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Comment by CraigRo | Hacker News Reader

People will disconnect the safety system, and we'll have a 500$ saw with a 300$ piece of useless gear

There are lots of things you can't saw with a sawstop, and if triggered, it is very expensive to replace

You don't need to disconnect anything, you can start a saw-stop up with safety temporarily disabled using a key that comes with it. A good thing to do any time you're cutting pressure treated wood.

Does the pressure treated wood trigger the safety device?

And is the safety device "destructive" to the saw (requires expensive parts/repair/etc to reset)?

Yes its destructive. Its a gunpowder charge that forces an aluminum block into the path of the saw blade.

It works by detecting changes in capacitance so yes some treated wood and wet wood can set it off.

But it's not destructive to the saw itself, the aluminum brake is a replaceable part.

It destroys the blade too.

The replacement parts are often more expensive than an entire cheap table saw.

If it saved your finger? Worth it.

If you forgot to disable the feature and cut some wet or pressure treated wood and triggered it? Very irritating,

> If you forgot to disable the feature and cut some wet or pressure treated wood and triggered it? Very irritating,

Scares the shit out of me every time too. I often have the garage door closed due to weather or to limit noise and it’s like a gun going off in an enclosed space.

I never use power tools (even a vacuum cleaner) without ear muffs.

I use hearing protection. It's a lot louder and more sudden than a power tool, especially when amplified in a small enclosed space. If I were on a shooting range it'd be no big deal, but not unexpectedly in my garage.

Pressure treated wood is electrically conductive enough for the saw to think skin is touching it

Yes, anything that can conduct electricity in the wood will trigger the safety device. Pressure treated wood is often so wet with copper based preservatives that it’ll trigger the safety circuit. Old nails in wood, your finger, hand, etc will also do this.

And yes in general the blade and brake are both trashed because of the wild deacceleration forces that happen instantly. Frustrating when pressure treated wood causes this, humbling when your hand caused it.

Nails alone usually won't trigger the brake. The nail would also have to be in contact with something conductive or else there's nowhere for the current to go.

It can trigger it yes, and it is destructive to the saw blade and safety device, and can ruin the clean cut of the piece, though may or may not ruin it entirely. Good saw blades aren't cheap, and neither is the safety device. I'm unsure of what wear and tear it has on the motor itself, they can at least endure a few triggers for certain and I doubt it's "good for it" but unless you're doing it frequently I also doubt it likely to ruin the device itself but admittedly am not sure about that.

And to be clear, it's well worth it IMO. Of all the tools I have in my shop, the Table Saw is easily the most dangerous. If I had long hair the Lathe would give it a good run for it's money though. I refuse to use a table saw without a sawstop (or similar safety break). The one I have and others I've used all have a key to insert to disable the safety device If need be.

I doubt it's amazing for the bearings, but you can replace those fairly easily(*) on most motors.

(*) for people who have a workshop, anyway

My dad was a machinist when he was younger. My siblings and I grew up with a well-equipped home shop, including a table saw, a drill press, a milling machine, and my dad's pride and joy: a two ton metal lathe. He drilled into us the importance of safety for all the tools, but the most vivid lesson was the story about the drill press: When he began his apprenticeship, he noticed a large photo on the wall of the shop of a long pale stringy thing. He asked what it was. It was a tendon which had been yanked out of the arm of someone whose hand got caught in a drill press. I still think about that whenever I use a drill press.

In metal shop in high school, there was an 8*10 photo on the wall behind it of a long haired teen with about a third of the hair yanked out.

My dad (military) never did like long hair. He said it was just a convenient handle for someone to pull back your head and cut your throat.

Yep, a common motto in the machine shop is "If it spins it wins"

The sawstop triggers when the blade contacts something conductive (like a finger), and needs to stop fast enough that when that happens the finger isn’t removed first.

It manages to do that within a few teeth, which is quite impressive at 1000+ RPM.

It does this by firing an explosive charge which shoves an aluminum block into the spinning blade, while dropping the blade below the level of the saw deck.

