Jun
2006

The Art of Beveling

 

Lab experts agree that today’s computerized edgers do a good job of shaping and placing bevels on most lenses automatically. “It’s a lot different then when I started in the 1960s,” says Bill Rosser, optician-owner of Rosser Optical in Williamsburg, Va. “We had to create bevels by hand back then, working with glass lenses that cracked easily. There was a lot of waste.” Now, says Rosser, computerized edgers produce good bevels consistently with less handling and breakage. While automated systems have made the task of beveling easier and faster, it still takes an experienced lab technician to set up the lab protocols needed to deliver high-quality results across the current wide spectrum of lens and frame jobs. Some specialty jobs such as sports goggles and odd frame shapes also require the masters’ touch at the hand stone for the perfect finish.


Beveling Basics
The term “beveling” applies to two different steps in the lens finishing process, edge beveling and safety beveling. Edge beveling refers to the process of rough cutting a lens down to size and creating an angled edge or bevel that fits securely into a frame bevel track. Safety beveling is a final step that smoothes out any sharp points along the beveled edge for “safety” in handling and wear. It’s also called pin beveling because it requires a very light touch that takes off no more than the thickness of a pin. Both edge beveling and safety beveling are executed by automatic edging equipment. While edge beveling is done universally on automatic equipment, some opticians prefer to safety bevel by hand, either because their edgers lack the built-in safety bevel feature or simply because they are good at using a hand stone to achieve a high-quality finish. These skilled professionals remove the lenses when the edger completes the beveling and polishing cycles and manually apply the safety bevel with a handstone, also called a hand edger or touchstone. The hand stone, once the mainstay of the craft, is used now mainly for safety beveling and a few specialty jobs that require hand beveling post-edger. The hand stone has one or two rotating diamond wheels on which the operator manually refines the bevel shape and applies the safety bevel. The operator’s expertise lies in applying the right amount of pressure on the lens against the spinning wheel. Too much pressure will ruin the lens while too little might leave sharp edges. Accurate bevel placement and a high-quality finish are important in meeting consumer expectations for safe and cosmetically attractive eyewear. No patient returns a pair of glasses complaining about the “bevel.” But when patients return their eyewear because they are unhappy with their appearance, the problem might relate to the bevel placement.


Automated Technology
Today’s automated edgers provide a range of features that help to execute the correct bevel angle and placement on the lens. Edger software transfers data from a frame tracer that includes variables such as frame width, height, curvature, thickness and sometimes the frame bevel angle. These frame measurements plus the patient’s PD and prescription data are combined with accurate lens layout and blocking to enable the equipment to create a bevel that fits the frame perfectly. The lens material is also factored into the processing equation. Most edgers have selections for plastic, polycarbonate and glass. Newer models offer settings for PPG Industries’ Trivex material, anti-reflective/hydrophobic lenses and fragile lenses. These settings automatically adjust the process speed and clamping pressure electronically based on lens type. On edgers without these options, the speed and clamping pressure must be adjusted manually based on the characteristics of the lens being beveled. Computerized edgers identify the optimum bevel automatically and also provide customized bevel options for jobs requiring operator adjustments, such as unusual frame shapes, thick lens edges or special prescriptions. Custom bevel settings include percentages like onethird/ two-thirds and 50-50, as well as positioning on the front face, rear face, frame curve or base curve. An image of the lens edge appears on the edger’s monitor screen so the operator can see the bevel placement and make adjustments as needed.


Hand vs. Machine

“I have to admit that 98 percent of the time, I cannot manually choose a bevel position that’s any better than the computerized edger chooses automatically and that’s with 30 years of experience,” says Michael Fish, an optician who owns Optical Fashion in Fishkill, N.Y. “For the first 20 years of my career, a big part of my job was hand beveling. I still love the hands on stuff, but the only time I need to do it now is with specialty jobs like half eyes and odd angles,” adds Fish. The number of jobs that involve manual adjustments or hand beveling in a retail lab will vary based on factors such as the skill level of the technicians and the types of jobs edged. Some shops do a lot of specialty work like sports goggles and have the experienced personnel to hand bevel these jobs. “Scuba goggles and some nylon sunglasses require a steeper bevel,” notes Rob Tribble, an optician with Tom Barrett Optical in Dallas. “We rough cut the lenses to a slightly larger size on the edger and then finish them on a hand stone to get the lens bevel steeper on the backside so that if anything impacts the lens, it will come out the front.” The age and capabilities of a lab’s edging equipment also affect the amount of handwork that’s done. Machine technology varies widely, running the gamut from edgers that do basic beveling with few bells and whistles to the high-end multifunctional equipment engineered to handle all kinds of specialty lens and frame materials at the push of a button. The need for manual bevel adjustments decreases inversely as machines get increasingly sophisticated, reducing the skill level needed for expert beveling.


Beveling Techniques
The current crop of premium lenses are expensive and beveling errors can be costly. Following some guidelines designed to avoid spoilage and achieve a highquality bevel consistently across the full spectrum of jobs.


