Maybe this has been posted before, but I was unaware of this.

I have been assembling my quadcopter and as advised have used red loctite # 271 to lock the metal nuts and the prop mounts.

I have used it all up and bought some blue loctite #243 and have used it on some of the nylon nuts last night and have just noticed today that it has eaten away the part of the nylon bolt inside the nut and the nylon nuts are soft and easily split in two with my thumb nail.

I must hold my hands up and admit that I didn't realise that threadlock could do this to plastic, but thought I would bring it to everybodys attention.

Martinp

 

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3D Robotics
Comment by Chris Anderson on October 28, 2011 at 3:08pm

Thanks for the warning! (Why is it called "Blue"?). 

 

I used Locktite green, which is supposed to be used once the nut is already in place. Is that okay with plastics?

Comment by Ellison Chan on October 28, 2011 at 3:23pm

Why put Locktite on nylon nuts?  Nylon is already the locking mechanism.  There's no vibration that'll loosen the nut.  I would think that any kind of locktite would dissolve plastics, since it probably contains solvent to liquify the polymer that does the locking when dried.

Comment by Jeff Taylor on October 28, 2011 at 4:08pm

The loctite is really only needed in two places - on the screws connecting the legs and arms and on the screws connecting the arms and the main frame. I wouldn't worry about vibrations on the stackup portion. As Ellison pointed out the Nylon does a great job of staying fastened as they are.

Comment by Ryan on October 28, 2011 at 4:45pm

If you use locknut then don't use Loctite!

Comment by Jesse on October 28, 2011 at 5:37pm

Locktite is only for metal-to-metal contact.

 

"Blue" locktite is a "general purpose" locktite and it's colored blue.

"Red" locktite is stronger and typically requires a heat source to undue. It's colored red.

Comment by Martin Szymanski on October 28, 2011 at 5:53pm

Locktight reacts with metal interference and catalyz'es faster.

As well as heat, acetone or fingernail polish remover will remove a locktight connection.


Moderator
Comment by Brian on October 28, 2011 at 8:56pm

Blue helps to keep my motors attached to their mounts.  Blue can be loosened, Red is considered a permanent lock, Purple is very easily loosened.  

Comment by Justin Stiltner on October 28, 2011 at 9:16pm

The locktite does not dissolve the plastic, but will cause it to become extremely brittle and crack easily.  This does not happen with all plastics however, I have a feeling polyethylene would be ok with it.  In RC Helicopters the rule is that locktite is used for metal to metal, and CA (superglue) is used for metal to plastic connections.  I always use one or the other when assembling any model, and clean the threads first with alcohol to remove any oil before assembly.

 


Moderator
Comment by Sgt Ric on October 29, 2011 at 1:21am
Right...I once had a Graupner Bell helicopter that had a glassfilled nylon frame that I used Locktite on all thehundreds of small screws and the next day I had hundreds of small cracks at the site of each screw.
Major fail.
Now I only use it for metal to metal!
Comment by Martin Poller on October 29, 2011 at 4:17am

Thanks all, as I said I was unaware that it could attack plastic in that way.

@Chris, the various grades of locktite come in different colours, red, blue and green I believe, you're supposed to select the correct grade according to components that you are locking and what their duty is.

@Ellison, I was simply taking on board the general advice of the forum that vibration is a problem and nuts can undo themselves.

@Jesse, you're correct I had to use the cooker to release two of the spinners (after I had removed the spinners from the motor shafts)

@Sgt Ric, I'll follow your advice in the future and only use it in metal to metal from, and I'll use blue or green and avoid red I think.

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