June 6, 2021
Statistics would not lie when it comes to grisly accidents due to the use of table saw. In fact, in the U.S. alone, ten amputations happen every day due to its usage. For this reason, companies like the Sawstops were established to raise the safety level in the use of the table saw a notch higher.
SawStop, as a company, popularized the concept of saw stop—The automatic stopping of the rotating blade of the circular saw when it hits flesh or skin. This automatic stopping of the blade happens in less than five milliseconds, preventing more severe injuries to the circular saw operator.
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Understanding the SawStop as a Company
SawStop, as an American company, was founded in 1999 in Tualatin, Oregon by Steve Gass, a physicist, attorney, and woodworker. His company was established to manufacture table saws equipped with an automatic braking system. This automatic braking system halts the blade’s rotation upon contact with any flesh.
Of course, this company’s establishment was prompted by the alarming statistics on the frequency of finger amputations due to the table saw.
The blade of the saw stops in less than five milliseconds, while its angular momentum quickly retracts the blade onto the table. Such a quick stop and retraction of the blade leads to minor injuries instead of serious injuries. Such a quick stop is occasioned by the difference in the capacitance and conductance between the flesh and wood.
How Does this Sawstop’s Automatic Blade Braking System Work?
A quick glance at the SawStop table saws will not tell you how different they are from the ordinary table saws, for they work just like the other table saws. Yet, the main difference lies in how quickly their blades stop when they come in contact with flesh. Let me explain the dynamics behind this automatic braking system.
Well, it works because the blade can pick up the electrical signals generated by your finger, which, in turn, triggers the brake cartridge located underneath. Once triggered, the brake cartridge springs upwards, then stops the saw almost instantaneously. The blades and cartridges of these saws, of course, are easy to replace.
The SawStop System can be subdivided into four basic phases, namely: monitor, detect, brake activation, and reset. The blade bears a low electrical signal which is continuously monitored by the safety system. Moreover, this electrical signal is generated by an oscillator.
This pulsed electrical signal is a 12-volt, 200kHz electrical signal. It is continuously applied to the blade side’s small plate. This pulsed electrical signal is conveyed to the blade using capacitive coupling.
On the other side, a plate picks up this signal and sends it to the threshold detector. Once there is contact with human skin or flesh, the threshold detector detects a below-the-threshold level of the signal. If there is a loss of signal of around 25 microseconds, the detector will immediately fire.
So, using a 10-inch blade, a tooth of that 10-inch blade will remain in contact with the skin for 100 microseconds. The detector will detect this contact with even one tooth contact of the flesh with the blade.
When the brake is activated, a spring pushes into the blade the aluminum block. This block is often held away by a wire from the blade. During the braking process, the wire melts instantly due to the electric current. Such a melting of wire is comparable to the blowing of a fuse. The four stages are as follows:
Stage 1 and 2: The Monitoring and Detecting
The first stage involves the blade carrying a pulsed electrical signal. Once the blade hits the skin, the signal is altered, considering that the human flesh is conductive. Such a change in the signal activates the blade’s safety system.
Stage 3: Brake Activation
The aluminum brake suddenly springs towards the spinning blade. It stops the blade from spinning in less than five milliseconds. The blade’s angular momentum prompts the blade to move underneath the table, preventing further contact of the skin with the blade. The power of the motor is also shut off afterward.
Stage 4: Resetting of the Saw
You can reset the saw afterward, and resetting is pretty easy. To do so, you need to replace the blade along with the brake cartridge to get your table saw operational again. It will take around five minutes to do the resetting.
Limitations of the Saw Stop
SawStop is very much aware of the limitations and restrictions of the design of their table saws. Some of these limitations are as follow:
- You must deactivate the braking system when working on wet and very green timber.
- You can’t use non-conductive blades with non-conductive teeth for this table saw.
- The braking system is engineered to work well with 3/32″ -3/16 kerfs. You will only limit the ability of the braking system if you use thicker or thinner kerfs. The braking is not practical to retrofit to your existing table saw.
- The activation of the braking system quickly damages the blade.
When operating SawStop table saws, you should not use gloves. Gloves can prevent the full functionality and benefits of this braking system. Nevertheless, SawStop table saws work in any environment, whether it is humid or not.
Table saws have been in use for more than 130 years; yet, it was only recently when the automatic braking system concept was incorporated into the system. Injuries from the use of table saws, of course, are grisly. Moreover, many of those who suffered injuries due to table saws are professional and experienced woodworkers.
None of them, however, thought that they would be injured using the table saws. This is because injuries due to table saws happen quickly due to momentary lapses of attention or judgment. Steve Gass, as the founder of SawStop, therefore, has done thousands of woodworkers a great service by conceiving of the flesh-sensing brake system for his company’s table saws.
Jason is a 40-year-old woodworker, carpenter and author who have been involved in the woodworking and woodcraft industry with 17 years of experience. He is expertise in technical aspects, woodcraft and furniture building projects.