Knob repair… what glue?

[HoverJohn]

So due to my family’s ability to hoard I’ve found the 2 halves of the missing knob off the Dynatron- but what glues are effective on these old plastics? It’s not Bakelite as the arrow on the top looks to have been hot moulded in afterwards?

Quite impressive seeing as it’s been bust off since the 70s at least -

I also need to re-fill the arrows with gold paint- what sticks (evidently not the original one.)

[ajgriff]

I suspect it is bakelite. Whatever it is plain old superglue should work well especially with the rough edges of the break. Just make sure that the edges to be joined are really clean. Give them a good scrub with an old toothbrush and meths or whatever cleaning agent you favour. Wipe off any excess glue with meths before it hardens.

Since the gold is recessed I'd use acrylic water colour for the paint which will make it easy to clean up any excess. It's quite durable when dry.

Alan

[Goldie99]

It looks as though there may be part missing as well (?) - if so, I'd probably opt for a 2-part epoxy (Araldite is my favourite), but also echo Alan's comments re. cleanliness - the cleanliness of surfaces to be glued is one of the most critial aspects to achieving a good and long lasting bond, whatever the adhesive.

If there are part(s) missing, I'd probably also apply a later, second, lot of epoxy to add reinforcement as appropriate (after the first had set obviously).

Alan

[stevehertz]

Clean the fractured areas with IPA using a stiff brush. Re-join them using thin superglue. Then on the underside, reinforce the area around the join with a good fillet of Araldite, having previously made sure that that area has also been cleaned with IPA. That'll do it.

[Richard]

Hi

Looking at the pictures you are missing the metal collar with the grub screw thread, and the grub screw.
I would tape the 2 halves together and then fill the recess around the centre tube with 2 part epoxy.
Then you can drill a new grub screw hole in the resin and tap a thread into it, a longer grub screw would help since the thread is now in resin.

Richard.

I would (and do) use Araldite Precision, takes a day to set and is super sticky. As is said, longer is stronger.

[G6Tanuki]

Yes there should be a metal bush that fits in the centre hole. You may be able to make something up by cutting-down a 1/4-inch spindle-coupler and turning it to be a snug fit in the centre ghole of the knob.

Then use superglue or similar to join the two halves of the knob back together. Then. as suggested above, fill the recess completely with Araldite, JB Weld or simlar - then use ssame to fit the replacement metal bush to the centre hole.

[Andrew B]

I would use a quality superglue gel with a "Zapper", a spray on instant accelerator, model aircraft type shop will supply you. They are a heaven for specialist adhesives.

[HoverJohn]

Ok yes I have the collar it was still on the spindle it appears it was pressed into the knobs after as it’s not encased. Is there any way to test if it’s Bakelite it looks thermoplastic as the arrow mark seems to have been hit moulded after.

[ajgriff]

Does it matter? The material is clearly hard and brittle so any of the products already mentioned should be effective. If you're really worried about an adverse reaction test with a small spot on the base.

Alan

[The Philpott]

For my money, cyanoacrylate superglue is far too quick for this job. I like to frown at the repair and double check it, and for this you need more time. As the piece has actually broken apart and the broken surfaces are easily accessible, Araldite every time. It's not an F1 pitstop, after all.

I only use superglue when the crack/s haven't opened up; as it is able to wick in.

As for gold paint i suppose Humbrol Enamel (for modellers) would be best...?

Dave