There is a removable cartridge that stops the blade. It ruins the blade. The cartridge gets swapped out with a new one in a few minutes (the table top of the saw can be partially opened) and costs about $150 .
> When the brake is activated, the most recent data is stored into memory and SawStop can download the data from the activated cartridge. This data is very important to our continuing research and development program. If SawStop’s engineers verify the activation was due to contact with skin, you will receive a free replacement cartridge. If you are unsure why the cartridge activated, you can also ship the cartridge for analysis to SawStop’s service engineers. When the cartridge data is downloaded, we then can determine what specifically caused the brake to activate so that further unintended activations can be prevented. The brake cartridge evaluation is free of charge the shipping of the brake cartridge is paid for by the customer.
It _may_ destroy the blade. I've had mine for about 10 years, and have had two false triggers in that time (both times, dumb mistakes on my part). Neither time has the blade been destroyed.
I sometimes mill my own lumber from windfall on my property - in the first instance somehow I managed to put a single piece of near green lumber (~40% moisture) in the same rack as some lumber I knew was dry.
A few weeks later I needed some scrap for something, grabbed the piece closest on hand, pushed it into the blade and immediately triggered the wet wood alert and the blade spun down slowly. I knew that the wood wasn't wet, so started the saw up again and pushed it straight back into the blade only with more force, triggering it straight away.
Second time was due to cutting a lot of pitch heavy pine over an extended period of time - it built up on the cartridge and after a blade change that I didn't check the clearance on, it bridged the brake with the blade (i assume) and triggered on start up. (It comes with a tool to check this clearance after a blade change - I of course did not follow the instructions).
You can use wet wood or pressure treated lumber or even foil coated acrylic - but the key is that you need to be expecting this, and you put the saw in to by-pass mode.
At that point, it's just another dumb saw that will chop your finger off, but it won't trigger the cartridge, and you can make what ever cuts you need.
The way it tries to determine if it's wet wood / a body part is the capacitance change. Slightly different profile which they can use to make an educated guess (obviously erring on the side of caution).
This is why for some time they would give you a free cartridge if yours triggered on flesh - they wanted the data on there from real-life flesh contact to improve their calculations.
> This is why for some time they would give you a free cartridge if yours triggered on flesh - they wanted the data on there from real-life flesh contact to improve their calculations.
The automatic defibrillators manufacturers also will often send you a unit for free if you used your unit for an actual defibrillation. Same idea.
Ah, that explains why there is so much electronics in the cartridge! It seemed a bit like overkill, but returning the cartridge will get them their data.
You can manually disable the auto—trigger mode in those situations though (bypass mode).
It also doesn’t like anything conductive - so anything coated with Mylar, any kind of conductive dust or debris, etc. is also a crapshoot.
Very much edge cases though, unless you’re dealing with a lot of randos. A workshop I used to share had a wall covered with sawstop ‘trophies’, due to people doing weird stuff.
I've triggered one by touching the blade too soon after it has stopped. There is a short delay between when the blade stops and when the brake is disabled. I've also had one trigger on a heavy miter through some gnarled 8/4 walnut.
Actually not.
My handguard saw will do as well as the sawstop non-destructively (independently tested and verified, so you don't have to take their word for it).
They do it (basically) by predicting whether your hand will touch the blade, rather than waiting until it does touch the blade.
If you wait until someone actually touches the blade, then yes, you have to operate very very fast. That is unavoidable due to physics, as you say.
But if you can gain 100ms or 250ms by proving a 100% probability that the hand will touch the blade before the person can stop it, you now have a lot more time to stop the blade.
Ive looked at the saw you mention in another comment, and in all honesty Id much rather have a safety precaution that works based on very simple physics (like sawstop) than some black-box ai hand detection algorithm.
Finger movements are generally on the order of 1-2Hz, a hand holding a large piece of wood will generally be much lower than that, which means that at the hundreds of millisecond level most of the movement can be predicted from momentum alone. Something which identifies and tracks hands in a view and fits a second order model to the movement can likely predict accurately enough at that timescale to make for a meaningful safety improvement (especially because if it's non-destructive you can tune it to err more on the side of caution than a destructive option)
Holding a piece of wood and sliding it along a table saw (to cut it) is the canonical method for losing a finger, and you could definitely pick that out with a relatively simple bit of computer vision.
also, the saws do not produce dust everywhere.
these are European saws. Dust extraction is not only required on the saw, It’s required by law in the workplace.
This saw will not operate unless the safety + extraction hood is in the proper position and dust extraction is hooked up
I can show you a video of an air quality meter sitting between the cameras and the saw hood if you want. The amount of particle change is minimal
The blade doesn't have to stop. Some saws have the entire blade assembly lower. If you walk the table saws at AWFS you'll see all types of different safety systems.