I was sitting on the sofa reading and my right lens suddenly dropped onto my lap without warning. The monofilament (fishing) line broke from several years of normal wear. I was very thankful this did not happen while I was doing quite a number of other things I normally do, like riding my bike on a country road.
It was the weekend and my optometrist's office was closed. I am a pastor and had to lead the worship service on Sunday without my glasses. There is a lot of reading involved. I got by with a pair of reading glasses, but everything more than fifteen feet away was a big blur.
I searched the Internet for eyeglass repair. There was nothing about replacing a broken monofilament lens retainer.
Step 1: Anatomy of an Eyeglass Frame
The parts of an eyeglass frame where the monofilament line attaches to hold the lens are very small. The colors of the frame and of the line blend into one another much more than shown in this drawing, especially when you are looking at them without your regular glasses.
The left portion of the drawing shows the end of the frame if the glasses are upside down on a countertop as in my first photo and you are viewing the frame from the side where the bows attach. There are two small holes near the end of the frame. The monofilament line loops through these holes. The 90 degree bends the line must make keep the line from slipping when the lenses are in place. The graphic in the next step will give you a clearer picture of how that works.
The right portion of the drawing shows a cross section of the metal in the frame and the channel on the inside of the frame where it contacts the lens and supports it. The gray circle is a cross section of some monofilament line permanently embedded in the frame. There is a corresponding groove around the circumference of the lens and that groove fits over the embedded monofilament line to keep your lens in place where the frame goes around the lens.
Step 2: The Line's Pathway
The drawing shows the pathway the line makes through the holes at the ends of the frame. The left portion of the drawing shows the line (gray) and the frame (brown) as viewed from the side of the glasses near where the bows attach to the frame. The right portion of the drawing is a side view and shows the bends the line must make. The lens would fit against the left side of the view in the right portion of the drawing. The stubby end of the line is supposed to press down into the channel so it does not interfere with the fit between the lens and the frame.
See my Instructable titled "What gage is that steel or wire?" to determine the thickness of the monofilament line your glasses use. Or, try to match up the end of a spool of line when you are in the sporting goods department of your local store. It appeared 0.029 thick 50 pound test line should have worked, but it would not thread through my holes without a lot of work forcing it. I chose 0.022 thick 30 pound test line. A spool of 400 yards was about six dollars US.
Use a knife point to pry the old broken line out of the frame holes. Attach the end of the new line as shown at the end of the frame near the nose pads. Place the lens into the frame and pull the line over the circumference of the lens. Cut the line so it is an inch or two longer than needed.
Remove the lens and thread the end of the line through the frame holes near where the bow attaches. Before trimming excess line, place the lens in the frame and pull the line over the lens. This will show you how much you need to cinch up the line so it will be tight when the lens is permanently mounted. Remove the lens and adjust the length of the line between the ends of the frame. Keep working at this until the lens will be held firmly by the line.
Trim the line to length and try to press the stubby end into the channel. I was not able to get it to go into the channel, not even with a needle nose plier. My lens seems to stay firmly in place, anyway.
Step 3: Mounting the Lens
In the photo the monofilament line is represented by the red line I drew in a photo editing program. This photo shows the way to proceed in order to secure the lens in the frame with the line. Pull the line up over one corner of the lens and hold it there with your fingers.
Step 4: Mounting the Lens--step 2
Move your fingers along the lens pulling the monofilament line over the lens and into the groove for the line. Finally, roll the line over the other corner of the lens.
My frame does not fit around the lens quite as tightly as when the glasses were new from the factory. But, the lens does not wiggle and it seems to work very well. I wish I had thought of all of this on Saturday evening when my lens fell onto my lap. I could have gone to the sporting goods section at our 24 hour big box store and had my glasses working for me again after about 30 minutes of work.
I have not checked yet with my optometrist to see about an official repair of my monofilament line. My wife talked with someone at church Sunday who had experienced the same problem. She had to send her glasses away for several days to get a new monofilament line installed. One listing in the search engine when I was looking for information on replacing the monofilament line appeared to advertise various repairs to eyeglasses. It appeared that business was charging $25 US for replacement of a monofilament line. Who knows? Maybe my optometrist would do it for free while I wait. But, he will not be open for a while yet, and I am using my newly repaired glasses as I am preparing this Instructable.