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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 4th Mar 2005, 11:42 pm   #1
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Default Best Adhesive for Iron Dust Core?

I have the usual problem of an iron dust core that has become detached from the screwed brass rod. Just to make things worse the core has split longways into three pieces.

What's the best adhesive for gluing the bits together and reattaching it to the screw?

Graham.
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Old 5th Mar 2005, 12:12 am   #2
ukcol
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Default Re: Best Adhesive for Iron Dust Core?

Hi Graham

I have successfully re-attached the screws to the iron dust cores in an Invicta 65. I drilled out a 'cup' in the top of the cores first to increase the contact area and then used two-part epoxy resin adhesive (not the fast setting type). The repair survived an IF realignment and is still OK after 2 years service.

I don't think your split cores could be done by this method as the resin takes up too much room and the cores would not fit into the coil formers. Perhaps the splits could be dealt with using super glue and the screw threads attached using the above method.
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Old 5th Mar 2005, 10:42 am   #3
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Default Re: Best Adhesive for Iron Dust Core?

Colin.

This particular core is a hollow cylinder, so I don't anticipate any problems in attaching it to the threaded brass rod. I'm not keen on superglue for gluing the core together. It's very fiddly lining up the bits and I might get them stuck together in the wrong position, or stick my fingers to it.

I could try taping the bits together and then using two part epoxy to glue in the threaded rod. This should hold all three parts to the rod.

The core has been snapped because someone (not me) has tried to unscrew it the wrong way. They've turned the screw so hard that the slot has been mutilated. It a miracle the former hasn't broken and destroyed the coil.

Graham,
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Old 5th Mar 2005, 5:29 pm   #4
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Default Re: Best Adhesive for Iron Dust Core?

Hi Graham

I agree that super glue is difficult to work with and only works well when you have simple clean breaks. Its fortunate that the cores are hollow allowing you to use epoxy. Let us all know how you get on.
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Old 12th Mar 2005, 9:44 am   #5
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Default Re: Best Adhesive for Iron Dust Core?

The adhesive I used was "Araldite Precision". This has a very long setting time and comes in a dual syringe package. I stuck the three parts of the core together and used two rings of twisted copper wire to hold them in tight contact. The core was placed in a warm place to set and after 16 hours I removed the wire rings and scraped off the excess adhesive.

When I tried to remove the screwed rod from the coil former it wouldn't move far, as the thread had been damaged. I recut it, not without difficulty, with a 4BA die and was able to remove it. A new screw slot was cut in the end with a junior hacksaw and the die run down the whole length of the thread.

The core was gently clamped in a lathe chuck and progressively larger drills run through it until the surplus adhesive had been removed. The core has a step in the bore, so the large end was further drilled out until the grooved cylinder on the end of the screwed brass rod would just enter.

The screwed rod was then glued into the core. I held the rod in the tailstock chuck of the lathe to keep everything in alignment. The use of a lathe may be regarded as overkill and I could have managed without it, but I decided to use it though as it made the job quicker and easier.

Once the adhesive had cured I removed the assembly from the lathe and refitted it to the coil former. The core was originally "locked" by a spring clip, which I think may have contributed to damaging the thread. I decided to use a 4BA locknut instead.

Having fixed the damaged core aligning the set was easy.

Graham.
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