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Summary Information
taken in parts from "TECH N I TALKS'' a publication
of the Fletcher-Terry Company and reprinted by permission
The
technique for cutting glass with a hand cutter is very
simple. However, it will help if certain basic and easily
understood requirements are observed.
The
primary objective in glass cutting should not be merely
to sever the sheet but to score and break out so that
the resulting cut edges have good quality surfaces,
free of nicks and chips. A nicked or chipped edge is
a weak edge and often contributes to glass failure.
A
glass cutter does not and cannot cut glass in the sense
of shearing, sawing or routing. A glass cutter is a
force generator. By rolling on the glass surface, the
cutting wheel develops a system of forces in the glass
so that a minute fracture, called the fissure, is created
in the sheet. A good quality cut edge can be attained
at break‑out only if a proper fissure was made
by the wheel.
The
fissure which will yield a good, clean, and strong edge
is practically invisible when the glass surface is viewed.
However, it can be seen by looking into
the glass. The good fissure will reflect light and
appear as a continuous narrow band of light.
Cutting
force and speed are important and the force applied
on the cutter is dependent on the wheel angle, the condition
of the wheel and on the type and thickness of the glass
(more will be said about the wheel angle later). Regardless
of the angle, the maximum force which can be applied
is easily defined: it is the greatest force which can
be used without crushing the glass surface. The limit
is easily determined. When the score becomes a white
gritty line or if chips and glass dust are created,
then the maximum force has been exceeded. The resulting
line of score is a gouge, not a fissure. A good rule
is that the best score is clean of glass chips and barely
visible when looking at the glass surface.
Some
practice is required to get the feel of applying the
maximum force without crushing. It is essential to maintain
this force uniformly throughout the full length of score.
If the force varies then the depth of the fissure will
vary and affect the quality of break. This requires
practice but the technique is easily learned. When scoring
and applying this maximum non‑crushing force,
the score must be continuous until the wheel runs off
the edge of the glass. Forget the edge of the glass:
if you think about the edge of the glass as you approach
it, you will unconsciously vary the force and speed
of the scoring stroke.
The
depth of fissure is directly affected by the speed of
cut. The faster the wheel rolls, the deeper will be
the fissure. But there is an inverse relation between
force and speed. As the speed is increased, the force
must be decreased to avoid crushing and gouging. Generally,
the faster the score (below maximum non‑crushing
force), the better the cut. In hand cutting speed is
not as critical as in machine cutting. What is important
is that the speed be maintained uniformly throughout
the cut until the wheel drops off the edge of the glass.
If a good break‑out is not achieved, then a new
score must be made, with some increase in force. Never
retrace the line of cut. A score can only be made
once. Retracing only creates a gouge and damages the
wheel.
The
table surface is a very important consideration in cutting
glass. It is the surface on which the sheet lies. It
should be a hard, flat, and clean surface. It is recommended
that an easily cleaned resilient material be used to
cover the surface. A sheet of wrapping paper works well.
If a permanent cover is desired, it should be felt not
more than 1/16" thick. A thicker resilient cover
or a deflecting surface hampers good cutting. Cleanliness
of the surface is vital. The height of the table affects
the position of the person doing the cutting. He must
be able to make the score comfortably without having
to strain or change position.
The
objective in glass cutting is not only to sever the
sheet but also to attain a cut edge which is free of
nicks or chips. A chipped edge is often the cause of
glass failure. With a little practice the cutting of
a sheet of glass should be a relatively simple task.
There are a few simple techniques to the successful
cutting of glass. Understanding the principals of glass
cutting, following the techniques described in the following
paragraphs and a minimum of patience and practice accomplish
successful glass cutting by hand.
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