LATHES/ TURNING CENTERS

Making Contact 
Lenses Requires Ultra 
Precise Machining

A small piece of plastic resting on the cornea helps millions of people see more clearly, and a lot more comfortably. Contact lenses need to be precision-crafted to improve vision while allowing the eye to breathe normally. Making these contact and intraocular lenses properly depends on a company in Carpinteria, CA called DAC Vision, a world-leading manufacturer of two-, three-, and four-axis CNC (computer numerical control) lathes, including the Series III/4XC. The 4XC is a four-axis, ultra precision diamond turning lathe. This lathe’s left-hand diamond tool removes most of the material, which is blocked or held directly by the collet, while it forms the contour. Then the final cut is made by a second tool. The 4XC is equipped with a contact lens software package that provides edge radius input for producing reliable, repeatable radii for spherical and aspherical designs. The typical machining time is less than 60 seconds per side.

The ultimate goal of the 4XC, besides precision, is to produce a lens that is comfortable for the contact wearer; and this depends on the shape, lift and thickness of the lens edge. According to Jim Drain, DAC Vision’s Vice President and Managing Director - Santa Barbara, "Performance is not just nice surfaces; our customers’ eye care professionals must be able to improve their patient’s vision."

Since 1980 DAC Vision has depended on Russell T. Gilman, Inc. of Grafton, WI to provide cast iron dovetail slides (Gilman models DC6, DC8 and DC 10, in 6", 8" and 10" widths) for its lathes. These slides have given their lathes the absolute accuracy, stability and ultra smooth vibration-free motion needed to make the lenses properly. The slides are fitted with lead screws, bearings, plates and accordion way covers. Drain says, "In our applications it is critical that mechanical resonance and electrical noises do not find their way to the lens surface. Gilman cast iron dovetail slides really do the job."

Gilman slides are used as a positioning stage by adding brushless motors, rotary and linear encoders, and cabling to the machine control. This combination enables the slide to operate with 0.1 micron resolution from the linear encoder to ensure absolute positioning; and 0.050 micron resolution from the rotary encoder to synthesize the tachometer and provide the best possible resolution during the cut cycle.

Russell T. Gilman, Inc. is a global supplier of high-precision machine modules, including cartridge and block spindles, integrally motorized spindle systems, roller bearing and hardened steel way and dovetail slides, index tables, multi-axis modules, and customized modular components.