Locktite and plastic

[Anonymous]

The short question is whether anyone has attempted to use Locktite with plastic?

I wanted to add ART wheels with power pickups to a Hartland working caboose.  I chose not to use the Hartland trucks because the ART axles are longer than the Hartland ones.  The ART wheels fit Bachmann trucks so I used Bachmann trucks but because the wheels were to close to the undercarriage I had to shim them with a washer.  Because this reduced the length of the screw in the plastic post, I used some Locktite to avoid the screw coming lose.

After a few hours of running, both trucks fell off - the plastic posts broke.  To remove the screw from the broken off part of the post I had to grip the section of post with some pliers - gently.  The short section of post crumbled when attempting to get the screw out.

Worth noting is I also lubed where the post goes through the hole in the truck - although I used lube that is supposed to be OK with plastic.

On a related note, what techniques do folks use where screws aren't holding in plastic?  The best I've come up with is putting a piece of small diameter solder in the hole where the hole is too small to accommodate the old trick of using a broken off piece of toothpick.   

Bob 

 

 

 

 

[Capt Bob Johnson]

I've never heard of using loctite on plastic, and from your description it looks like it eats plastic.  When screw threads in plastic were stripped on equipment bought used, I've put a drop of super glue in the hole before the screw and let it set up overnight!

[GearDrivenSteam]

Locktite makes a bunch of products for plastic.

http://www.loctiteproducts.com/glue.asp#results

[Mr_Ash]

I use superglue (Not Gel!) on stripped screw holes

 

[tangerine-jack]

I don't normaly use loc-tite on plastic, but as was pointed out they do make compatable products.  For stripped threads I drill oversize and use the next larger screw wherever possible.  If not, then a small bit of epoxy works great- but be sure to coat the screw with some non-stick cooking spray or it will never come out again when you need it to.

[JD Miller]

Bob,

It's too bad you found out the hard way what has been generally known. Loctite will attack plastic. Sometimes the damage is immediate, or it may take an hour or so. 

Now you will have to come up with king posts. On way on the Hartland is to drill down through the floor with the hole centered where the king post use to be.  Install a machine thread bolt (probably #4), of appropriate diameter, down through the hole and fix it in place with 5 minute epoxy.

The mounting hole in the Bachmann truck will be too large for the bolt. Make a bushing to take up the excess space. Fit the bushing in the truck bolster and install the truck on the bolt. Use the bolt nut and a flat washer to attach the truck.

Down side is the head of the bolt securing the front truck will be exposed. Maybe you can come up with some detail item to cover/hide the head.  There are other methods to make a king post, this is just one that has worked for me.

The suggestion to use epoxy to repair damaged threads is a good one. As mentioned, make certain the screw is coated with something like cooking oil or a very light grease so the epoxy will not adhere to the screw.  This is an easy repair and as indicated, it works.

[Anonymous]

Thanks JD.  Usually I'm careful about checking on products before I use them but I was in a rush - oh well.

I may have enough of the post left to hold a screw in which case I'm going to machine something that would look like a T-nut - giving me a post and the "washer" needed to get the wheel clearance for Bachmann trucks.  If not, I'll go with what you suggest although a bushing will be a strange size.  I'm measuring about .270 for the Bachmann truck hole and around .265 for the post - neither which convert to either common inches or metric sizes - my measurements must be off. 

Interestingly, I recently had a similar problem with one of my made in China RC planes.  A rod that slips into a sleeve didn't measure a standard size of either inches or metric.  It's like they set their machining up for what works even though it isn't a standard measurement.  Strange.  I don't doubt my calipers because they're on the money for known things I measure.  The good news is I have access to a lathe.

Bob 

     

 

 

 

[Anonymous]

Interestingly, I recently had a similar problem with one of my made in China RC planes.  A rod that slips into a sleeve didn't measure a standard size of either inches or metric.  It's like they set their machining up for what works even though it isn't a standard measurement.  Strange.  I don't doubt my calipers because they're on the money for known things I measure.  The good news is I have access to a lathe.

Bob

Hmmm is there a standard any more? Think people just use it as a word now! I feel your pain

[selector]

Hi.  I am over in the model railroaders forums usually, but happened across the title of this thread.

What guys in my scale do is to drill out the bad spot with a known drill bit size, one that matches the outer diameter of a solid dowel of styrene plastic.  They cut the dowel to a suitable length and glue it into the drilled out hole cementing it with a range of suitable glues...MEK, CA, Gorilla Glue (easy does it), and even lacquer thinner will do.

Leave it.  Two or five days later, drill out and tap to suit.  Yer back in business.

[Anonymous]

Thanks, that sounds like a tidy solution.