Glass Cutters
There are a large number of styles and types of cutters available on the market. It is best to get the feel of one before buying. You can try various styles out in classes, and usually shops will have examples for demonstration.
Simple steel wheel cutters |
The cutters above are inexpensive and that is the only advantage. The one on the left with a turret of wheels is unsuitable, as the need to have a number of spare wheels might indicate. It also is unsuitable as its design obscures the cutting line in use. The cutter on the right is a traditional plain steel cutter with notches for grozing different thicknesses of glass. It is better, but because of its large wheel, requires more pressure to create the score.
Oil filled pencil type cutters |
Toyo thumb grip and a generic pistol grip cutter |
Glass Cutter Wheels
There
are many different types of glass cutters on the market today.
Choosing the proper cutter is the most important decision you must
make, as it will be a large element of how you enjoy scoring and
breaking glass. There are some elements that you should consider in
addition to the style of the holder.
Steel
Wheel Cutters
are inexpensive but usually not long-lasting. They must be replaced
frequently as they easily become damaged.
Tungsten
Carbide Cutters
are more expensive than steel wheel cutters, but far outlast them in
durability. Self-lubricating cutters eliminate the need to constantly
lubricate your cutter between scores.
Wheel
Angles.
There are steel wheel cutters which are good for general purpose
cutting, production cutting, or pattern cutting. Some are good for
cutting thinner glass, others for thicker glass. The angle of the
bevel on the wheel determines this and differs from model to model,
although some offer wheels of different angles. Pistol grip cutters
produce more pressure than others.
Cutting Wheel Angles*
These
are the wheel angles recommended by The Fletcher-Terry Company for
various glasses:
114
to 134 degrees – 2mm float glass
130
to 140 degrees – 4mm float glass
134
to 140 degrees – 3mm to 6mm float glass
148
to 154 degrees – 12mm to 25mm float glass
This
suggests that wheel angles of 134 to 140 degrees are suitable for
stained glass work.
Wheel
angles of 88 to 114 degrees are suitable for borosilicate glass.
The Effects of Wheel Angles on Glass Cutting*
Measurement
of angle
The
wheel of a glass cutter does not “cut” the glass. The objective
is to create a crack or "fissure" along which we expect the
glass to break when we bend it. The idea is to produce a fissure
which is continuous, and of uniform depth, without creating a flaky
score line full of loose glass chips. While the wheel angle is only
one of several variables which influence the quality of the fissure,
it is the best place to start. The other main variables are wheel
diameter and cutting pressure. The angle is identified as the
included angle to which the apex is honed. This means it is measured
from one beveled face of the wheel around through the wheel to the
other face. Thus the angle between the wheel and the glass on a 150°
wheel will be 15° on each side.
Cutting
Pressure
When
downward pressure is exerted on the wheel rolling along the glass,
forces are created which radiate down and slightly to the side trying
to shear or separate the glass along the surface. If these forces are
great enough to overcome the inherent compressive conditions near the
surface, a crack will be generated along the path of the wheel.The
direction of these shearing forces is determined by the wheel angle.
A
wheel with a large or blunt angle produces shearing forces that tend
to be directed downward more than to the side. It would require a
great deal more cutter pressure to create enough lateral force to
overcome the compression in glass. This explains why a cutter
requires more pressure as it gets older. The apex tends to flatten so
its effective angle becomes greater.
With
a very sharp wheel angle, the shear forces are directed more parallel
to the surface of the glass. This suggests it is easier to produce a
fissure with a sharp wheel than a dull one. The shear forces are
directly opposing the compressive condition near the surface of the
glass therefore, requiring less downward pressure to make a crack.
A
sharp wheel tends to cause chips and a flaky score. If the shear
forces run close to the surface of the glass they are more likely to
cause a lateral crack which then breaks out to the surface, creating
a chip. You can see these chips leap out of the glass a minute or so
after scoring. Again, the compressive condition of glass near the
surface literally squeezes the fissure closed, spitting out loose
chips. They can be seen lying on top of the glass.
