Fix broken plastic pieces with plastic welding
Here's how I fixed some license plate light covers using some quick and dirty plastic welding. These covers are from a 2001 Toyota Tacoma and had cracked around the screw holes.
To see what we're aiming for, here are some before/after/original shots:
It's not pretty, but these pieces aren't visible - they just need to function properly.
To begin, I cut off a piece of scrap plastic from an old stereo mounting bracket.
I marked the filler piece to get a rough outline of the shape I needed.
Then I cut off and sanded down the extra material.
The filler piece doesn't have to be a perfect match - you just need it close enough that you can melt it into shape.
After the scrap piece was shaped, I melting together the two pieces pushing down and forward with the wood burning tip. The melting plastic gives off nasty fumes, so a respirator during this step is a must. I use this 3M Comfort quick latch respirator with these 3m cartridges.
If you have any gaps you can fill them by melting in some plastic shavings.
After finishing the front, I flipped it over and melted together the back. At this point I had completely covered over the screw hole, but I just re-drilled that later.
Once the repair piece was fully molded into place, I sanded it down to shape. You can see here the replacement piece is super secure, even while being hit with the high-speed Dremel.
Here's some shots of the finish pieces all repaired and ready for re-assembly.
Fixing plastic this way isn't necessarily pretty, but it's stronger than glue and you don't have to wait for the repair to dry before working with it.