Skin Sensing Table Saw

killabrew writes "Check out this article from Design News about a new skin sensing table saw technology that is on the verge of becoming a mandatory piece of hardware on every table saw. For years inventor Stephen Gass persevered in the face of legal, corporate and technical foes, he is forcing society to rethink its acceptance of saw blade accidents."

Comments

Good product

[dave-tx]

Here is a writeup of the saw's debut at the International Woodworking Machinery & Furniture Supply Fair (2000). I remember reading this back in 2000 thinking "great idea, but I wonder if it'll ever get adopted". Glad to see it's gaining traction - the table saw is the only piece of equipment in my shop that I'm nervous around.

Now if they can solve kick-back, I'll be a tablesaw fiend.

Re:Good product

[Anonymous Coward]

They have solved the kickback problem. First, this saw uses a riving knife at the back of the blade. That is, it has a rather sturdy curved blade that stays fixed behind the rotating blade. The riving knife goes up and down with the blade and helps keep the wood from touching the back of the spinning blade, which is the root cause of kickback. Another think you can already do to reduce kickback is to ensure that you fence is exactly parallel to the spinning blade. In the alternative, you can have the back of the fence a few thousandths of an inch further out from the blade than the front. This keeps the wood from getting pinched between the fence and the back of the spinning blade.

For those that are curious (I can't get the article to come up, perhaps the server is melting) the SawStop works by sensing a change in the electical resistance in the blade when it touches flesh. (Since wood is, generally, of low moisture content, it will not set off the mechanism.) When the flesh is sensed, a heavy spring launches a sacrificial aluminum block into the blade and another spring retracts the entire mechanism. The aluminum block and your $50 to $120 blade must be replaced.

-cliff

always two sides to every story

[Anonymous Coward]

As someone who was involved in evaluating this technology for a major US manufacturer of power tools, there are a number of issues which prevented early adoption. First and foremost was the inventor's demands for unreasonable royalties (including a percentage of the gross sales of table saws from preceding years!). I heard the director of the power tools group say that if the royalty had been reduced by 50%, it would have been a no-brainer. As it was, the proposed royalty structure was just unsupportable for a saw that sold for $500.

The second issue was that the product had great difficulty distinguishing the change in capacitance due to human flesh from that due to very wet lumber. This has undoubtedly been improved over the past few years, but people would have been somewhat unhappy to have false triggers that required them to a) replace the safety cartridge and b) their saw blade, which is consumed when the system triggers. Not to mention having the bejeesus scared out them when the system fires in error.

To talk about the inventor persevering in the face of corporate pressure is silly. This isn't a David vs. Goliath story. The inventor was a patent attorney that tried to bludgeon power tool companies with a 250+ page patent, and he could have sold his concept on day one if he hadn't been quite as greedy. There was no shortage of companies looking for competitive advantage in the power tool industry, which has been pretty stagnant of late.

This has been around for years

[RembrandtX]

Its been around for years, and has been shopped to the major power tool manufacturs [one of the largest, I used to work for, so i'm not talking out of my butt here.]

All of them turned it down due to legal implications, as well as adding to the cost per unit price.

Leagally, if a power tool manufacturer added this to their existing line of table saws, it *COULD* be taken as an admission of guilt that their previous models were not safe, any accident cases (no matter how stupid) would then have another chance at a successful suit.

Also, the inventor has been lobbying for *YEARS* to get his invention as a required component of table saws. He hasn't even had success in California - the most liberal state for passing stuff like this - let alone elsewhere.

I'm not knocking his invention, I've seen it pitched first hand .. the guy whipped a raw hot dog at the blade as fast as he could, and there was only maybe 1-2mm of damage to the hotdog before the blade dropped down into the brakes.

Destroying the blade of course. which .. at $50+ a pop .. kinda hurts.

Another reason this hasn't been adopted yet is that pressure treated wood also tends to cause the brakes to fire off ..

This has been out for *years*.

[Chirs]

For the non-woodworkers in the audience, this tech has been available for several years, and information on it was available for at least a year before the saw itself.

The "Sawstop" modifies the electrical potential of the blade, and can thus detect when skin hits the blade. Of course it also triggers if you cut metal, so it has a disable switch. Apparently wet wood doesn't trigger it.

When it detects flesh, it has an explosive charge that rams a chunk of aluminum into the blade stopping it within ~3ms. I saw it demoed in person at a wood show. The demonstrator slid a hot dog into the blade at a fair speed and there was a large bang. The hot dog had been cut into maybe 1/32" or so (a bit under a millimetre).