Learn from the experts—the lens manufacturers and equipment manufacturers who developed the materials and machines. Chris Bowers, operations manager for the Walman Optical lab in Minneapolis, points out “the engineers for the equipment companies who developed the technology are the real experts on explaining what it can do and how to use it.” Lens manufacturers are also eager to provide recommended beveling guidelines. Contact these suppliers especially when beveling a lens or frame product for the first time. Another good source of information for retailers is your wholesale lab contact. Big labs are often on the front line of learning about new lens materials and processing technologies.


Inspect the lenses, frame and patient information at the start of each job to identify any special handling requirements, such as protective pads for ARcoated lenses. This basic step can help avoid mistakes. According to Bill Rosser, the key to achieving a quality bevel is being meticulous with your job specifications and running a clean operation.


Keep all equipment and accessories clean, including job trays and the work area. Debris accumulating on an edger or blocker can transfer to the lens edge, causing it to spin off axis and ruin the bevel. Automatic edgers use water or vacuums to remove swarf and debris during cycling, but all equipment needs to be cleaned on a daily basis along with any filters and water pans. Check with equipment manufacturers for guidelines on maintenance.


Know your equipment.Machines have strengths and weaknesses, and even personality quirks when it comes to beveling various lenses and frames. Master optician Michael Fish observes that his edger cuts highindex materials slightly larger than the specified size, so he’s learned to adjust the sizing accordingly. “I know exactly how my machine will handle certain materials and even certain brands,” he notes. This helps him determine the best beveling techniques.


Use trial lenses to “test run” a bevel placement on difficult jobs. It’s worth the effort to save the expense of ruining an expensive pair of lenses. Keep old scratched and discarded lenses around for this purpose.


Beveling Guidelines
Following are some beveling guidelines for different types of jobs.

Polycarbonate: Select the polycarbonate setting or the “soft bevel” or “fragile” setting. The goal with soft lens materials is to reduce torque by decreasing clamping pressure and slowing wheel speeds to help avoid spoilage. Polycarbonate should be rough cut dry and beveled wet to reduce swarf (a gummy build-up from lens material removed in cutting). Wet edgers with a poly setting provide the wet-dry cycles automatically.

Trivex: Use the Trivex setting or check with your equipment manufacturer and the lens manufacturer for processing recommendations. Although some labs use the polycarbonate setting, others use the fragile lens setting. It’s best to get expert advice for your machine.

Polarized: Use the fragile setting to minimize risk of delamination. Automatic edgers do a good job placing the bevel. Thick highminus lenses may require adjusting the bevel forward to avoid any exposed edges on the front rim.

AR Lenses: Anti-reflective lenses, loved by patients for their visual and cosmetic benefits, are the nemeses of the lab world due to their slippery hydrophobic surfaces that can slide off axis during processing. Crazing and cracking may occur, especially with thin high-index lens, and the result is a very expensive redo. Some retail shops send their most difficult AR jobs to commercial labs to avoid the costly risk.


Newer edger models now offer a hydrophobic setting that automatically adjusts process variables to avoid slippage during the bevel cycles. Labs use various kinds of self-adhesive protective pads applied to the front and back surfaces of the lenses, under the chucks, to protect the lens from scratches and reduce slippage.

More AR handling advice:
Use the type of protective pads, stickers or seals recommended by the lens maker, and check for any pre-applied lens protective layers.
Apply protective pads smoothly with no wrinkles and keep them inside the finished lens shape to avoid contact with the beveling wheels.
Place the block firmly on the center of the non-slip protective pad or sticker, and block on the optical center using softer non-metal blocks if possible. Check first with your edger manufacturer for blocking guidelines compatible with your machine.

Make sure the base curve of the block matches the lens base curve. “Our blocks are concave to fit a generic base curve,” notes Rob Tribble. If there are any gaps, “we use a piece of protective pad to fill the cavity so the center section of the lens fits better into the block.”
Handle the lens by the edges and avoid brushing against the surface. Tribble is careful not to wipe the front surface of the lens during layout. Use translucent pads that show markings.

Use the AR setting or the “fragile” or “delicate” setting designed to reduce clamping pressure and machine speed. The idea is to slow down the process to reduce torque against the lenses and avoid slippage while beveling.

Unusual Frames and Rxs:
Very small frames, half eyes and frames with odd angles and corners present a beveling challenge depending on the edger used. Even small chucks are often too large for some of these jobs. To bevel odd shapes, Michael Fish rough cuts as small as possible on the edger, and then completes the bevel by hand on a handstone.

Harry Chilinguerian, optical manager for Young Eyes Optical in Baltimore, a practice specializing in eyewear for young children, has a lot of experience with small frames. When beveling children’s eyewear, he switches his edger to the passive setting to decenter and block the lenses manually. “If we don’t do that, the block comes in contact with the wheel and shifts off, so the bevel isn’t straight.”

Special Rxs often require customized bevels. When creating eyewear for conditions like anisometropia, where there is a difference in power and lens thickness between the right and left eye, Chilinguerian customizes the bevel placements to compensate for the base and vertex differences, moving the bevel forward on one lens and back on the other.

With a combination of automatic beveling and processing techniques developed by the optical masters, labs today are able to achieve optimum beveling results with a broad spectrum of eyewear. Both consumers and independent retailers benefit from this serendipitous partnership between technology and technical expertise.

LT

 

 

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