Strengthening a Plastic Item: Binocular Tripod Adapter




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.



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    5 Discussions


    Reply 7 years ago on Introduction

    That's a neat idea, but I suspect it would still have some wobble. Here I needed something solid since each movement gets magnified quite a lot.


    7 years ago on Introduction

    Two updates:

    1. I read a hint that if you run a hair dryer on the JB Weld when you put it in, it will flow much better, and will self-level. That wouldn't be great for this project, since I don't want an exactly level edge--I want a bit of a curve to it--but might be useful for filling in some other items.

    2. My JB Weld on the second was setting very slowly and it seemed like there was some separation of the ingredients. After over 24 hours, I ran a hairdryer over it a fair amount, and that helped. I think my shop-size pack needs to be replaced by a fresh pack--I think I've had it for two years.

    would it add any strength to the object if you could cut the steel rod to fit securely and forming a shape such as you see bridge builders use. Like forming a triangle or some other truss within the piece, would that make it any stronger?
    Not so much in this particular piece but if you had a rectangular or box-shaped.

    1 reply

    I bet a truss would be nice.

    But JB Weld in the kinds of quantities that this item got in it is going to be plenty strong enough. Adding the metal was as much about saving on JB Weld--my trusty shop-size pack is running out--as on adding strength.