EYE ON EQUIPMENT

Getting an order for a "special" job can strike fear in the heart of the stoutest optical professional. These jobs are unusual enough that everyone from the dispenser to the lab technician is wary about processing them. If the measurements aren't taken correctly, the whole job will be off. Likewise, if just the least little something isn't performed properly in the lab, the job must be scrapped and the whole process begun again. So it's no wonder that the most experienced people approach special jobs with caution.

Fortunately, however, there are some steps that can be taken to process these orders smoothly. Here the experts provide some little-known tips and tricks to help you get the job done right the first time.

PROBLEM: Lenses for swim goggles don't turn out well on the edger

SOLUTION: A lot of hand work is involved in making lenses for swimming goggles. The lenses need to be edged on a flat bevel, and then a "ledge" has to be created by hand before the lenses are ready to be epoxied into the swim goggle.

The front surface of the lens has to be flush with the flat surface of the goggle. In order to do that, the back perimeter has to be shaved off all the way around in almost an "L" shape. Sometimes, older machines allow for the mechanical manipulation to do this on the wheel, but most people will have to take these lenses down by hand.

-Matt Vulich, A.I.T

PROBLEM: It's difficult to trace and cut lenses for polycarbonate safety frames

SOLUTION: These frames-and the lenses that go into them-tend to have a higher base curve than regular frames, so it's important that the tracer be able to work in 3-D. Likewise, three-axis control on a 3-D edger is best to cut these lenses. A free-float edger is not the ideal answer for lenses going into high-wrap frames. If you are using a conventional edger to cut safety glass, the wheels should be kept sharp because safety frames are thicker and the bevel placement needs to be more precise.

-Michael Urban, Gerber Coburn

PROBLEM: Glass safety lenses are difficult to process in the lab

SOLUTION: There are a few cases in which glass safety lenses are preferable to plastic materials-for X-ray technicians and welders, for example.

X-rays can't penetrate glass lenses. Also, hot sparks from a welder's torch can be removed from glass lenses, whereas they'll pit a plastic lens or become embedded in it. If you're making glasses for a welder, the glass lenses should be chem-treated rather than heat-treated. Chem-treating changes the actual composition of the glass to make the lenses stronger, whereas heat-treating hardens the surface of the lenses. Because glass is so heavy in a 3.0 safety thickness, high-index glass should be used. Any index is acceptable for safety glasses.

Extra care must be taken when processing glass lenses, especially when it comes to beveling. Glass has to be safety beveled on both the front and the back of the lens-you can't get away with just touching off the back the way you can with plastic materials. But glass is also easy to "bruise" when "safetying" it, so use a light touch, especially on the front.

If you're not in the habit of cutting glass jobs frequently, I recommend that you practice safety beveling an unneeded lens before attempting to tackle the real thing.

-Tracey Canada, sales and marketing, Optical Works Corp.

SOLUTION: The Porsche Carrera and frames like it have metal notches that the lenses fit into rather than using a bevel. The bridge is on a hinge, and it lifts up so that the lenses can be slid into the frame. If the power of the lens is greater than plano, it is necessary to do a "shelving edge" job. The edge comes down in an "L" shape instead of being beveled on a flat edge. The shelf can be created by hand using a file, or it can be done with a "shelving cutter."

On dry edgers, shelving cutters are shortened carbide steel blades with no bevel in them. The operator passes the edge of the lens over the tip of the cutter, which is cleaner and neater than doing the job by hand.

-Stuart Watson, training director, National Optronics

PROBLEM: The holes come out in the wrong place on three-piece rimless jobs

SOLUTION: It is a lot easier to get the holes in the right place when you're using an automated system. On some systems, the tracer and blocker work with the edger for precise placement of the screw holes. The blocker automatically "knows" where on the lenses the holes belong, and the operator simply confirms their placement by pressing a button. The blocker coordinates the drilling points with the edger, which cuts and drills the lens in one cycle.

-Kurt Atchison, North American sales manager, LOH Optical

PROBLEM: The bevel doesn't come out correctly on thin high-index lenses

SOLUTION: If the proper blocks aren't used, polycarbonate and high index lenses with a 1.2 center thickness can flex during edging, which causes erratic bevel placement. To avoid this problem, use the proper block for the base curve of the lens, or use a flexible block that will accommodate more than one base curve. Also, rough cut the lenses 4mm large, then bring them down to the correct size. This extra step is especially important with the newer patternless edgers because the lens curvature changes as the lens is cut down.

-Chris Martin, sales manager, Santinelli International

PROBLEM: Some high-index lenses crack during edging

SOLUTION: Mid-index lenses in the 1.56 neighborhood are a little more brittle than other materials, which can cause the lenses to crack in the edger. Especially if the Rx is a plus or low minus, or if there is a large difference between the A and B dimensions, you can cut down on breakages by using the "reverse rotation" option on the edger. This setting turns the lenses in the opposite direction from the way they normally rotate. The mid-index materials cut better in reverse rotation, and you see fewer lenses splitting in two. Also, it is helpful to reduce the edger's clamping pressure by about 25 percent when processing mid-index materials.

-Kent Jones, technical services, WECO International  EB

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