Are Table Saws Safe Yet?

June 28, 2008 11:26 AM

A few years ago I saw a video where someone made a table saw technology where if the blade touches your skin it stops immediately and all you get is a knick on your finger. I was curious if this is being built into table saws yet? And if not why isn't it?

It would be top on my list of features when I buy one since anything that can cut off my hand scares me.

posted by GregX3 to technology (35 comments total)

You're referring to SawStop - it's available here, though it seems to be something particular to this brand of saw and not an industry-wide sort of thing (yet).
posted by jquinby at 11:32 AM on June 28, 2008

http://www.sawstop.com/

pretty expensive still I think, but if it saves a finger even once you'd probably be happy to have paid the cost.
posted by dan g. at 11:33 AM on June 28, 2008

I was curious if this is being built into table saws yet?

To my knowledge, it's still one brand only.

and if not why isn't it?

Fears of liability.

Here's a good NPR bit about it.
posted by longdaysjourney at 11:33 AM on June 28, 2008

and if not why isn't it?

I imagine large amounts of the mechanism are patented to prevent their gimmick and ensuing selling point being wider distributed.
posted by Brockles at 12:17 PM on June 28, 2008

The technology isn't new but none of the other manufacturers were willing to install it in their own saws. Something to do with liability if it doesn't work maybe? So they started to build their own saws. It's expensive because it's a high-end saw, appreciably larger and stronger than the portable types you get at Home Depot. But I think you'll find the cost is comparable to the equivalent Delta or Powermatic saw. Fine Woodworking had a review a few years back and it was rated highly.
posted by drmarcj at 12:21 PM on June 28, 2008

How does it know that the wood is something intended to be cut, and that the finger is not?
posted by Flunkie at 12:23 PM on June 28, 2008

How does it know that the wood is something intended to be cut, and that the finger is not?

The SawStop safety system includes an electronic detection system that detects when a person contacts the blade. The system induces an electrical signal onto the blade and then monitors that signal for changes. The human body has a relatively large inherent electrical capacitance and conductivity which cause the signal to drop when a person contacts the blade. Wood has a relatively small inherent capacitance and conductivity and does not cause the signal to drop.
posted by Optimus Chyme at 12:33 PM on June 28, 2008

Flunkie, your finger is a much better conductor than wood or other materials typically cut on a table saw. The technology passes a weak electrical signal through the blade. When the blade touches skin, the system detects a voltage drop and engages he brake.
posted by pmbuko at 12:33 PM on June 28, 2008

Awesome.
posted by Flunkie at 12:35 PM on June 28, 2008

I think I saw a demo of the SawStop at one point where they used a raw hotdog to show that flesh would not be damaged when coming into contact with a spinning blade.

Do hotdogs also have a relatively large inherent electrical capacitance and conductivity which cause the signal to drop?

I mean, seriously? I have a ballgame Monday and this is "eating me up."
posted by Exchequer at 12:45 PM on June 28, 2008

Sawstop vs hotdog
posted by zippy at 12:50 PM on June 28, 2008

The electrical signal they are trying to detect is very tiny in order to distinguish between wood and flesh in an inherently noisy electrical environment. The detector would have to be finely tuned to not generate false negatives or false positives. A false negative means you have an injury. A false positive means you are out an $80 single-use brake cartridge and a new saw or dado blade. If it works as advertised it seems like a worthy product, but I would want to see some independent test results.
posted by JackFlash at 12:59 PM on June 28, 2008

From that demo it seems like you'd have to replace the brake, but even so I'd rather be able to cut my hot dogs into bite size pieces.
posted by Gungho at 1:02 PM on June 28, 2008

JackFlash, I work for the company that provided the hardware and software for the prototype of the Sawstop. They showed the prototype at our big annual conference a year or two ago. The video is a bit marketing-heavy, but it shows the system in a bit more depth. About halfway through the video, you can see the actual amplitude of the signal on the blade and how much it changes when it's touched by a human (or hot dog).
posted by cebailey at 1:32 PM on June 28, 2008

If I recall correctly from the articles when this first came out, each time it puts on the brakes, expensive parts need to be replaced to make the saw go again.
posted by winston at 1:49 PM on June 28, 2008

winston is correct. As I understand it, the sawstop works by firing a bolt into the blade when it detects skin contact. That bolt is a one-shot item, so you need to replace it when it gets triggered.

