The cracking of white plastic in cheapish tape transports... - diyAudio
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Old 29th April 2010, 12:27 AM   #1
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Default The cracking of white plastic in cheapish tape transports...

Hi All

Most 80's onward, cheapish Japanese tape transports (video recorders particularly) all have some pulleys, idlers and levers made out of a smooth white plastic that becomes brittle and cracks. Often this is where a pulley has been press-fitted onto a steel shaft - it splits and no longer grips the shaft.

What is this plastic and is there any solvent for it (to do solvent welding).
All the organic solvents I've tried have no effect on it at all. And no glue bonds to it with any useful strength.
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Old 29th April 2010, 02:00 AM   #2
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It's normally nylon - try silicone, or even a hot glue gun (more for the heat than the glue).
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Old 29th April 2010, 02:54 AM   #3
m12ax7 is offline m12ax7  United States
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Cheap white plastic...

As already suggested it's probably nylon. I've not seen nor had much luck welding/gluing nylon. Once it becomes brittle it's like trying to chase rust on a car fender.

There are a few other types of "white smooth" plastics UHMW and Acetal. They too can become brittle and crack.

That same crappy plastic is showing up to often.
I've a 2001 Jeep, and it's window regulators fail on a 'regular" schedule, most often because the CHEAP white plastic pulleys or the Cheap white plastic guide the steel cables attach to break.

Not sure what it is you are trying to fix, a pulley.. lever guide or what ever.. it may be better to manufacture you're own part.

I've seen examples of plastic mounted to stamped metal frame and when it "breaks" it's broke.

Good luck!
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Old 29th April 2010, 01:15 PM   #4
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Originally Posted by m12ax7 View Post
Not sure what it is you are trying to fix, a pulley.. lever guide or what ever.. it may be better to manufacture you're own part.
This time it's the clutch from a friends portable cassette boombox (Sony on the outside, but inside the nastiest piece of OEM stamped shim plate & plastic I've ever seen). Fortunately in my box of collected spare parts I had a pulley that fitted. But next time....?

Occasionaly I have had success forcing a few turns cut off a coil spring over a pulley - IF it is wide enough and has extra 'space'.

Something DIY filed from brass or aluminium is sometime possible - agreed.

It would be so convenient if there was a good solvent glue for this plastic!
Computer says trifluoroethanol is a solvent for nylon, and hexafluoroacetone sesquihydrate for Acetal Copolymer - I'll try buy some & see.
Toluene possibly dissolves UHMW PE they say. A bottle of each of those could be useful to have anyway!
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