Licensed Professional Engineers
FORENSIC CLUES # 23 - "Advances in Table Saw Safeguarding - Saw Stop " by John L. Ryan and L.D. Ryan
A newsletter dedicated to keeping attorneys informed of the technical side of product liability cases.
Volume 23 April/May 2007
“Advances in Table Saw Safeguarding—Saw Stop”
By John L. Ryan
Table saw accidents occur frequently, often resulting in serious accidents when the operator comes in contact with the saw blade. The difficulties in guarding table saw blades with conventional guarding techniques often leads to ineffective guards that are removed by saw operators due to their lack of function and flexibility.
Saw Stop LLC is a company that produces the most innovative table saw on the market. Saw Stop produces complete table saw machines, which incorporate their ingenious saw stop technology. These saws are designed to detect when a saw blade comes in contact with skin, and stop the saw blade within 1/200 th of a second. The manufacturer acknowledges the fact that table saw users often remove the manufacture supplied guards. They adopted a different approach to the design problem of guarding table saws, minimize the injuries when contact with the blade does occur.
The blade not only is stopped within 5 milliseconds, the blade is retracted down into the saw body, also helping to prevent further injury. This design relies on the occurrence of an accident, contact with skin, to initiate the braking sequence. The design uses a sensor that monitors a voltage signal that is supplied to the saw blade.
The electrical resistance values of human tissue and wood are vastly different, so the sensor can detect when the saw blade is in contact with wood, and allow normal saw operation, or in contact with flesh, and initiate the quick-acting blade brake. This means that a person who comes in contact with the point of operation on a Saw Stop table saw will be injured, but the injury will be a minor laceration instead of a serious laceration, amputation, or worse.
This saw also has other safety features to help prevent the necessitation of the blade brake. The Saw Stop saws include an anti-kickback device that conforms to the blade shape on the back side of the blade. This device is a European style ‘riving knife’ that Saw Stop claims minimizes kick backs. Riving knives have the same goal of splitters – to keep the kerf from closing on the saw blade. The kerf is the slot that is cut into the board with a saw. If the kerf closes due to various forces acting on the board, some of them created by the sawing and feeding of boards, the board can get caught by the saw teeth and propel the board towards the operator. The riving knife doesn’t need to be removed like a splitter when performing non- through cuts since it doesn’t extend above the blade. The shape of the riving knife allows it to be placed much closer to the blade than traditional splitters.
Saw Stop’s Riving Knife
The Saw Stop table saws offer a new level of safeguarding for saw users. The manufacturers have built the safeguard into the design. The blade brake is a safeguard that cannot be removed, although there is a bypass switch built into the saw that is to be used in wet conditions. Wet conditions could trigger a false blade brake, in which case the blade braking system can be overridden temporarily. While this does give the operator an opportunity to bypass the safety system, the operator will have little motivation to bypass the Saw Stop blade brake. The Saw Stop does not interfere with normal operation in most situations. The Saw Stop blade brake does not interfere with seeing the cutting point or feeding the material like traditional table saw guards can.
The safety feature of the Saw Stop can be used for dado cuts, although a different brake cartridge must be installed for dado cuts. This cartridge is easily and quickly replaced.
Saw Stop’s website has a section dedicated to testimonials from customers who have had the misfortune to test out the Saw Stop’s safety feature. Numerous examples are shown on the website of customers who for various reasons contacted the saw blade. These testimonials often include photographs of the table saw and of the operator, directly after the incident. Just as proclaimed and designed, the operators had small lacerations only, with no lost digits or worse injuries. Check this out for yourself at:
Implications of the Saw Stop
The Saw Stop will likely have a large impact on product liability cases involving table saws. Often state or federal laws require plaintiffs to show a solution to a hazard in a product. These solutions are sometimes patents showing technology that could have prevented a particular accident, sometimes it is alternate designs created by engineers that are based on engineering principles. Table saw lawsuits often involve accidents where the saw operator is cut by the spinning saw blade. Table saw guards that are included with most modern table saws are inadequate in many aspects, and must be removed for certain woodworking cuts and techniques. Saw operators remove guards to be able to perform these cuts, and sometimes operators will remove the guard for better visibility. Various solutions exist on the market, including the Brett-Guard, an innovative guarding solution that greatly improves traditional table saw guards. The Saw Stop is a very effective safeguarding technique that could prevent many table saw accidents occurring every day. The Saw Stop can be shown to be an alternate safeguarding technique that is in production and is proven to prevent severe accidents. This may impact table saw litigation, and hopefully, table saw manufacturers will take note and develop safeguarding techniques that will be as effective as the Saw Stop.
See Donegal Bay Publishing’s Saw Manual for more information at:
which contains in-depth investigations of saw designs, industry standards, state of the art, human factors, and other information.
www.donegalbaypublishing.com—Product Liability Manuals
Got a saw accident or other product liability case? Check out our defective product information at www.donegalbaypublishing.com where you can see excerpts from our manuals. Order the new edition of The Power Saw Manual—A Product Liability Manual by calling (479) 549-4860 or go to
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