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Minidisc repair - best glue for bonding nylon gear to metal shaft?
Minidisc repair - best glue for bonding nylon gear to metal shaft?
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Old 7th November 2017, 05:48 AM   #1
ChopperCharles is offline ChopperCharles  United States
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Default Minidisc repair - best glue for bonding nylon gear to metal shaft?

I'm repairing the minidisc unit out of a Kenwood MDX-G7. Super rare portable combo unit that has minidisc, AM/FM radio (Japanese FM band), and CD player, with fold-away speakers and a carry handle. It's a really slick unit. I paid not a whole lot for it off of eBay, because the MD drive doesn't work. The unit has a little mark on the case, right on the MD drive cover, where it looks like it was dropped.

So, after about 13.7 quintillion tiny little screws, I got to the heart of the problem. There is a nylon gear that is supposed to be attached the the worm gear that moves the laser back and forth. The nylon gear spins freely on the shaft. I have the gear end of the shaft free and can easily remove the nylon gear, without disturbing the rest of the assembly. The question now is... what do I use to bond the gear to the metal shaft? Superglue?

Note, I would have expected this gear to be a press-fit onto the shaft, like so many crappy tape decks of ages past... but it's too loose on the shaft, and the gear is not cracked in any way. Usually a cracked nylon gear that was press-fit onto a shaft still retains some drag on the shaft. Not so in this case, it spins very freely on the shaft, which it should be attached to. I think it was originally held in place with an adhesive, and the shock broke it free. That said, there's no evidence of adhesive on the shaft, so I'm not 100% how it was bonded. Yet bonded it was.

So.... superglue? That going to work? (Of course ZAP or Loctite brand)

Thanks!

Charles.
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Old 7th November 2017, 07:06 AM   #2
Mooly is offline Mooly  United Kingdom
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Minidisc repair - best glue for bonding nylon gear to metal shaft?
Superglue can be pretty good with some types of nylon and useless on others.

Only you can make the judgement call but one possibility is to 'touch' a hot soldering iron tip on the inside of the gear, just enough to distort the surface and give it some friction, and use a dab of epoxy on the shaft to secure. Heating the shaft a little (soldering iron again) would allow the epoxy to flow.
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Old 7th November 2017, 08:07 AM   #3
japtim is offline japtim  United Kingdom
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Glue sounds a bit hit or miss
Any chance of drilling a small hole and popping a tiny roll pin in ... you know it's there to stay then...
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Old 7th November 2017, 09:31 AM   #4
T129 is offline T129
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Look for Loctite 438. If the fitting is tight, sliding the part will be a bit difficult as it grabs little too fast. 480 gives similar properties but a bit slower curing time. The bonding of greasy polymers is a problem, but thorough cleaning and especially baking the part will help a little. Check this for help: Bonding Nylon | Industrial Adhesives | Polyamide Surface Preparation

If one wants to be really serious about it: bake the gear, carefully knurl the axle (side of a file is enough) and use a methyl methacrylate adhesive (Loctite HHD 8900 for example, I have no idea where to get this in consumer quantities though). I must point out that any glue applied will have an effect on the lifetime of the part. If you are very unlucky the formulation of the gear polymer is such that it will crack during the gluing or immediately during testing. But in general, I doubt that or even significant deterioration of properties will happen.

Edit: Oh, and be absolute sure the curing has finished before assembly. I would wait minimum 24 hours. You don't want the fumes ruining the laser lenses.

Last edited by T129; 7th November 2017 at 09:41 AM.
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Old 7th November 2017, 10:00 AM   #5
Extreme_Boky is offline Extreme_Boky
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Selleys Araldite Super Strength - Epoxy Adhesive | Selleys Australia
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