The main problem is that the inventor wanted huge royalties from existing tool companies, and tried to force through legislation making it mandatory to include the device on *all* table saws in the US. As you can imagine, people were less than impressed about having it rammed down their throats. Even now, the saw that incorporates this is a very nice saw, but they still charge about 30% more than for other comparable saws.

Re:This has been around for years

[jsupreston]

Not only that, but if for some reason the device acidentally trips, you're out a whole lot of cash replacing the blade, brake shoe and no telling what else. For someone who can afford a $2000 cabinet saw, this may not be that large of an expense, but for the average person doing this as a hobby, we tend to pinch every penny. Heck, I've been doing this as a hobby going on 10 years, and I can't justify to SWMBO why I need a dado stack for my saw. If I had to buy a new saw with this technology, I'd have to give it up, given the cost of the saw and repairs. Plus, a little common sense would almost reduce the need for this completely. Use a push stick when ripping narrow stock. Use feather boards where appropriate. Use a miter sled when cross cutting. If possible, leave the blade guard on (not easy...my previous saw was safer without the guard due to a crappy splitter on the guard). If you have to, paint a red line in front of the blade on the saw table showing where the blade is. Paint a perpendicular one showing where the throat plate starts. Don't stand in front of the blade if you don't have to. And, if you don't think it is safe to do the operation, then DON'T DO IT. And yes, before I am asked, I've not followed all the rules myself. I did get a very bad scare about 3 years ago. I was cross cutting something, and felt a really strange vibration on the tip of a finger. I looked, and somehow I had gotten the tip of a finger past the teeth on the blade, and my fingertip was resting on the side of the blade while spinning. Fortunately for me, I was not injured, and since then I have tried my best to make sure that I never have that situation again. I have found a great resource for all sorts of shop info, including safety. BT3Central.com has several forums. The forum was created for owners of the Ryobi BT3x00 saws, but anyone is welcome. I have gotten lots of advice and inspiration from there. We all pretty much agree that the idea behind the sawstop is a good idea, but not that practical given its cost. Like I mentioned earlier, most of us would have to give up our hobby if we had to buy one.

Re:Whats the problem?

[johnny cashed]

In the US a safety that could be disabled by wedging cardboard in it wouldn't get past OSHA. They have thought of that and require the buttons to cycle, so you cannot just wedge it. I believe that in Europe, light curtains are also used. They are used in the US too, but not by themselves, because OSHA has very high standards for a light curtain system.

This is a good summary of the issues: http://www.seton.com/seton/internalHtmlAction.do?r elpath=/pages/content/en_US/setonalerts/articles/0 904/0904_mach_safeguard.jsp

Re:"Saw III"

[Skreems]

I've actually seen a demonstration where the president of the company used his own hand. Quite a show of faith in your product, I have to say, and very impressive as a selling tool.

re: cutting frozen meat

[maddogsparky]

My dad once butchered an animal (beef, I think) and left in the barn to cool. He couldn't get to it for a few days and it froze solid (Minnesota winter). He needed to cut it into smaller chunks to be able to carry it inside for cutting up. So he thinks: chainsaw!

Much of it had to be thrown out due to all the bone chips. :-(

Safety aside.....

[Sergeant Beavis]

Its actually a pretty damn good saw. I've used the SawStop cabinet saw at a couple of demos and I've been impressed with it. Losing a digit is always a concern, but anyone with a healthy respect for their tools will come away with fingers intact. Kickback is a much more dangerous situation because it can happen even when you are being careful. The SawStop has a self adjusting Riving Knife that prevents wood from binding against the rear of the blade and thus being thrown back at the end user. I've been into woodworking since I was 5. I've gone to many church and house rasing to help others and still volunteer my skills to Habitat for Humanity. In that time, I've been fortunate to keep my digits, but I've experienced the pain of kickback once. I was lucky to have gotten away with just a bruise. Kickback can flat out kill a person. Riving knives are very common on European built table saws, but are rare in the American market. We usually get a splitter with kick back cawls that should catch the wood as it gets kicked back. Normally it works well but a Riving knife prevents kickback in the first place. I can't think of one other US manufacturer that offers it on a cabinet or contractor saw. Saw Stop includes it on all of their saws.

Outside of those items, the SawStop is also very well balanced, it has almost no vibration, even less that most other Cabinet Saws. The trunions are solid and move the blade into position with little effort from the user. It also has a magnetic cutoff switch positioned right above the users knee for quick shutdown. It also includes a Biesemeyer style fence. Its only real drawback is that it is very expensive at $2800 for the basic saw. Options can run well over $5000. While I still like it, that money could be better spent on a European Combination Machine such as the Laguna or a Delta Unisaw with alot of money left over for other tools.