|BUILT-IN DRILL Coburn’s Exxpert HPE-8000|
|HIGH BASE CURVE Essilor Instruments Mr Blue|
|DRY EDGING National Optronics 7Ex edger|
|HIGH PRODUCTIVITY Briot Alta Zd|
|COMPLEX DESIGNS Optek Shape|
Modern edgers can process high-index lens materials in minutes.
With the press of a few on-screen icons, modern edger systems finish a variety of high-index lens materials in record time. Behind this seemingly effortless process is some serious technology. Here’s how they do it.
Contemporary diamond wheels use smaller diameters and coarser grits than previous versions. They are wider and spin at an optimal speed for the material selected. They often have diagonal cooling slots or holes on the grinding surface to keep the temperature down during grinding. Due to the elasticity of Trivex‘ material and polycarbonate, the wheels will cut these materials dry rather than with coolant flowing to reduce torque (see “Coolant Cycle,” below).
In the case of National Optronics, Inc.’s 7Ex, all edging is done dry using a router-type blade cutting system that works well on all plastic materials. With Coburn Technologies, Inc.’s Exxpert HPE-8000, Briot USA’s Alta Zd, Mr Blue by Essilor Instruments USA, Santinelli International, Inc.’s Me 1200, AIT Industries, Inc.’s Weco E.6, Optek International’s Shape, and similar machines, initial shaping can be accomplished using the built-in drill/mill that hews the primary shape to within a couple of millimeters of the finished diameter.
Once chucked, a lens is mounted onto the lens spindle (shaft) of an edger. The rotation speed of the lens spindle (and subsequently the lens) can be slowed, rocked back and forth (reversing rotation), and revolve more, taking only a little of the material and a bit of the lens’ diameter with each rotation. Any or all of these functions may be used on thick and stubborn materials to reduce slippage.
Except for milling or blade-type edgers, liquid coolant flows from start to finish when high-index resin lenses and CR-39‘ lenses are selected. The same is not true for Trivex material and polycarbonate. As previously mentioned, these materials are cut dry during the roughing and first beveling cycles. This cycle also causes either a vacuum to remove swarf from the chamber or a high pressure rinse. Coolant is introduced only after the bulk of material is removed and the lens edge needs a finishing touch.
Multi-layer super hydrophobic lens coatings do not like to be flexed. Too much chucking pressure can cause these lenses to “bruise” or craze if it flexes. Too little pressure can cause slippage, resulting in misaligned segments and cylinder axis errors. New systems have touch displays that allow you to choose the material to edge, which tells the computerized chucking system how much pressure to use.
Flexible plastic edging blocks specifically designed for irregular base curves are recommended for use in most new finishing systems because they conform better to the shape of the front surface of the lens rather than causing it to bend. New edging systems have special chucks that precisely align with these flexible blocks and evenly spread the chucking pressure over a larger portion of the block, thus reducing lens flexure.
These four functions prevent lens edge chaffing, axis slippage, crazing, and spoiled lenses. You might do well to build a long-term business plan for your shop that includes one of these machines.
Michael Frandsen is the owner of Quality Performance Ophthalmic, Inc., a custom service optical laboratory in South Jordan, UT.
|WHERE TO FIND IT:|
|AIT Industries, Inc.
|Coburn Technologies, Inc.
|Essilor Instruments USA
|Santinelli International, Inc.