Best Glue for Hard Plastic

[Don]

Anyone know the best cement/epoxy/etc. options for gluing hard plastic? I need to repair the backing disk in a volume control for a Dynaco SCA80 amp. As you can see in photos attached, a square section of the shaft needs to go through a square hole in the disk so it can turn in parallel with the rear pot. Sufficient torque is involved so that the Krazy Glue I tried didn’t hold.
Don

Attachments:

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[John Greenland]

Don;
I have 2 sheets that I copied out of a magazine a few years ago. These 2 sheets give an excellent overview of glues and best uses. I am going to attach them them here. They are over a meg, so I hope that they will attach OK.
If there is a problem with that let me know.

I have no idea if I am in violation of some copyright rule, but I did buy the magazine, so here goes.

Attachments:

1. glues.pdf
2. glues_1.pdf

[Don]

These are great reference sheets, John. I’ve been doing some looking on the web and haven’t found the various combinations summarized as well as these. I had a bottle of Magic Glue, which is a cynoacrylate, that I was sure would do it. But unfortunately it had hardened since I last looked. Interestingly, the other page you posted identifies Krazy Glue also as a cynoacrylate, and it failed when I tried it. I guess the different brands vary a lot in strength. Now if someone can recommend the best brand ….
Thanks again for posting these. I’ll be printing them out and keeping them in a handy reference file the same as you.

[Dan Walker]

The best glue that I have found to use for something like that is JB weld. It is a two part glue that comes in two tubes.
Let it set[overnight]. It ends up being rock hard.

[Don]

Great. Thanks, Dan. I’ll take a look.

[Don]

Here is what I did for the repair. The suggestion of JB Weld looked good, but I decided to have another go using cyanoacrylate (this time Gorilla Super Glue) and a different approach. When I was talking to the glue guy in the local hardware store, he asked if there was room to cement some kind of reinforcement across the crack. I said no, but then starting thinking about it. I wound up filing/grinding down sections on the disk to make room for reinforcement, glueing strips of plastic (mostly bits I cut from a separating strip from a parts organizer drawer), and then filing/grinding those down so the repaired disk would fit and turn easily inside the volume control housing. Worked great, and once again the old Dynaco amp is pounding bass out through a matched set of Dynaco speakers. Thanks John and Dan for your input. I’ll attach a pic of the repaired shaft, so you can see what I was describing.
Don

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