Article on Skin sensing table saw

Here’s a link to an interesting article about the skin sensing table saw that prevents many saw related injuries. The function is quite interesting. I can see this technology being added to many many types of machine tools to improve workshop safety substantially.

Wow, if that isn’t one of the most interesting and practical inventions of our time! As a young kid I can remember meeting the man who helped build my parent’s house, who only had 7 fingers! This could, and should, revolutionize the business.

However, upon reading that article, I find it fascinating how the real-world market actually works. Clearly, this device has the potential to save not just fingers, but lives in the right applications; Chainsaws, hedge trimmers, lawn movers, you name it… But the manufacturers are reluctant to include it because of liability, or more importantly, their present lack of liability. Hopefully, the one law change will force manufacturers to include this technology (or similar ones) into their products.

Sawstop LLC doesn’t seem to be a publicly traded company. But, if they were, I’d make sure I had some money to invest in them. It looks to be a great company, who’s trying to do the right thing. Compare that to the pipeline debacle that BP is in right now… (sorry, let’s please keep this thread to a discussion on Sawstop, thank!)


The article is interesting, and from an engineering perspective very disturbing.

If I understand it correctly, the inventor is a patent attorney with a long term hobby/interest in wood working. He decided to invent a way to stop powerfull table saws from cutting off fingers.

As an engineer, here is my problem. The inventor was not in the power tool industry. He uses power tools for his woodworking, but he is not a power tool designer.

He thought he had invented something that everyone would want, but was rejected by every company he approached.

So what did he do (here is the disturbing part): he managed to start a process to enact laws and regulations to force companys to use his invention (or something like it). This is just wrong! His ‘engineering’ attempt failed to get his design into production, so he turned to his lawyer friends to cram it down the industrys throat.

He has followed what engineers call the two step design cycle: Here is a problem and here is the solution. That is the human intuitive approach to solving problems, but engineers have learned over the last couple hundred years that this is not the way to do things.

If fingers getting cut off is the problem, then people who are involved in power tool design step back and study the whole problem, the whole system, the entire woodworking process, to see what leads a person to push their fingers into a saw blade.

Making a saw that will sense fingers may not be the best answer (the power tool companies seem to agree, or they would have jumped at the chance to buy his patent).

The power tool industry, however, has a very different view of the subject. Representatives cite a plethora of technical problems with SawStop technology, including too many “false positives” or “nuisance trips,” cost of replacement cartridges after the brake fires, and difficulties cutting conductive materials, such as moist wood. Moreover, they say, Gass is asking for an 8 percent royalty on each saw sold, a figure they describe as ridiculous.

From my own experience with industrial accidents, many are caused by operators disabling the safe guards, over riding them, and then getting hurt. This system would be no different - if someone wants to bypass it, because it keeps stopping the saw for false positives, then it will be no different than other safety systems already in production.

Whats more, if people get the idea into their head that their saw will not cut them, they will get more careless, which will result in more injuries.

If someone takes a coat hanger and wires the guard on a saw blade up, its obvious to anyone that the guard is no longer over the blade. But if someone disables this stop-saw system, by cutting a wire or jumpering a sensor, another user walking up to the system will have no indication the system has been disabled.

the idea that engineers in the power tool industry care more about law suits than user safety is absurd, and down right insulting. If your invention is a good idea you dont need a plane full of lawyers to force people to implement.

How’s this going to work if you’re cutting metal?

Ken, I would almost agree with you. However, the power tool industry hasn’t taken that step backwards to address the problem. Since they are NOT liable for people cutting their fingers off, they are NOT spending the money to solve the problem.

In the industrial world, yes, workers do bypass the existing safety systems and injure themselves. And I would assume that the push for these safety devices came from the liable companies and their insurance holders. But how many home woodworkers have safety systems similar to this? What is the percentage of injuries due to job-related vs. personal accidents? I don’t know, but I can bet that the wife of the home woodworker would shell out the extra cash to have a device like this at home.

And finally, let’s not forget that it’s not the engineers that develop the requirements for a product. It’s the sales/marketing team, along with a lot of input from those lawyers again. Bottom line, it comes down to money and liability…


Poorly. :stuck_out_tongue:

If you’re wearing gloves, and with proper attention to the design of the table surface, it might work. But who cuts metal on a table saw?