Sawstop also tried to get legislation passed that would basically make something like their technology a mandatory part of any bench saw. That failed.
posted by adamrice at 1:54 PM on June 28, 2008

As I said above, the single-use brake cartridge is $80 and it also destroys the blade so that has to be replaced as well. That is well worth saving a finger, but I would still like to see real world independent test results, particularly regarding false positives and negatives. I have designed capacitive sensor systems and the DSP software is looking for a particular electrical signature. It is not a trivial task. The question is how well it can do that in a very noisy electrical environment.
posted by JackFlash at 2:04 PM on June 28, 2008 [1 favorite has favorites]

The concern of the other manufacturers was exactly as drmarcj describes. "If we install this and it fails to go off when it should, wouldn't our liability go up?"

The Saw Stop people realized they would never be competitive price wise with the saws that didn't have it, and so they set out to make the best table saw they could. Their cabinet saw is on par with the Delta Unisaw, which is kind of the gold standard of table saws. They also put some other safety features on their saw, like a riving knife and a better guard than what you get with a Unisaw. At my local Woodcraft they carry these and have a spent blade/brake sitting on top their demo model. They're pretty much fused together.

All that being said, while the big whirrrrry table saw blade can cut you, it also can take whatever you're working on and throw it at you at an appreciable fraction of the speed of sound, brake or no. So, even if you do get a saw like this, get a good book or something and make sure you know what you're doing.
posted by Kid Charlemagne at 2:07 PM on June 28, 2008 [1 favorite has favorites]

The book I'm reading right now " A Splintered History of Wood" has a bit about it. According to the book, the inventor tried it on himself.

I'm more of a handtools guy, but the cost of the replacement blade is still going to be less than the cost of the hospital trip unless if you have truly astounding insurance.
posted by drezdn at 2:49 PM on June 28, 2008

The electrical signal they are trying to detect is very tiny

Tiny signals are easy to detect. Have you ever used a laptop touchpad? That relies on a very tiny signal, but it works perfectly reliably. If you try using the touchpad with a piece of wood, it won't work. SawStop works the same way, but probably uses better parts than your $1 touchpad.
posted by jrockway at 2:58 PM on June 28, 2008

Yes and it is awesome. Only thing is that everytime it goes off you have to buy a new blade. Veeeeeeery expensive. The scene shop I used to work in had one, and when we bought it the rep came and showed us with a hotdog.
posted by thebrokenmuse at 3:06 PM on June 28, 2008

I believe it's the same principle that makes iPod click wheels and iPhone touch screens work. So I guess you could operate your iPod touch with a hot dog stylus, if you were so inclined. It would leave some pretty nasty prints, though...
posted by Rhaomi at 3:10 PM on June 28, 2008 [1 favorite has favorites]

"liability concerns — and… Gass’ request for an eight percent royalty on each mechanism".

I gather Gass didn't approach the manufacturers in a particularly friendly way, and when they didn't run with his idea, he tried to make his technology mandatory.
posted by zamboni at 6:02 PM on June 28, 2008

I'm writing this from a wood shop that has two SawStops. I've been around once when the brake fired--someone was pulling her hand back after a cut and didn't notice the blade was still turning. It was loud and scary, but she was just fine. I think they gave her a band-aid, she bought a new brake and blade for the saw, and that was it.
posted by jewzilla at 6:05 PM on June 28, 2008

I used to do a little safety and you'd be amazed at what some idiots will do. My concern, if I worked for the company that made them, would be that it would get fired and need replacements, and some idiot would figure out a way to bypass the mechanism, change the blade, and "get this job back on the road". The first rule of safety is, you never run out of idiots.
posted by unrepentanthippie at 6:34 PM on June 28, 2008

This would be a great technology to put in wood chippers.
posted by greenknightwatch at 8:53 PM on June 28, 2008

a friend of mine (who has been making her own kitchen cabinetry) has one of these saws. at it has not been triggered due to accident yet.

there is a plan, at some as yet unspecified point in time, to spent the bucks for a replacement cartridge and trigger it on purpose. there will be video. oh yes, there will be video of this event.
posted by rmd1023 at 9:27 PM on June 28, 2008

Previously... (maybe where you saw the videos).
posted by borkencode at 9:51 PM on June 28, 2008

What I remember reading is what JackFlash wrote about. Lots of false positives equals lots of downtime and cost. Each replacement is like 100 dollars. What if you get 5 false positives today?

