Edging Basics
What is the process of removing the majority of stock from a lens?
Roughing
What type of bevel places the apex in the middle of the lens?
V-Bevel
What does the index of refraction measure?
How efficiently a lens bends light
Which lens material is heavier — glass or CR-39?
Glass
Which materials must always be edged wet?
Glass and CR-39
What is the buildup of poly lens grindings called?
Swarf
Which bevel type hides the apex within the frame bezel?
Hide-a-Bevel
What does specific gravity tell you about a lens?
Its weight compared to water — lower value means lighter lens
Which lens material can be tinted easily and uniformly?
CR-39
Which materials can be edged either wet or dry?
Trivex and High-index
Which part temporarily mounts to the lens to hold it during edging?
Block or blocking device
Who trademarked the Hide-a-Bevel and in what year?
American Optical, 1969
Which lens material has the highest tensile strength?
Trivex
Name two advantages of glass lenses.
High optical clarity and scratch resistance
What happens if you apply too much chuck pressure to an AR-coated lens?
It can craze or crack the coating
Name the two main edging cycles.
Roughing and Finishing
Name the two variables that guided bevel systems consider.
Lens steepness (base curve) and desired bevel placement
A lens with a high index will generally be ___ in thickness but ___ in reflections.
Thinner ; Higher
Why did polycarbonate require a hard coat after manufacturing?
It is softer and scratches easily without it
Why should drilling be avoided with polycarbonate and CR-39 lenses?
Low tensile strength can cause cracks
Why should a plastic/poly roughing wheel never be used on glass lenses?
It can damage the wheel and lens because glass requires a harder, wet wheel
Why might a plus lens require a front-biased bevel?
To reduce lens thickness and improve cosmetics in the frame
Which property is measured by the force required to pull a material until it breaks?
Tensile Strength
Which lens material was originally developed for aircraft windshields in WWII?
CR-39
During hand edging, what is the purpose of “rolling” a lens edge?
To smooth sharp edges and prevent chipping