Effect
of wheel angles on the cut edges of glass
Another
factor to consider in selecting the proper wheel angle is the "edge".
The objective of good glass cutting is to produce an edge which is
flat and relatively free of irregularities such as "shark
teeth".
Shark
teeth are the occasional deep spikes in the edge and are accompanied
with flakes or tiny chips on the surface. A three mm thick glass
scored with a sharp wheel (114°) will produce this effect. This edge
irregularity may lead to failure during the life of a window.
A
three mm thick glass scored with a proper angle (134°) of wheel,
will produce a fissure that is made up of individual "hackles"
which overlap one another. They have a unique semi-circular shape and
indicate the direction of the cutting wheel. With proper pressure the
edge will be relatively free of irregularities and without shark
teeth.
The
effect of glass thickness on cutting
Most
of the thicker glass being used today is produced by the "float"
method. In this process the glass travels horizontally from the
furnace, through a molten tin bath, through annealing lehrs, then
continues on rollers where it is inspected, scored and broken into
the sizes required. The thickness generally dictates how fast the
ribbon of glass moves. The thicker the glass, the slower it is
processed and the more effective the annealing. This applies to
thicker art glass too.
The
key to subsequent cutting is the annealing cycle. Thicker glass tends
to have less compression at the surface and tension in the interior.
As a result, the glass cutting wheel encounters less resistance to
producing a fissure with the shearing forces. However, this means the
glass surface will chip more readily. Therefore, a larger wheel angle
is required to prevent chipping. It is also common practice to use a
larger diameter wheel and larger angle so the fissure can be driven
deeper without chipping.
Cutting Oil*
No
matter how good a fissure is when scored dry, it is better if scored
with a liquid between the wheel and the glass. Several good things
happen with an "oil" cut and only one undesirable thing.
The
bad thing is you have to wash the glass afterwards, but in many cases
washing is required anyway.
A
good thing is the fluid reduces the effect of healing - the
compressive strength overcoming the fracture caused by scoring. It is
probable that the liquid seeps into the fissure contaminating it
enough to prevent atomic reattachment of the molecules.
Cutting
oil reduces chipping and prevents a flaky score line. The oil tends
to provide a hydraulic cushion between the glass and the wheel. This
allows more uniform transmission of the shearing forces into the
glass at an angle dictated by the wheel, not by particles of crushed
glass.
It
is important to check the cutter wheel is moving freely, since a
wheel not rolling freely may skid. Skidding causes abnormal wear to
the wheel and subsequently it becomes a skipper.
You
should not use kerosene or white spirit by itself because it removes
whatever oil is on the axle.
Breaking Pliers
Description
The
breaking plier is a special stained glass tool that has smooth jaws
that meet at the tip of the pliers. This enables the tool to reach
over the top and bottom of the glass with only the tip coming into
contact with the glass exactly against the score line.
Use
The
plier handles are held at a right angle to the score line. The edge
of the glass needs to be close enough to the score line in order to
use this tool, as the tip of the jaw needs to be against the score
line. It is used in lieu of your hands when the piece being broken
off is too narrow to be comfortably grasped by hand. When bending the
glass, the top jaw comes down flat against the surface of the glass
(that's the reason for the smooth jaw) and as the bending pressure is
applied, lateral/pulling pressure is applied at the same time. This
tool can also be used to groze the glass by carefully nibbling away
the edge.
Note
If
the score line is further than 20mm away from the edge, cut running
pliers are usually the appropriate tool to use.
Combination grozing and breaking pliers
Description
The
jaws of grozers are serrated and used to gently remove small pieces
of glass which remain after the glass has been scored and broken.
They are normally supplied with one straight jaw and one curved
making them combination grozing and breaking pliers.
Use
as breaking pliers
When
used as breaking pliers the flat side should be up and the nose of
the jaws almost touching the score line. The breaking pressure should
be down and slightly to the side to bend and pull the piece away from
the main piece of glass.