I also think the liability argument is bunk. We wouldnt have seatbelts and airbags if it was true.

I think if you want this tech you need a patent-free implementation and congress to mandate it. The current approach doesnt seem like a way to get this done.
posted by damn dirty ape at 9:52 PM on June 28, 2008

Quite apart from the technical issues is this basic conundrum.

Table saws, when used correctly, are generally safe.

Expensive table saws are purchased by people with enough investment (as a profession or a hobby) that they take safety seriously already.

Cheap table saws, on the other hand ....

This is an argument that could also be applied to many other safety devices, of course, but in general I think most people do a sort of Fight Club risk assessment and decide that it's too much to spend on something they view as a relatively tiny risk.
posted by dhartung at 12:29 AM on June 29, 2008

Table saws, when used correctly, are generally safe.

Expensive table saws are purchased by people with enough investment (as a profession or a hobby) that they take safety seriously already.

Cheap table saws, on the other hand ....

During the brief time I worked as a professional carpenter I met three guys who had cut off some piece of a finger/thumb at one point or another. They were using expensive table saws. I don't know if hard data exists on the subject, but I would think that professionals are probably a large percentage of table saw injuries. They use them a ton more than hobbyists with cheap saws and they use them when tired, hung over, etc. Not to mention that they are more likely to defeat the safeties on a regular basis.
posted by Lame_username at 5:26 AM on June 29, 2008

The shop I work in has one of these installed, and I've spoken to many other folks who have them. In the field, the false-positive rate (brake firing for "no reason") seems to be kind of high, and I've never heard of a false-negative. Obviously, if false positives are the price you pay for not losing a finger, nobody's complaining.

Part of installing any tool is making sure you have a budget to keep it maintained; SawStops just come with an N * $80 yearly no-lost-fingers charge. It's not a bad deal, especially if you're running a shop that has novice users on table saws. (Though I'll also say that the scariest table saw accidents I've ever seen have always been at the hands of multi-decade veterans who assumed a little too quickly that they knew what was going to happen.)

False positives look for the most part to be the result of materials choice -- if what you're cutting isn't wood-like enough (say it's got some paint that turns out to be a little conductive, or it's chip- or particle-board with the wrong filler) it can act like enough of a capacitor to trigger the firing mechanism.

As I understand it (though I may be wrong here), it's marginally safer to put your finger in the front of the blade (as in a feed accident) than hit from the back (as jewzilla described) because part of the braking mechanism uses the angular momentum of the blade to drive it forward and down into the table -- it's heartening to hear that coming at the blade from the other side only needed a band-aid too.
posted by range at 7:55 AM on June 29, 2008

I saw this on Engadget/Gizmodo/Digg (don't remember which -__-) a couple of months back. According to the comments on the post, it's not widely released because of liability. If you cut your finger on a regular table saw, it's your fault. If you manage to lose your finger on that safe table saw, it didn't do their job properly.

Or something along those lines.
posted by carpyful at 6:08 AM on June 30, 2008

a table saw is only as safe as the operator. the Saw Stop will certainly prevent some injuries. however, a kickback injury can be severe and the blade has no contact with skin. a kickback happens when the spinning blade catches the wood and throws it back at the operator at light speed. kickbacks can be prevented by using basic safety procedures and splitters or riving knives. see video of a kickback here.

experience has no bearing on injury rate. one moment of carelessness, no matter how long you've been woodworking, can result in an accident and/or injury.
posted by killy willy at 11:09 AM on July 1, 2008

regarding the Saw Stop technology: the man who developed it shopped it around to all the big manufacturers. however, he also wanted an inordinately large piece of the pie for this wonderful technology. since nobody would agree to his terms, he developed his own saw. now he's lobbying to make his technology mandatory in all saws. not sure how that's going, though.
posted by killy willy at 11:12 AM on July 1, 2008