It’s people in the power tool industry who pointed out the liability aspects if this invention were to be widely adopted. They’re not engineers, they’re “liability experts”. You can dismiss their idea as absurd if you want, but the explanation seems entirely plausible to me.

Whether or not a flesh-sensing saw blade is the “best” answer is not important. The problem at the moment is that table saw manufacturers are not obviously taking any steps to advance the technology of user safety. SawStop has a proven technology. The only compelling reason the manufacturers give for not licensing it is economic, and I don’t blame them for balking at an 8% royalty demand.

I dont know how proven it is. I found it interesting that they did a hot dog demonstation at a trade show at 30 minute intervals, and there was mention of a replaceable ‘brake cartridge’ in the system. Was there some significant cost, or down time involved, so that they only did a demo once every 30 minutes at a trade show?

I dont know the specifics of how it works, but I do know that basement inventors often design systems in a way that they work ‘once’, and they dont really care what it takes to get it to work again.

Do you have to replace some nail-gun-like brake cartridge every time the thing stops the blade? What is the down time after it triggers?

If Im sawing wood at 5pm on sunday afternoon, and it triggers on a damp piece of pressure treated wood, am I shut down till Sears or Home Depot opens the next morning?

If so, guess what Im going to do to my table saw?

I got a portable MPG4 video recorder and player about a year ago, that wont let you record a DVD if its copy protected. So you buy a DVD, and you want to copy it into your MPG4 player to watch it later on a trip, and you cant.

It took me about 30 seconds on Google to find out how to over-ride the copy protection system (you let the player record for 10 seconds with the input unplugged, after that it will record anything).

This will be the same deal. If someone wants to over ride it, they will. (esp after the 7th time it goes off on a damp piece of wood).

How many consumers want to pay the extra cost for implementation of a system like this? Before using any tool you should understand the proper operation of that tool, which includes proper safety precautions. If I cut my finger off using a power tool I suspect I will be at fault for ignoring and/or shortcutting safety procedures (guards around cutters/blades, push sticks, feather boards, anti-kickback devices … etc …).

How does that joke go ??
What is the difference between a Lawyer and a Catfish ? :stuck_out_tongue:

The article mentions a fuse that gets burned up to spring the brake. I believe that this is what needs to be replaced. A task like that wouldn’t be much different than an ordinary replacement fuse on a consumer product.

If you download the user manual, it goes into great detail about replacement of the brake system.

First, you have to understand how the brake works, then you can understand why it’s a bit more complicated that just replacing a fuse or resetting a spring. The brake is basically a piece of aluminum that is forced into the teeth of the blade. When the system senses a step change in the control voltage, this curved aluminum block gets rammed into the blade. The blade embeds itself into the block and is stopped in a few milliseconds. (The slo-mo video is wild to watch…)

So, what needs to get changed? The entire brake system, which looks to be one complete module. However, since the blade is being forced into the aluminum, they recommend changing out the blade as well! So, can the blade and module be changed out in 5-10 minutes? Probably. The toughest part is probably extracting the blade from the aluminum block, nothing a block of wood and a hammer can’t take care of.

So, is the extra money and the time delay worth a finger? That’s up to you. Would I recommend a product like this in every school system that has a woodshop? You better believe it! A trained woodworker should have the experience and the know-how to protect himself. Unfortunately, I can’t say that about most students, or even myself.


You reminded me of why I posted this originally. It immediatly made me think of your former Hydrogen Source coworker who cut off 3 fingers on his table saw (all reattached). Also the number of people around our shop who are missing part or all of a finger. To me adding the price of the device up front and replacement parts is worth it no matter how careful you think you are. If the device is retro-fittable to older saws I’ll be buying one for my father, an avid wood worker, asap. Otherwise he may have to wait a little longer until we get him a new saw.


Give me an hour and I’ll bet I can come up with 5 ways to design a table saw type of machine that will prevent you from pushing your fingers into the spinning blade, and none of them will involve destroying the blade or jamming blocks of alumimun into spinning machine parts.

Dean Kames once said something along the lines of “Every engineering project is a solution to a problem, but not every engineering solution is something the public needs.”