Use
as grozers
When
used a grozers – to gently wear away some small part of glass - the
curved jaw should be up. The plier jaws should be used slightly open,
and a downward motion of the plier does a “rasping” of the glass
edges, taking away small bits of glass. With experience, a lot of
glass can be removed quickly shaping the glass with a fair degree of
precision. The edge can then be tidied by a grinder if required.
Cut running pliers
These
are intended to assist with the running of long straight or gently
curving scores.
Description
These
are pliers with curved jaws. When looking at the pliers from the nose
toward the handles you will see the curve like a down turned mouth.
These assist the breaking of the score by putting tension on the
glass.
Cut
running pliers almost always are supplied with covered jaws. This are
normally two pockets of flexible plastic that fit snugly onto the
slightly flared, curved jaws. Keep these on. When worn they can be
replaced by buying more, or by wrapping the jaws with tape, using
"liquid plastic", or sometimes, even using them bare.
There
is a spacing screw on top which allows adjustment for different
thickness of glass. It is intended that the jaws should not close
completely – which can place excessive pressure on the glass –
but be adjusted so that there is about 1mm less opening than the
thickness of the glass. So when cutting 3mm glass there would be a 2
mm gap. On 4 mm glass the gap would be 3 mm, and so on. experience
will show what relationship is best for you. The principle is that
the pliers perform a gentle tensioning of the glass. Using your hands
exerts more tension on the glass and cannot be so delicate.
Use
Align
the centre of the top of the jaws - often the pliers have a centre
line on the top to assist – along the direction of the score.
Squeeze gently and the score will begin to run.
I
have found my best success when using cut running pliers is to avoid
trying to run the whole score from one end. With a bit of practice
you get the feel for how much pressure you should be applying and so
when to stop. Then turn the glass around and start the run from the
other end. Usually the open ends of the score will meet and the break
is completed. Occasionally the two runs will not meet. Then it
depends on how complicated the curve is as to whether you use your
hands to complete the break or start tapping the score line to finish
the break.
Pattern Scissors
The
purpose of pattern shears/scissors is to cut out the space between
pattern pieces equivalent to the came heart or the space needed for
foil.
The scissors come in two thicknesses – one for leaded
and the thinner for copper foil.
Alternatives
to pattern scissors
For
copper foil, you can use normal scissors, by cutting to the inside of
the pencil or inked line. You can also use a scalpel or craft knife
to cut to the insides of the marked lines.
For
leaded glass you can use a felt tip pen (a bullet point is almost
exactly the right width when new) to draw the cartoon or template.
Then cut with scissors or a craft knife at the sides of the line.
Glass Cutting Surfaces
Make
sure you are putting the glass to be cut on a smooth and level
surface with no glass shards. If the surface is uneven, it will give
difficulties in scoring and breaking. The tell-tale squeaks as you
move the glass indicate there is other glass under the sheet. These
shards and any other small almost invisible things under your glass
can promote unwanted breaks. Also, if there is glass or other grit on
the surface, it may scratch the glass. So make sure you brush the
cutting surface clean frequently, and ensure there are no bumps.
Many
people have a slightly cushioned cutting surface. Some use short pile
carpets or rugs, others use thin rubber or foam sheets, others use
dining table protectors. All these are useful for cutting large
pieces and have advantages and disadvantages.
Carpets
and foam can trap shards of glass, so have to be cleaned very
carefully to avoid retaining sharp glass within the pile or foam.
Smooth,
wipe-able surfaces avoid trapping glass, but can be slippery. Choose
one with a non-slip surface.
It
is better to cut small pieces on smooth hard surfaces, as the
flexible surface will not provide overall support, and so allow
breaks, especially on long thin pieces.
Clean
the glass, at least along the cut line, as this makes the action of
the cutter smoother. The grit on the glass actually interrupts the
action of the wheel, so you get a staccato effect in the score line.
*This
section has been prepared from information provided by the
Fletcher-Terry company: http://www.fletcherviscom.com/home.shtml
A group of highly dedicated and experienced employees form a dynamic team, The manufacture of Gear Cutting Tools, Broaches and Allied Products.
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Gear Shaving Cutters
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