SawStop Injury

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patlaw

Mike
Corporate Member
This video is hopefully one of the worst injuries received with a SawStop. Don't watch if you're queasy.

[video=youtube;1wJQn_UGAKY]https://www.youtube.com/watch?v=1wJQn_UGAKY[/video]
 

patlaw

Mike
Corporate Member
all I see is a black rectangle in your post----------no play button, no link, etc. ?????
Can't help you with that. Maybe Ethan has an idea. It's working for others, including me. Here's what we see:
attachment.php
 

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KenOfCary

Ken
Staff member
Corporate Member
I have the overarm blade guard and the dust collection it adds is very good. Recommended.
 

Phil S

Phil Soper
Staff member
Corporate Member
Obviously that injury could have been much worse. But my question is did that sawstop function correctly or did it fire slower than it should have. I have seen the demo many times but never seen the hot dog look like that. I wonder if sawstop owners can test their saws response time without destroying a brake and blade
 

patlaw

Mike
Corporate Member
Phil, as I recall, his saw is seven years old. I wonder if the newer ones are faster. I had the same question.
 

Grimmy2016

Administrator
Scott
I would say that this mans being out $300 is a lot better deal than losing the whole thumb and potentially eliminating his ability to even do woodworking. Its pretty hard to grasp things without a thumb I would imagine.

Just saying... he is a lucky man and I would say the SawStop saved him a lot more than what he lost in cash.
 

JimD

Jim
Senior User
I've watched some demos with hotdogs and I suspect the guy in the video was moving his hand faster than the hot dogs are being moved into the blade. He describes moving material away form the blade and if he does it like I sometimes do it, he was flicking it away with a quick movement. I think how many teeth get you and how deep they get you are a function of how your hand is moving. More forceful movement towards the blade and quicker movement both mean more injury - even when the blade stops in the same time. I have no idea if SawStop has changed their cartridges over time. They are using something like gunpowder to trigger the blade dropping and the aluminum block jamming into the blade but there are different kinds of gunpowder that vary by burning rate - there is actually quite a large range. (something like a 25ACP needs a lot faster powder than a 375 H&H rifle).

To me the lesson is that a SawStop is not a reason to adopt bad practices at the table saw. You still can get bit.
 

tri4sale

Daniel
Corporate Member
Phil, as I recall, his saw is seven years old. I wonder if the newer ones are faster. I had the same question.

I've wondered if the cartridges wear out over time, and if too old don't function as well or as fast. A lot of shops have wide variations in temp and humidity over the seasons.
 

JimD

Jim
Senior User
I took a minute to google up how the sawstop cartridges work. They do not use a fast burning powder to activate, they use a spring. The spring is held in tension by a wire that melts when the aluminum block is slammed into the revolving blade. The wire melts when the electronics detect you touched the blade by a change in the current it is always placing on the blade.

That leaves me a little curious about the spring design. A spring held in a compressed state for an extended period of time (possibly years) can take a set - can lose some of it's force. It looks like a pretty small spring and Wikipedia says it is applying 1000 lbs of force - doesn't seem credible for such a small spring. But if the material is at a high state of stress, it makes creep much more likely. If you got the spring really hot that would increase creep too but most of the cartridge is plastic so I doubt you could hurt the spring without destroying the plastic. The restraining wire is another potential aging issue. It also could creep and it's electrical properties could also change with age.

So do SawStop cartridges get old and need replaced? Do they say anything about that?

Wikipedia (which I realize is open access so not always reliable) says activation is supposed to be in no more than 5 milli seconds and the outside of the blade can move 10.4 inches (1/3 of a revolution) in that amount of time - enough to do the damage in the video if the thumb is moving firmly into the blade in my estimation. So it may have functioned normally. 1/3 of a revolution is right for a 5 millisecond time if the saw is 3600 rpm.
 

riggsp

Phil
Corporate Member
Gotta remember, besides stopping when the blade is touched, the reaction overcomes the clamping mechanism on the trunnion and the blade drops below the table. As the trunnion pivots downward, moving in an arc, the blade moves away from the operator. Also notice the blade in the video has “depth limiting” protrusions behind each tooth. Sawstop recommends Not to use this type blade as it can slow the reaction time of the safety mechanism.
 
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Wyatt Co.

New User
Bill
I always find it humorous when something goes wrong, or has potentially gone wrong, with a SawStop and all the SS owners have to step up and defend it.
 

petebucy4638

Pete
Corporate Member
I think that you have hit on the problem. The anti-kickback, blade depth limiting features of this blade would reduce the effectiveness of the Sawstop braking mechanism by keeping the blade from digging in to the brake as quickly as it would have done without the depth limiting features.

Pete

Gotta remember, besides stopping when the blade is touched, the reaction overcomes the clamping mechanism on the trunnion and the blade drops below the table. As the trunnion pivots downward, moving in an arc, the blade moves away from the operator. Also notice the blade in the video has “depth limiting” protrusions behind each tooth. Sawstop recommends Not to use this type blade as it can slow the reaction time of the safety mechanism.
 

petebucy4638

Pete
Corporate Member
In this case, the Sawstop owner used a type of blade that Sawstop warns you not to use because the depth limiting features on the blade keep the brake from operating as quickly as it would with a traditional blade. One of my Freud dado blade stacks has depth limiting/anti-kickback features. I still use that dado, but I am aware that it does reduce the effectiveness of the Sawstop brake.

