Saving Fingers Using Cutting Edge Technology

by WOHe

Saving Fingers Using Cutting Edge

By Russ Lee

A major hazard of working in a solid surface or woodworking shop is
that most of the tools a craftsman uses to create beautiful
fixtures for the kitchen and bath are extremely sharp and
dangerous. Although fabricators will tell you that a dull cutter is
far more dangerous than one that is razor sharp, the fact remains
that all it takes is one slip on the table saw to cause serious
injury or loss of a finger.

Such were the ruminations of patent attorney Stephen Gass, while
working on a hobby wood project in his Portland, OR-based home
shop. “I was out in my shop one day and looked over at the table
saw,” says Gass, who also holds a doctorate in Physics. “I wondered
if it might be possible to stop a saw fast enough to avoid serious
injury if you ran your hand into it by accident. So, I did some
calculations. I figured out how fast it would have to stop, how
much force would be involved, and if it was a realistic thing to

What Gass came up with was a revolutionary idea for a table saw
brake that brings a blade to a full stop within three milliseconds
(that is three one-thousandths of a second) after encountering
human flesh. Even more amazing, the device can differentiate
between wood or plastic and your finger by measuring each
material’s electrical charge. That means an operator can freely
process materials for months on end without a pause in operation,
but as soon as his finger comes in contact with the blade,
everything comes to a speedy halt.

“The system detects a person’s capacitance, or ability to store
a charge,” Gass explains. “It is an inherent property of all
physical objects. The human body, because it conducts pretty well,
has the ability to absorb and store a charge quickly. But wood and
plastic don’t conduct very well, so their capacitance is low.”

Gass further notes, “We put an electrical signal on the blade so
that when you are cutting wood or plastic, nothing happens to the
signal, it just stays at the same level. When it runs into your
finger, your body absorbs some of the signal and it drops the level
down very quickly. In fact, before the first tooth leaves your
finger, the brake will have already tripped.”

Safety stop
The brake, which Gass has named SawStop, is best described as a
type of hermetically sealed plastic cartridge, which is mounted
about 1/8″ away from the face of the saw blade inside the body of
the table saw. Inside the cartridge, a brake shoe sits in front of
a very powerful spring, which is actuated when a sensitive fuse
wire is tripped. When the system detects contact with a finger, it
burns the fuse wire, which releases the spring very quickly and
causes the brake to make contact with the blade. The angle of
contact is such that once the brake hits the blade, it is
self-locking. Friction between the blade and brake pull the brake
more tightly against the blade.

Because the system is initially triggered by the blade coming in
contact with a human finger, the table saw operator will
necessarily receive a minor cut before the blade is stopped. But,
considering the typical consequences for getting a digit caught in
a rapidly spinning cutter, sustaining a little boo-boo is a small
price to pay for a lapse in concentration. 

“A saw blade makes one revolution in about 16 milliseconds,”
Gass observes. “For most people, it takes about 125 to 150
milliseconds to react and pull your hand away once your finger gets
caught. With an 80-tooth blade, that means close to 800 teeth will
cut into your finger before you can pull it out. With our system
installed, and using an 80-tooth blade, the blade would stop within
20 teeth. You almost can’t believe it until you see it for the
first time yourself.”

Another appealing feature of the SawStop system is that it is
installed below the table saw deck, which means there are no
bothersome guards to deal with. “It doesn’t affect the operation of
the saw in any way until you need it,” Gass says. “Then you would
be very, very happy it was there.”

The SawStop system is engineered to render the table saw
inoperative if anything goes wrong with the brake before or during
operation of the saw. For those materials that exhibit higher
capacitance characteristics (such as aluminum) that would cause the
fuse wire to trip, the operator may override the system for that
cutting cycle with the flip of a switch. On those occasions where
the brake has been actuated, a new cartridge must be installed
before the saw will become operable again, a simple operation that
Gass compares to changing the table saw blade.

Getting a brake
By now you’re probably wondering where you can go to purchase a
machine with the SawStop system installed. But, for that you will
have to be patient. “We don’t actually sell anything,” Gass says.
“Our goal is to license this technology to all of the different
manufacturers so they can incorporate it into their machines when
they build them.”

The folks at SawStop have been generating grass roots support
from the ultimate end-users of the product through participation in
industry trade shows. Once people see a prototype in operation,
Gass hopes they will apply pressure on the equipment manufacturers
to include it on their new machines.

“When we first took our idea to the manufacturers, we heard
things like, ‘Safety doesn’t sell,’ ” Gass says. “That is why we
debuted the product at the International Woodworking Fair in
Atlanta last year. Our goal is to make people aware of SawStop so
that they can go to the companies they buy their tools from and
tell them they want it. It is a very funny business model: No, we
don’t have anything to sell, but we are here at trade shows
promoting it, although there is nowhere you can get it

“We have gotten tremendous positive feedback from people. It is
applicable on other types of equipment as well band saws, jointers,
hand-held circular saws, mitre saws. SawStop can work on most of
the tools you could cut your finger off with in a woodworking

To learn more about SawStop, LLC, visit its Web site at, or call 503-638-6201.

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