Every category of eyewear processing has its own challenges. For sunwear, the issues of edging and tinting are the biggest dilemmas for labs. It can be tough to make the lenses cut out properly for those fashionable wrap-around sunglasses. Without guidance, edging coated lenses is another tricky proposition. Likewise, the tinting process raises its own questions. Fortunately, the experts have the answers. Here, they share them with the rest of us.

Rx In Wrap-Arounds

Problem: Some of our patients want us to put prescription lenses into wrap-around sunglass styles. We haven't been able to make the lenses fit into the frames without falling out.

Solution: It's best to order a high-base-curve lens from the lab when you're putting prescription sun lenses into a wrap-around, or high-base-curve frame. The average frame has about a 5 base curve, but wrap-around frames have about an 8 base curve. The average Rx lens has a base curve of about 5 to 6. The lab can grind an Rx on up to a 7.75 base curve.

If you try to put a stock lens into an off-the-rack wrap-around sunglass, it won't stay in the frame because the frame has more curve than the lenses. You can't change the shape of the lens, but you can order a lens with a more suitable curvature.--Jay Lake, Technical Director, Briot

Losing the Bevel

Problem: Our wrap-around sunglass jobs don't seem to turn out too well. The bevel falls off almost every lens we cut for these frames. How do we prevent this from happening?

Solution: If you're using a free-float edger, you can have problems. A lens with a large curve can lose the bevel on this kind of equipment. A controlled bevel edger is better for high-base-curve jobs because it is mechanized and holds the bevel wherever you want it placed.--Mark Dehn, Sales Manager, AIT Industries

Frame Tracers and Wraps

Problem: When we make an Rx for wrap-around sun frames, we have a problem getting the frame tracer to work right. Why is this, and what can we do about it?

Solution: The tracer can't trace both lenses at the same time for a frame with a lot of curvature. Instead, put the eyewire of one lens into the edger and keep the other eye out so that you're tracing the frame monocularly.--Clark Smith, Regional Sales Manager, Santinelli International

Dye Temperatures

Problem: When we tint pairs of sunglass lenses at the same time, sometimes the two lenses come out different colors, even when the Rx's are close. We're not doing anything different to one lens in the pair, so I can't figure out why this is happening.

Solution: Make sure that you check the temperature of the dye unit frequently during the day. The tint temperature must be kept where the manufacturer specifies -- usually just below boiling. If the temperature is kept too low, the results can be inconsistent, even when two lenses go into the same dye bath at the same time.--Tim Dixon, Technical Services, WECO International EB

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