Repair of broken hinge on dark glasses

A hinge on one of my pairs of dark glasses got broken.

That’s a big deal. I can’t find dark glasses that I like anymore. I want polarized GLASS lenses (not plastic), with lenses and frames large enough to fit comfortably over my regular spectacles. I want glass because plastic lenses get scratched, or just fog up after a couple of years of exposure to the sun.

Strike King, a company that makes bass fishing lures, used to have such a product years ago. They sold for $49.95 at tackle shops. I wish I’d bought half a dozen pairs because NOBODY makes anything like that anymore and haven’t for a decade now. I’ve had and enjoyed these dark glasses for at least 20 years. I’m not ready to part with them quite yet.

Fortunately, I don’t have to. I have a shop.

Task 1 was to extract part of the metal “stump” of the broken hinge from the bow. That took a bit of futzing around but I finally got it outta there without damaging the bow or scaring my neighbors, not that my neighbors scare easily. That left a square cavity .110” square by about .120” deep in the bow. Oy kin work with that, mate!

I made a brass piece that would fit in that cavity, with the sticking-out part replacing the hinge part that broke.
Attachment 11828

The part was made on a Bridgeport vertical milling machine, starting with a piece of ¼” dia brass rod. It sometimes seems a bit silly making a part that will weigh less than an ounce on a 2000-pound machine – but ya use what ya got. The new part looks a bit rough in the photo but the dimensions are all within .002” of target. I screwed up the first attempt by drilling the hole off-center so I then made an actual drawing (zounds and egad) to take to the mill for the second try. Got it right that time. First try wasn’t an error, it was skill building and process proving; that’s my story and I’m stickin’ to it.

I coated it with epoxy and put some epoxy in the hole, then shoved it in and held it in place with a hemostat for long enough for the epoxy to set. Epoxy is good stuff but I didn’t want to trust this job entirely to glue so I pinned the new hinge part in place. I drilled thru both the bow and the brass insert from the bottom of the bow. That hole was .045” dia because I had some steel welding rod that diameter from which to make a little pin. The hole was 0.220” deep, not quite clear thru the bow. I made the little pin .200” long, pressed it in with a drill press vise, and pushed it the rest of the way home with a bit of wire. It is not visible from the top of the bow. The epoxy made a form-fitted seat for the already close-fitting square peg in the square hole so it can’t wiggle. The pin will ensure that it can’t be pulled out. I then put a drop of superglue in the pin hole to keep moisture from rusting the steel pin.

This hinge has broken before. Last time I had to make the other part of the hinge. This new part fits the old part. The screws are the little screws customarily used in eyeglass hinges. They’re #1-64 screws.
Attachment 11829

Here is the bow with the new part in place.
Attachment 11847

Here’s the final result, ready to go fishing:
Attachment 11848