Eyewear fashions come and go, but since their inception, rimless styles have remained steadfast on the optical scene. These mountings have gone through metamorphoses, from three-piece drilled rimless with glass lenses (in the days before case-hardening) to fancy facets and rhinestone accents, then back to plain lenses again. When the revolutionary "Logo" grooved semi-rimless constructions were invented, they represented the first new choice in rimless construction in centuries -- and they remain popular today.

To help you get the most out of this style staple, EB presents tips and tricks on processing rimless and semi-rimless lenses straight from the experts.

1. Stick with plastic. It's not worth it to try to put glass lenses into rimless or semi-rimless styles, according to Tim Dixon, A.B.O.C., technical services representative at WECO International. "Even if you case-harden a glass lens, odds are that it will break when it is drop-balled," Dixon says. "A grooved or drilled lens probably won't hold up to heat-treatment."

2. Don't forget to safety bevel. "Newer edgers automatically safety bevel the back of the lens," says Tracey Morrison, A.B.O.C., director of sales and marketing at Optical Works Corp. "But with rimless lenses, it's important to hand bevel the front of the lens for safety purposes."

3. Watch lens thickness. Watch lens thickness. When processing a plus lens for a rimless or semi-rimless style, make sure that the edges are thick enough to withstand drilling or grooving without chipping or breaking. That means that plus lenses, which are thicker in the middle and thinner on the edges, sometimes need to be ordered extra-thick.

"Generally, you want to have an absolute minimum of 1.5 mm of edge thickness," states Dan Kurban, service technician at LOH Optical Machinery. "Any thinner and the grooving or drilling can weaken the edge, and the lens will chip."

"You need to have sufficient ET to hold onto the lens securely when you're fastening the screw and nut," adds Gerber Coburn Product Manager Michael Urban. "When the temples open and close, there needs to be enough material there to hold up to the flexing." Urban recommends planning for a minimum of 2.0-2.2mm ET on plus lenses, rather than a knife-edge.

4. Stay away from certain lenses. Aside from glass, some lenses are better off mounted only in full frames. "Don't put executive bifocals into rimless frames," warns Morrison. "The executive is a one-piece lens, which means that the bottom half is always much thinner than the top, making it difficult to get sufficient ET for grooving or drilling. Also, the top portion of the lens sticks out so far that it's easy to chip because the groove has to be placed toward the back of the lens," she adds.

5. Don't cut corners when tracing demo lenses. Don't cut corners when tracing demo lenses. "When you're edging a rimless style, don't ever scan from a similarly shaped full frame instead of tracing the rimless demo lens," warns Frank Balestra, director of technical services at Santinelli International.

"When the machine traces a full frame, the stylus raises and lowers in 3-D measurement, learning the linear value and curvature of the frame to get the circumference," he explains. "But the sizing will be off if you use that method for a rimless frame. It's worth the extra couple of seconds it takes to mount the demo lens so that it will be traced properly using the dowel," he adds.

6. Take the easy way when drilling. Take the easy way when drilling. Instead of trying to be painstakingly accurate about drilling lenses by hand, the experts recommend using the equipment manufactured to make this job easier. Briot Edgers Inc.'s Technical Training Manager Gary Dean remembers back to the days when drilling was such a pain that opticians would hide three-piece rimless frames in the back so that patients wouldn't see them and order them.

He says Briot, like many equipment vendors, makes drills that resolve geometric center and axis problems. The drills use the block from the edger to hold the lens steady.

Matt Vulich, vice president, sales of A.I.T. Industries, concurs. "The newer drills secure and hold the lenses in place," he says.

7. Drill or groove polycarbonate lenses carefully. Drill or groove polycarbonate lenses carefully. "If you try to press the drill all the way through a polycarbonate lens the first time, you will push the material through and 'blow it out' in a hump on the back side of the lens," says Stuart Watson, director of training at National Optronics. "Instead, drill in half-millimeter depth increments, pausing a few seconds after drilling to allow the material to cool. This will result in a clean, smooth drill hole," he adds.

When grooving poly, Watson recommends making two to three passes around the lens. "Make the first pass at about half the final groove depth, then the second pass at the final depth," he says. "You don't want the poly to become super-heated, because then it will melt."

Watson also cautions that technicians should not drill halfway through the lens on one side, then turn it over to drill through to the middle from the other side of the lens. "It's difficult to find the same exact spot, especially on a high-Rx lens," he warns.

8. Think twice before faceting by hand. Think twice before faceting by hand. Bill Galindo, president of ODI/Topcon, says it might be better to send a facet job to an outside lab than to risk doing it in-house. "You need special equipment or a proficient optician to facet with a hand edger," Galindo points out. "Most modern machines don't have faceting features built in, so it's best to set the edger on the rimless mode to cut the lens shape, then send it out to be faceted. Even if the shape of the lens requires very sharp corners, most edgers will do a good job on that part of the job," he adds.

But if you do the faceting and polishing in house, you are the one taking the monetary risk should something go wrong with the job. If you send it out, the lab bears the financial burden, not you. EB