I learned this technique after building a few Kossel 3D printers and finding slop in the heim joints which then required springs between effector arm pairs to keep the slop out of the 3D print. When assembled this way the joints, once cooled to room temp, are squeaky tight. I posted this in the google delta group in 2016.
Since I’ve not seen it posted anywhere and had to figure this out here is how you assemble the Traxxas joints( metal into plastic ).
Put all the metal parts in a glass container in the freezer for about 15 minutes.
Place cereal box cardboard(single layer/thin cardboard) down on stone countertop for insulation.
Boil a small pot of water with the water level near the top such that you can extract something from the top of the water easily.
You will need 2 pair of tweezers. One for the hot parts and one for the cold parts.
Look at one of the plastic pieces where the metal get inserted and notice there is a shiny recessed ring on one side and a non-shiny/non-recessed side.
Drop one plastic piece in the boiling water and count to 30(seconds) while also pulling out one metal piece which is put on the cardboard standing up on one end(doesn’t matter which).
Place another plastic part into the water and pull out the first one using ‘hot’ tweezers.
Quickly place the hot plastic piece over the cold metal part( shinny ring down ) and using another blank plastic piece to apply force, push the plastic onto the metal.
repeat
Doing this you should get tight Traxxas Heim Joints instead of loose sloppy ones which require springs and rubber bands to keep the slop out. Test them after all parts have reached room temperature.
Traxxas heim joint assembly magic. Still amazing this is not SOP for assembling these it makes such a huge difference in how tight the resulting joints are.