FIX AND FIT

Rimless eyewear styles are more popular than ever. But that very design brings with it unique challenges when it comes to fitting the eyewear, edging and mounting the lenses, and fixing the frames.

What can I do to prevent rimless lenses from loosening or breaking?

Here are a few general tips:

First, it's not healthy for a drilled rimless mounting to be too tight. Usually you can see a slight pressure distortion very near the lens screws. A great deal of distortion means a great deal of pressure and an increased potential for breakage. It is important that the holes and slots are exactly the right distance apart. Many labs have abandoned hand drilling for the new computer aided drilling and slotting machines. These not only reduce the tightness needed for a poorly drilled mount, but also eliminate problems caused when lenses are not exactly bookmatched.

Any sharp edges on the lens should be smoothed, especially where there is pressure. This can mean not only the "pin" bevel, but also chamfering the edges of holes and notches. If you have a hole with a rough edge, it can be easily smoothed with a round diamond burr that is at least twice the diameter of the hole. Slot edges can be knocked off with a diamond rat-tail file.

The screw assemblies that mount the lenses are also critical. A lens should be protected on both sides by a "top hat" washer, which is a plastic bushing that resides partly in the hole of the lens and partly on the face of the lens. If the rimless mounting has only one strap to anchor the screw, it is important to put a flat metal washer after the top hat bushing on the opposite side of the strap. This will keep the nut from crushing the bushing and possibly gouging the lens.

The single strap mountings have a disadvantage when compared to the frames that have a strap on both sides. The single strap type do not survive bumps very well. As the frame gets bumped, the strap angle is opened up, allowing the lens to pull away from its stabilizing embuttment. You will know this has happened because the lens will rotate on the screw. The only way to safely correct this is to remove the lens, and bend the strap back to the "L" shape it had originally.  EB