This section provides tips and techniques for sizing and beveling lens made with Trivex material to fit a frame. Also addresses grooving a lens to fit a rimless frame.
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Finish BlockingA high quality pad should be used to block lenses made from Trivex material. Pads that stretch too easily may cause axis problems. Also remember, the smaller the diameter and the thinner the lens blank edge is, the less torque there will be in the edger, helping to keep things on axis. Be sure to use the correctly curved block for the lens’ base curve.
Lenses made from Trivex material have a little flex in them so using the wrong shaped block may damage the lens when it is chucked in the edger. Flexible plastic blocks work well to reduce this problem but avoid using older over-used plastic blocks that could cause axis problems. Chucking pressure should not exceed 20 psi or be less than 18 psi or the metric equivalent of 80kg.
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Edging – For Dry, Blade Style Edgers A dry, cutter blade edger provides excellent edging results with lenses made from Trivex material. Good sharp cutter blades will not only cut the lenses easily and with very little additional torque, they will also produce a semiglossy edge that some technicians feel needs no additional edge polishing. For semi-rimless chord mounted jobs, it is advisable to use the semi-rimless blades that automatically groove the lenses, if possible. This saves time and an additional step in the groover. It is also not necessary to clean out the melted swarf that accumulates in a manual groover with Trivex material. An airborne particulate and a distinctive smell can be created when edging lenses made from Trivex material. To help reduce the particulate and scent, use a dry-cut cycle that has a vacuum to collect the dry swarf if possible. It may be advisable for lab techs to wear a dust mask during the edging and surfacing process.
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Edging – For Wet-Sump Diamond Wheel Edgers Having a wet edger with the correct diamond wheels is one of the most important factors in getting lenses made from Trivex material to finish on axis and with a high quality bevel. The recommended diamond wheels have diagonal slots or a series of holes in either of both the roughing wheel and the beveling/finish wheel. The purpose of these slots/holes is to allow for cooler roughing and beveling cycles. The diamond grit on these wheels is very much like the grit on conventional polycarbonate stones and they work well on all types of plastic lenses. If the edger has a “Trivex” setting it should be used. Most older edgers will not; in which case the, polycarbonate setting will work best. Lenses made from Trivex material should be rough cut and rough-finish cut dry (without the coolant water running on the wheels). Coolant water should be running on the final finish edging cycle to bring the bevel to a smooth finish. If the machine has an edge polishing wheel, use the coolant water on this cycle, too. There will be a noticeable amount of melted swarf coming off the lenses during the rough cycle which can form into hard chunks. These fragments may clog the swarf drain in the edger if the machine does not automatically wash them away. They can also get wedged between the diamond wheels and the grinding chamber walls, causing a loud bang when they dislodge and propel back into the grinding chamber. Because of this, it’s important to be very cautious and wear safety glasses while edging lenses made from Trivex material.
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Sizing and Bevel Placement Lenses made from Trivex material maintain their size and shape well over time and do not need to be edged large to compensate for shrinkage like some materials. Cut these lenses right on size. Trivex material hand edges slowly on conventional grit ceramic-pin-beveling hand stones. Use a dual grit hand edger stone with a coarser grit on one side and a finer grit on the other side in order to hand edge it effectively.
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Manual Edge PolishingThe automatic edge polishing function (on edgers that have it) give lenses made from Trivex material a shiny luster and is a convenient way to edge polish these lenses. For labs that use manual edge polishing equipment, use a fresh, new felt polishing pad or muslin buffing wheel in conjunction with a high-quality dry polish stick designed for polycarbonate. This dry polish has a lubricating wax in it that will help keep the lenses from getting pits in them from too much heat. Always protect the lens surfaces with surface protecting tape before polishing. Use as little of the polish stick as possible and use very little pressure when polishing. Avoid polishing the apex of the lens bevel, if the lenses were cut exactly to size, or they may turn out too small. Manually bringing lens edges to a high gloss takes a little time so be patient and do not overheat the lenses or they will blister.
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Manual Grooving
Manually groove lenses made from Trivex material dry (without using water). After grooving, clean the excess swarf out of the groove with an optical screwdriver, or similar device, the same way as with polycarbonate. This removal will be a little easier with Trivex material than it is with polycarbonate because the swarf comes off in long strands.
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Mounting and Inserting If properly edged and sized, lenses made from Trivex material will have a high-quality edge enabling easy glazing. These lenses should not be glazed too tightly or they may warp, causing distortion and stress aberration.
Be cautious when glazing lenses made from Trivex material into plastic frames using a heating pan containing glass beads or salt. Excessive heat can blister the lenses, so a hot air frame warmer is recommended for this task.
Use standard mounting and insertion techniques to glaze lenses made from Trivex material into metal and semi-rimless frames.
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