Pete

I always find it humorous when something goes wrong, or has potentially gone wrong, with a SawStop and all the SS owners have to step up and defend it.
 

danmart77

Dan
Corporate Member
I always find it humorous when something goes wrong, or has potentially gone wrong, with a SawStop and all the SS owners have to step up and defend it.

Don't know it they are "defending" the machine or wondering if their saw will work as advertised?

If I had a SS I would still use good push sticks for most cuts. I don't have a SS myself but I do see the value of owning one.

below is a good video demo of push sticks. I love the push sticks that you can push and hold your work down.

https://www.youtube.com/watch?v=CJMPLVCYuQw
 
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JimD

Jim
Senior User
I am going to speculate a bit but I do not believe the blade design explains the extent of the injury. I doubt if the blade extended the time to stoppage of the blade by 1 millisecond - by 20%. If it did, it means it stopped in .36 of a rotation instead of .33. That would be just less than an inch of additional travel of the outside of the blade. Less is obviously better but an extra inch of travel or extra .03 of a rotation did not cause the tiny nick shown in hot dog examples to turn into a multiple stitch wound.

My logic is just that the force applied is considerable. It embeds the blade in the aluminum block nocking teeth off the blade in the process. Blade design may make a small difference in the time/rotation to stoppage but is going to happen pretty fast. If you reversed the blade, I doubt you could not get it to make half a revolution before stoppage. The number of teeth and the tooth profile also probably make small differences.

Either the cartridges age and do not reliably stop the blade as quickly when they get old, there is something wrong with the OP's saw, or we cannot expect the SS to prevent stitches if we move our hand briskly into the blade. I would love to hear from Saw Stop on this but I think the design is not adequate to prevent stitches in all circumstances. If that is the explanation, the SS still changed an amputation into a stitches situation. That is pretty significant.

This is what SawStop has on their website in the frequently asked questions page:

Can I get a serious injury using a SawStop saw?
In the vast majority of cases, coming in contact with the spinning blade will result in a minor cut. However, if your hand moves into the blade at very high speed, it is possible for you to receive a serious injury.
 
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gmakra

New User
George
My following comment in general is not about Saw Stop its self but technology in general.
Technology is a useful tool, but more and more it inserts itself in to our lives and creates a false sense of security while it undermines our need for common sense, self awareness and knowledge.
If you lost your phone who could you call? Bet ya all your contacts are on your phone and you don't remember a one of them including your home number. Ask me how I know.
Take GPS it has pretty well has replaced the map and trip planning.
And guess what it works most of the time but not always.
How many times have you ended up someplace you really don't want to be!
Look at how many different apps are out there to make our lives easier! Do they?
The wife wanted a robot vacuum cleaner for our cabin.
Lets say the marketing is so much more than reality.

I was told as a kid " to keep my hands away from moving parts!"
Be responsible for your actions!
Today not so much anymore.

I would not buy a Saw Stop personally cause its too finicky and no matter how much you try to engineer out the human they will always figure out a way to beat the machine and get hurt.
Me I know my old Delta machinery is beautiful, functional and very dangerous every time I use it which keeps me from doing any bone headed moves.
 

JimD

Jim
Senior User
I am probably over analyzing this but I am thinking of getting a SawStop before I retire so it is an interesting topic to me.

If the blade stops in .005 (5 milli seconds or less) as SawStop states, it makes sense to me that the injury will be a function of how far into the blade your body part moves in that amount of time.

How fast can we move our hands? One way of measuring this is to look at how fast a human can throw a baseball. 100 mph is not unusual for pitchers. I found claims of 150 mph hand speeds googling. At 100 mph, a hand would move 8.8 inches in .005 seconds. That seems to be obviously enough movement for there still to be an amputation. At 10 mph, your hand could move the width of your finger in .005 seconds.

We aren't winding up in a throwing motion in our shops, at least not when pushing things through the table saw blade. But if a board breaks or something and we are pushing that board, our hand could move pretty fast towards the blade. Seems credible to me I could still loose a digit with a SawStop saw. The OP illustrates it is possible to get a pretty nasty cut.

To me the bottom line here seems to be that we cannot count on a Saw Stop saw from preventing our injury. It will reduce the severity in all but the most extreme hand velocity situations, at least, but we still have to use good practices or we are going to need some stitches.

Saw Stop shows pictures of injuries on their website from people using their saws. But they are all the superficial hot dog type. That seems at least potentially dishonest to me. They have to know there have been others. If my math is right, stitches are not really all that unlikely. They admit in their FAQ that there could be a serious injury. If they know it has occurred and have access to the pictures, should they post them?

If the actual correct picture here is that Saw Stop saws are nice saws that add a measure of protection but do not prevent serious injury up to and including amputation, would everybody that has one have purchased it? Would most people still buy it?
 
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