For plastic i use Revel glue in the needle point bottle, does a realy good melt bond on plastruct products
For metal-metal, metal-plastic i use JB weld, 2 part epoxy resin steel, wonderfull stuf, i have both versions 15hr cure, and Quick, 4min cure, best thing is you can file, sand, work , drill this stuff after 1 hr, can take weight in 4 min
i use Arildite 90second for any thing that doesnt take alot of weight, Jb weld quick has replaced this realy