Repairing Broken Delrin Type Plastic Truck

Good job, but it sure would have been easier to replace the truck frame.

Agree with Chuck that you did a good job with the repair, but if it fails, you can probably find a replacement truck frame for $5 or less.

Also, trucks from that era were made from Celcon by Celanese, not Delrin by Dupont. They're similar acetal plastics from different manufacturers.

TRW

Since the metal in JB Weld doesn't add any adherence wouldn't regular epoxy be better? I have wondered about this.

I don't think JB weld contains any metal at all.

Machining etc. produces no sign of it, not magnetic, does not conduct electricity, etc..   I think it is just a chemically stable, chemically resistant, machinable, hard setting chemical solidification/cohesion.

It will seperate from smooth delrin easily as JBW cure is glossy smooth. However, sanding/scratching give grooves for a pure mechanical bite to take place.  I.e., a thousand tiny dovetail joints once the epoxy sets.   I'm pretty sure that is why Charlie focused on including the info that it was scratched up with a knife; the knife scratches would need a very coarse paper to be equalled.

I find for most epoxy type adhesives that a rough surface is MUCH better for bonding than a smooth surface.  I've stuck JB-Weld to a smooth surface and it came right off.  However, I just roughed it up and tried again, and it was rock solid.

AFAIK, JB-Weld has no metal, and it is not conductive.

I had to repair two Weaver plastic trucks that rolled off the workbench and hit the concrete basement floor, from my past experience most adhesives do not bond plastics such as delrin.  I used a flexible rtv sealant to bond the side frame to the bolster, this repair is holding up, the side thrust of the wheelset in curves is absorbed by the sealant.

  I saw some impact resistant "flexible superglue" at Wamart (loctite brand). Has anyone used it yet. (Really a good topic for a spin off thread too)

  Scratching deep for a mechanical hold is still the way to go for most adhesives, even rtv.  

Hey Charley, that is so cool. Thanks for sharing! This is a trick we may all need to remember from time to time.

Adriatic posted:

I don't think JB weld contains any metal at all.

Machining etc. produces no sign of it, not magnetic, does not conduct electricity, etc..   I think it is just a chemically stable, chemically resistant, machinable, hard setting chemical solidification/cohesion.

It will seperate from smooth delrin easily as JBW cure is glossy smooth. However, sanding/scratching give grooves for a pure mechanical bite to take place.  I.e., a thousand tiny dovetail joints once the epoxy sets.   I'm pretty sure that is why Charlie focused on including the info that it was scratched up with a knife; the knife scratches would need a very coarse paper to be equalled.

JB Weld does contain metal.  Mix some up and put it on a magnet if you are curious.

Which part is the metal?  Here's the MSDS section on what's in it.

I stand corrected, it is (slightly) magnetic.  (thanks)

I happen to have some JBW 1/4" thick around. The strongest magnets stick, weak ones like in plastic alphabet letters fall right off.

   Titanium is mildly magnetic and has very low lenz ability, but it's there I guess.  I had tried using it long ago on wheels, and they stopped conducting to the axle, I got no ohm reading either. I bet you some real good test equipment to read what's going on.  I don't know how to guess on "dioxide", but I'm supposed to see "End Game" with a good chemist and saftey engineer tommorow, hopefully I remember to ask what he knows.

For some contrast, I had unbreakable titanium alloy eyeglass frames I know were not magnetic enough to be be held up by a large electromagnet (junkyard crane)  

Fun: You could bend the metal temples wrapping the length around your finger and they'd spring back into shape. Ball the whole glass frame in your fist and they spring return back to shape.

Like I said, mix it up, put it on a magnet, and see what you think.  It will show you exactly where the flux edge is (or maybe it's just me).

Oh, no question about it; magnets stick to JBWeld.

I don't think it could hold a charge or anything that we could measure, but you sure aren't wrong.

  I started with the weak ones, moved to the strong magnets, then switched from test pieces that had screws and steel frame nearby, as I wasn't totally convinced. But JBW used on Bakelite, with just brass innards, the strong magnets did enough not to fall off under their own weight. They would not lift the bakelight uncoupling/unload button housing.

 If banged or shook even very lighty, they fell off. But that is still being attracted to a magnetic field, no doubt. 

I wonder how a neo magnet would fair? 

gunrunnerjohn posted:

Which part is the metal?  Here's the MSDS section on what's in it.

Nothing ferromagnetic in there, but that also only accounts for a little over 65%; even by weight that's not accounting for 100%.

In any case - very little substantially binds solidly & permanently to most forms of Delrin.  Get a replacement someday before the band-aid repair fails.