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Loctite and ABS = Gallium and Aluminum...



So over the past few months, I've been trying to find ways of making the RCA jacks that I install into consoles more secure so they don't free spin over time. What I've been doing in the past that actually works 90% of the time far as I know...is that instead of using the small lock ring washer that typically comes with RCA jacks, I use inner star washers of the right diameter to do the same thing, but with more points of contact to lock into the plastic. It also has the advantage of holding the securing nut in place tighter as well since the inner teeth of the washers are present on both sides of the washer. From there, I've used light amounts of epoxy to help hold the securing nuts fast in place as well. 

This has worked well for years but recently I did have some consoles start to come back where one or more of the RCAs had still somehow managed to work loose over time. So this got me to wondering if there were other methods I could employ. 

Enter the idea to use Loctite or something similar... Hang tight...there is some history I have to talk about first and a lot of details to follow. Grab a snack and drink and settle in...

Now there are two types of loctite that you can get for threading applications. One is the red colored stuff and is essentially permanent in that it is very very difficult to remove nuts off their threads if that stuff is used. The other is the blue kind that still allows the parts to be separated (Although not nearly as easily as without...). So I decided to try the blue stuff.

Now I will say that sure enough the blue loctite holds really well. It basically is a liquid that once exposed to air begins to congeal and turn into a rubber like substance. As a result, it acts as filler between the threads of the nut and the jacks you are securing together. It does still come undone but requires a lot more force to do so and actually squeaks while you remove the parts after it has cured. So it does its job... but... there is also a warning on the package that I did read but didn't think would be an issue in this case.

The warning says not to use with plastic threaded parts. So I assume this meant not to use it with plastic bolt/nuts sets commonly made of Teflon and the like. Well... I'm here to tell you that isn't the only issue.

Over a month ago, I installed a UAV into an 800xl. The owner requested I install a separate standard 4pin s-video jack in the opening that the RF modulator used to occupy as the opening is nearly the exact size needed for one style of s-video jacks I have on hand. But they also wanted a pair of RCAs for audio to be installed. They didn't want to purchase an Atari monitor cable specific for this hence the request for separate jacks. So I drilled in the needed holes and got the jacks line up great! To install them, I used a bit of the loctite on the threads of the RCA jacks and proceeded to tighten everything up as normal. I then set the case shell down for about an hour while I recapped the main board and did other things. When I picked up the bottom shell housing I was horrified to see that a long crack had formed between the two RCAs that ran beyond top to bottom of the shell?! I removed the RCAs and discovered that around the holes where the jacks had been installed, there were small spider cracks around the openings and the plastic appeared to be much more brittle than I remembered? So I cleaned everything up and applied some epoxy across the cracks on the inside of the case shell to restrengthen the area and prevent any further cracks from occuring. I let it cure for about 2 days before reinstalling the RCA jacks. This time as they already had the loctite on them, I didn't apply anymore and just had to crank down a bit more to tighten them back up. This time I left them a little more loose than normal and then applied more expoxy over everything to make sure it all held tight. And this worked fine as expected.

My thinking at that time was that I had simply tightened the nuts on the RCA jacks too much and it caused stress fracturing in the plastic that spread out. Didn't think much of it beyond that.

Last night while working on a 5200 (A console I've done this work on a LOT of times), I drilled in the holes on the expansion plate as normal using a template I've had for years now. Installed the RCAs and again used some loctite on the threads to secure them nicely in place and then set it aside for about 30min while doing other things. I picked it back up to solder the wiring to it and again was horrified to see a crack had formed vertically between two of the RCA jacks?! I was like, what the heck?! I've done a lot of these 5200s and the expansion plate has never done this before? When I started to remove the RCAs to inspect, the entire thing just started to crumble in my hands like dirt. Sure enough the entire plate had become super brittle and was falling apart in my hands?! At this point I was pretty sure I knew what was happening and decided to test on another piece of similar plastic. Scratched it to expose the inner plastic and applied a little loctite. Yeap... that little piece of plastic became a brittle mess within about 15min of application.

So.. the lesson here is that Loctite chemically reacts with ABS plastics and causes the ABS to breakdown at a molecular level in a very similar fashion to that of gallium when put in contact with scratched aluminum. Going forward, I'm just going to have to stick with my star lock washers and epoxy it seems...



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3 hours ago, RickR said:

Who knew? 

Thanks for sharing.  I would have probably tried Loctite myself, so thanks for the warning.

I've been told this is likely just an issue for ABS plastics that of course all of our stuff was made back then. Apparently PLA used with 3D printing isn't affected as much? But I don't have the means to test that myself. But yeah... kinda disappointed too since I had really thought this was the fix I'd been looking for to keep the AV jacks I install nice and tight, but ehh. It isn't.



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