ASK THE LABS
Q&A
by Karlen McLean, ABOC, NCLC

GETTING THE GROOVE

Q: Should I groove rimless lenses before or after I polish them?

A: It's best to process grooved rimless lenses in this order: Edge first, polish second, and groove third. By polishing lenses before grooving them, you eliminate getting polishing compound and other debris from polishing in the groove, which can cause lens spoilage. It also can make the groove more precise.

A lab that's invested in current high-tech equipment and trained operators can create state-of-the-art rimless lenses with much less effort and far more accuracy than doing rimless work by hand.

— Bob Lommerse, general manager, Toledo Optical Laboratory, Toledo, Ohio

RIGHT ANGLE

Q: When I'm drilling a hole for a rimless screw-type mounting should I drill the hole straight or at an angle? Does the direction differ with poly, Trivex, or 1.67 lens materials?

A: The direction of holes in a rimless drill mounting isn't dependent on the type of lens material, but is dependent on the base curve of the lens.

You should almost always drill the direction of rimless holes to the angle of the lens; the holes should conform to the base curve of the lens. Newer rimless drills feature tilt tables with various drill angles that make rimless drilling much easier and more foolproof, while older rimless drills must be manually operated.

— Kevin Bargman, president, Hawkins Optical Laboratory, Inc., Topeka, Kan.

DEVIL OF A BEVEL

Q: What types of rimless bevels are typically utilized in today's eyewear?

A: The most common rimless bevel is a flat edge with a pin bevel on both sides, which is a traditional rimless bevel. For string-type rimless lenses, it's a flat bevel with a groove. Fancier custom rimless lenses like scallop-shapes are flat edge pin beveled, while faceted-type rimless lenses feature custom-worked edges.

While today's lenses generally tend to be "thinner is better," in a faceted rimless, there has to be some thickness to the lens in order to maintain the facet, not be too sharp, and avoid easy flaking.

— Ron Schlotzhauer, vice president/general manager, South Central Region, Essilor Laboratories of America

CHAMFERING at the Bit

Q: I've heard the term "chamfering" in regards to drilling rimless lenses. What does it mean? How can I go about chamfering my lenses and when is it appropriate?

A: Chamfering is the term used when you smooth out the surface around a drill hole in a lens. This is done with a specially shaped file that fits partway into the drill hole.

All drills leave a rough surface and small fractures around the edge of the drill hole. Cleaning up those rough surfaces and fractures helps reduce splitting and chipping around the drill hole.

—Steve Seibert, president, Three Rivers Optical, Pittsburgh

If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean. E-mail: mcleank@lwwvisoncare.com. Fax: 215-643-1705. An archive of past Ask the Labs columns can be found on the Eyecare Business Website at www.eyecarebusiness.com.