Some flimsy plastic items aren't flimsy because they have plastic in them, but because they don't have enough plastic. Case in point: the tripod adapter for the Celestron SkyMaster 15x70 binoculars. The binoculars weigh three pounds, and magnify any wobble 15X. But the adapter for them is a piece of plastic mostly hollow, and hence too wobbly.
A standard solution from the Internet is to fill the adapter with epoxy, and that's what I did. But I did one better. I also sunk some scrap metal into the epoxy: some screws from my scrap screw collection as well as leftover bits of a 3/8" steel rod. This increased the solidity of the result while decreasing the amount of epoxy that would need to be used, and hence decreasing the cost.
The epoxy I used was JB Weld, which is nice and heavy. I recommend a slow-curing epoxy, not the five-minute kind, so you don't have to work quickly.
The first photo shows the strengthened adapter. The second shows the "before".
Step 1: Find Bits of Metal and Mix the Epoxy
First, find scrap metal that can fit into the hollows of the plastic object.
Then, mix up the epoxy for one side of the object (if the object has more than one side). Try to keep the proportions as per directions--1:1 in the case of JB Weld--and make sure that everything is thoroughly mixed. In the case of an epoxy where the two parts are different colors, like JB Weld, this is very easy to tell. Keep things well ventilated. I like to mix up epoxy on a paper plate.
Step 2: Put in the Metal and Epoxy
Cover up anything you don't want to get epoxy on with painter's tape. First, put down a bit of epoxy. Then insert your scrap metal. Then fill in the hollow areas with the epoxy. (I also did some hollows on the underside.)
Pop any bubbles and smooth a little. If the epoxy is slow curing, you don't need to smooth it very much--gravity will do it for you. Wipe off any excess epoxy.
Step 3: Leave to Cure, and Repeat
Now leave the epoxy to cure, but make sure that the object lies in such an angle (I used the crumpled up paper towel to do that) so that the epoxy doesn't pour out of it--keep it horizontal. The epoxy may be thick, but if it's slow setting, it's going to flow for a couple of hours.
You may want to monitor from time to time to make sure things aren't lopsided.
Step 4: Repeat If Necessary
Once one side is done, repeat for the other as needed.
The photo shows the first side. The second side is curing more slowly--I think I didn't get the proportions quite right. JB Weld turns duller in color once it's cured. The photo shows the side that's done.
The resulting adapter should be much, much more stable. (I haven't tried this one yet, but I have used another one I did earlier.) It also has an impressive "expensive-feeling" heft, since it now weighs in at 4.5 oz.