I believe this invention is a marvelous idea, but it just isn’t practical in the real world. Once you (a company) start claiming things to be safe, all it takes is one equipment malfunction and you’re really in trouble.

The problem I have with things like this is that the easier you make it for people to do something, the lesser skilled they become. I think technology like this would put power tools in the hands of people who really have no business using tools. Power tools are nto for everyone, there’s no changing that fact.

I mean seriously, what are they going to do, safen every dangerous tool out there? Put a compressable sleeve over dril bits? Permanently affix a shield into a welder’s head? Make an oxy-acetylene torch that you can’t point at yourself?

No invention should ever replace simple diligence when it comes to using power tools.

A little research shows more than 50 people in the past two years who have had their digits saved, and none who have lost a finger, while using a SawStop table saw.

The manufacturers’ complaint about false triggers on wet wood sounds like classic FUD. I know first-hand that a simple capacitive detector is discriminating enough by itself to tell the difference between flesh and damp plywood, and the system is additionally looking for a specific signature that indicates the blade’s teeth are suddenly encountering a conductive object. You’d probably have to try cutting something like brine-soaked pine in order to force it into going off. According to the company, the system will trip if you feed it wood with greater than 40% internal moisture content – which is something nobody should be doing. If you need to abuse the saw like that, the SawStop products have a temporary override feature that disables the brake actuator, but leaves the sensor and an indicator panel active so you can see if it would have triggered the brake on a given cut.

As for the proposal that you can prevent people from touching the blade, the same argument about subverting safety features applies. The SawStop technology is supposed to keep contact with the blade from doing major damage to a person when the usual safety procedures and equipment fail to work perfectly, whether by accident or intent. It’s like an automobile’s air bag, or a ground fault detecting circuit breaker.

But I don’t think that argument should be used to naysay a safety feature. If a power tool can be made more benign when simple diligence is trumped by accidental circumstance, I consider it a good thing.

The point of inventions like this is to make systems more fail-safe. That means they’re more safe when existing practices fail – which they obviously do.

First-hand? I hope you still have both hands intact!

This reminds me of a classic lampoon book titled Fixit And Be Damned by Lawrence Lariar (Prentice-Hall, 1955). It contains numerous how-not-to cartoons, including one showing a guy who has just severed his hands while using a table saw. Above the saw there is a sign reading “Hands Off!”

I found the SawStop claim of “52 saves” interesting. Apparently, SawStop customers report incidents in which they were saved from injury. Other table saw users just report the injuries.

SawStop has a built in measure since the satisfied customers have to order a replacement for each incident. The customers without hands probably have trouble placing any orders and can’t be counted.:rolleyes:


First-hand? I hope you still have both hands intact![/quote]

I built a touch-sensing light switch about thirty years ago, using a 60 Hz probe signal (instead of the much more sensitive high-frequency signal employed by SawStop). My sisters and I had fun trying to see just what would trigger it. Keys, coins, and coat hangers did. Wet wood did not. Pencil lead was hit or miss.

I had a TV set with a touch sensor channel selector.

Every once in a while a fly would walk across the buttons, and change the channels. I guess the fly didn’t like my choice in programming.

As hard as it may be to accept, it is not possible to design power tools and powerful equipment that nobody can get hurt on (by accident). How many injuries per year are acceptable? Zero if you are the person who lost body parts.

But the reality of our lives is that we control powerful machines everyday, for some people its all day long. If you take a zero-accident approach then everything has to be very expensive, time consuming to use, with double redundant safety features. ( the ultimate system would be fully automated, you have a stack of boards and the machine saws them for you, with no human intervention - you stand outside the perimeter guards and push the start button).

Even then, if you stop a person from sawing off his fingers they may very well step in front of a bus an hour later, choke on a hot dog, fall down the stairs, get struck by lightning, or hit by a marble size meteorite (or all of the above at the same time :ahh: )

I know there is a balance to be struck. To me it seems more reasonable to find ways to keep fingers away from saw blades, than to design saw blade/finger contact systems that jam blocks of aluminum into spinning blades.

We have to accept that emergency rooms will not be put out of business anytime in our foreseeable future. We should do everything reasonable to keep people safe from harm

but everything about this system looks wrong to me. Esp the fact that it is being mandated by lawyers and elected officials, not by people who work in the industry to ensure worker safety.