'David's Fastglass', which I've used before with success.

Regards,
Lloyd.

[Robert Darwent]

Originally Posted by Dickie

The thing that worries me is how do I know if the superglue-only joint is strong enough? I guess if it survives all the polishing stages and putting the chassis in and out several times then it is.

You've answered your own question there. It's surprising how strong a bond superglue forms with bakelite. We tend to think of bakelite being like a modern plastic when it comes to gluing up cracks, it is not.

Bakelite is porous due to the filler material is contains, usually sawdust, and will happily absorb water if allowed to sit in it too long whilst you are cleaning it to the detriment of the polished finish.

However, with superglue it allows it to seep into the fibrous filler material and form a good bond.

Originally Posted by Lloyd 1985

I apply the glue, let it overflow on the visible side of the crack a bit

I tend to do the opposite of Lloyd and apply the superglue to the inside whenever possible. That way the visible polished side of the cabinet is usually left untouched, with any overflow of glue out of sight on the inside surface.

It's not always possible to avoid applying glue to the polished side though and Lloyd's method of P600 paper or higher and then wax polishing is the way to go on such occasions.

Regards

[Bazz4CQJ]

I'm not sure if this is the best approach in this case, but a technique I've used very successfully on a number of occasions to stop crack propagation is to drill a small hole in the material slightly ahead of where the crack presently stops. If the crack continues to propagate, then when it reaches the hole the stress is the spread over the circumference of the hole and not concentrated in the microscopic crack tip. This method really does work, but is not always attractive when appearance matters.

[Robert Darwent]

Originally Posted by Bazz4CQJ

a technique I've used very successfully on a number of occasions to stop crack propagation is to drill a small hole in the material slightly ahead of where the crack presently stops.

That certainly works and is fine if you intend to fill the hole afterwards and conceal by painting over for example.

But for a bare unpainted bakelite case, especially one for a round Ekco, is not advisable if the monetary value of the set is to be maintained.

Regards