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Threadlocker damage to plastic. The gift that keeps on giving!

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I never knew how badly the stuff could effect plastic till a few years ago when some leaked from the motor screws of my heavy dump truck and also from a couple of bearings I had locked in place to prevent from spinning on the shafts.

The damage wasn't exactly extensive but there were plenty of little hairine cracks through the plastic where the motor mounts and a tell tell blue stain here and there.

After discovering it, I totally stripped and cleaned the chassis and the damage seemed to be isolated to just a few places. 

57GmS2Y.jpg

You can see some of the staining more clearly in this crop:
image.png.20a9b39a7886b40458921241e7ab7d7e.png

The crazy thing is, in the couple of years since this happened, I've continued to notice fractures occurring in the chassis. In fairness, I haven't exactly been gentle with it and it's mostly happened along the underside of the chassis where it takes the brunt of heavy landings etc but the nature of the damage in unmistakable, hairline cracks and fractures accompanied by a tell tell blue discolouration. 

OkZwwos.jpg

This screw doesn't go into metal and has never had threadlock on it but the nature of the cracking is atypical of the brittleness caused by threadlock.

I2Sza6g.jpg

Even some of the areas where the two halves of the chassis join together appear to have that slight blue tint.

LuukNh2.jpg

I suppose this could in theory be caused by the small bead of grease I put around the lip where the halves meet but I doubt it as A: Super lube is famously plastic safe, B: It's white coloured grease, not a hint of blue it in and C: Other parts of the chassis, especially the upper facing halves, have no such discolouration despite having the same grease on them.

8WhoWaI.jpg

There wasn't really any particular point to this post other than to share my observations. The yellow plastic makes it easier to spot, too. I'm just amazed at how much damage just a little bit of spillage can cause and how the effects are long term, even after you think you've washed off all traces. Seems like it's too late by the time it has penetrated the plastic. Although it looks bad, the chassis still seems to be holding together pretty well and I have a spare one on hand but still, it's kind of scary how it seems to have such long lasting effects.

Everyone knows to avoid using threadlock to secure screws into plastic but I advise great caution even when securing metal to metal if there's plastic sandwiched in between or close by. Better to use CA based alternatives when possible or get some threadlocker in stick format as it doesn't tend to wick like the liquid stuff can. If you have to use the liquid stuff, make sure to use just the tiniest of dabs and mop up any excess. Just a fine film of it on the screw threads is enough!

And if you want to stop bearings spinning on shafts, use clear nail varnish! The advantage is you can use it on the outside of the bearing where it sits in the plastic, too. That way you can be really sure it isn't spinning on the shaft or in it's seat.

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Thank you for posting. 

Until several years ago, I did not know that threadlocker would damage plastic.  I imagine many people will benefit from knowing this. 

 

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3 hours ago, Juggular said:

Thank you for posting. 

Until several years ago, I did not know that threadlocker would damage plastic.  I imagine many people will benefit from knowing this. 

 

I never knew before I started reading it on RC forums. Luckily I never tried it on any plastics before I found out the hard way. 

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When I've used it on the xv01 I've put the thread lock in the female part then wound the screw into it and removed the excess. Hopefully that will minimise the contact with the plastic and also the fumes/gases given off contacting the plastics.

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I should probably clarify that I didn't apply it to any of the plastic. Only to the motor screws and between the bearings and metal shafts. But it apparently wicked it's way onto the plastic from those locations. the motor aspect is particularly worrying as many people threadlock those screws to stop the motor coming loose. I applied it very sparingly, too, and it still managed to spread quite far.

FRTotgW.jpg
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There's some situations where you inherently have to bring the part with threadlock into close proximity with plastic.

I wonder if I have other chassis with the same issue and just haven't noticed due to them being black. All I know is, I've never used threadlock on a motor since then.

That's why I would advise a tiny dab of CA glue instead or at least stick type threadlock. It's a shame they don't just put nyloc inserts in the motor mounting holes!

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I would imagine motor screws wouldn't come loose if the motor mount is plastic, since the inherent flexibility of the plastic acts like a thrust washer of sorts. If the motor mount is metal, then threadlock is probably adviseable, and not harmful to the metal motor mount anyway.

But I'm not sure what to do with assemblies that require threadlock while at the same time going through plastic to reach the other metal piece. A good example of this is the removable spur gear that is held onto the aluminum spur holder using 4 short screws, typically 5 or 6mm in length. You can't tighten the screws all the way because they'd warp the spur gear, so you HAVE to use threadlock, pass them through the plastic spur, and screw them into the spur holder. Threadlock is bound to touch the spur gear unless you have perfect finger dexterity, which I most certainly do not. You can find this on the (upgraded) XV01, the FF03/04 Evo, and I imagine quite a few of the TRF touring cars.

Just bad design?

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Could you...

- put the threadlock on the end of the screw then wipe it off with a cloth so that it's only occupying the root of the thread, therefore less likely to contact the plastic?

- put the threadlock in the hole and not on the screw?

- put the screw in then put threadlock on the end from the back of the hole (if you can reach it)

- use something other than threadlock that won't damage the plastic, like cyanoacrylate?

- use a longer screw and tighten a nut to the part extending beyond the hole?

Edited by rich_f
Added another idea

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I've used candle wax instead of threadlock (not on my RC cars - on other things).

My dad taught me that one...

Terry

 

 

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I only use thread lock when screwing into metal parts, for plastic I fill the hole with epoxy resin and then retap. Never had issues doing this - but it's a bit of a faff!

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I use a thread locker stick where needed on metals only.. it's in a chapstick like container.  Quite convenient as it does not run like regular thread lock.  I've yet to see if it has any long term side effect where very very tiny amounts of excess got on the plastic.   

I love the smell off Tamiya's thread lock.. maybe TMI.. :lol:

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2 hours ago, DeadMeat666 said:

Just bad design?

2 hours ago, DeadMeat666 said:

I would imagine motor screws wouldn't come loose if the motor mount is plastic

 

Hotshot style too. Where the screws go through the plastic arms into the metal ball plates. I had a Boomerang that kept shedding those screws so of course I looked, it up and people said use threadlock. Bad idea!

In my case, I just had one vehicle (plastic mount) that kept doing it, looked it up online and saw people saying stuff like "ALWAYS USE THREADLOCK!" And so, for a time, I always used it. 

 

1 hour ago, rich_f said:

Could you...

- put the threadlock on the end of the screw then wipe it off with a cloth so that it's only occupying the root of the thread, therefore less likely to contact the plastic?

- put the threadlock in the hole and not on the screw?

- put the screw in then put threadlock on the end from the back of the hole (if you can reach it)

Tried all sorts of ways to mitigate it but it always seems to wick it's way out again. It's amazing how much a tiny amount can spread.

1 hour ago, rich_f said:

- use something other than threadlock that won't damage the plastic, like cyanoacrylate?

That's what I tend to use now, just a tiny dab of cyanoacrylate type glue. Never had a problem. Clear nail varnish is fine too. I like to use nail varnish when there's slight play between the inner and outer races of bearings and their respective parts too. Stops bearings from slipping on shafts and also slipping inside their seats such as those moulded into gears or knuckles etc. Picked that one up from helicopter people. A bearing slipping on a shaft in one of those quickly results in a nicely "machined" notch in the shaft.

99% of motor screws stay put anyway. I think I just happened to have an exception and it lead me down a dodgy path. I'm pretty sure in my case, it was more to do with acquiring an old 80s rc where the motor screws had been in and out more times than a......and as a consequence, weren't holding in place very well.

 

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