Essentially a type of airbag like braking action.

That is how it can turn s situation which would guaranteed an amputation into a minor scratch.

It can (and does) get easily triggered by things like conductive wood (pressure treated), nails or metal in the wood, metal coated plastic, etc.

Every workshop I’ve been at that has one has a collection of triggered/destroyed blades hanging on the wall.

It could undoubtably be done cheaper than it currently is ($30 a brake?) but as designed it’s destructive - and it’s hard to imagine a effective way to do what it does that isn’t destructive.

The brake is like $80-90 and contains a computer that collects telemetry. If it triggers for a reason other than user error you can send it in for a refund.

It doesn't drop the blade, just stops it cold (at least on the model I've used). The Bosch system dropped the blade (thereby avoiding destructive damage to the blade and brake) but they were cease-and-desisted by SawStop and unable to sell it in the US.

The one I used, and their website, says that they drop the blade. [https://www.sawstop.com/why-sawstop/the-technology/], but I’m not clear on all the models. It’s been years since I’ve used one. Glad they’re cheaper now!

Never having used one of these before, is there anything (ideally conveniently built in) that you can use to know before you cut a particular material whether it'll trigger the stop? Touch it against the blade while it's not running and see whether an LED lights up, or similar?

(I think it's unambiguously a good thing to mandate, but I'd also prefer not to have to memorize a table of materials and their interactions with the stopping device...)

There are LED indicator lights that flash red when it detects a current drop. When the blade is not moving, you can touch it with your finger to see. In theory you could do this with whatever material you're going to cut. If you're cutting metal, it's pretty obvious that you need to disable the brake system. Usually where it's iffy is pressure treated lumber. Sometimes it'll trigger, sometimes not. Really depends on the moisture content of the wood and that can vary greatly. "testing" by touching the material to the blade with your hands on it might or might not indicate that the brake would fire. The points you're contacting could just not be that wet.

Most cheap lumber I see these days has a lot of moisture in it, treated or not. I’m surprised this works at all for anything short of quite-nice stock.

Pressure treated wood is also soaked with copper azole, which I believe increases its conductivity.

If you manage to cut metal with a table saw, you are a much braver person than I am

Aluminum cuts just like wood on a table saw. I wouldn't recommend trying to cut hard metals.

With the right blade, I would think that is possible. When a piece of wood kicks back and hits me it leaves a bruise through the clothing I wear. If a piece of aluminum kicks back and hits me, I imagine it would be nearly fatal.

I've always just used a regular dull-ish wood blade... never died. Survivorship bias?

Iron and steel? Of course not, go get a cold saw for that. But it's no problem and very common to cut soft stuff like aluminum and copper on a table saw.

> Never having used one of these before, is there anything (ideally conveniently built in) that you can use to know before you cut a particular material whether it'll trigger the stop?

You use a $40 “wood moisture meter” to check the water content of the lumber before cutting. If you want a built-in one I suppose you could duct tape it to your saw.

https://www.kleintools.com/catalog/environmental-testers/pin...

What about some suggestions offered in good faith?

That is how you measure the moisture content of wood, with a wood moisture meter. There’s no reason for a handheld $40 tool (that any serious woodworker will already have on hand, and one that will likely fail at some point) to be built in to a multiple thousand dollar table saw.

You can also not wear your seatbelt, not wear a helmet, play lawn darts, etc.

If every table had a sawstop mechanism, most people would use it.

1. Seatbelts are mostly passive, so not a good comparison 2. Same thing with helmets 3. Lawn darts is not a safety mechanism, it's a sport

A closer comparison would be car airbags, but a type of airbag that has false-positives and deploys when the operator drives on a particular type of road surface, in which case the manufacturer calls it "user error" and tells the operator to disable it for that type of road surface. The road surface might appear the same to the operator, so needs to be tested carefully with special equipment before the car is driven on it. And since the active safety system is disabled for this surface, the operator has now paid for a safety system they cannot use, due to manufacturer incompetence

> if triggered, it is very expensive to replace

What a silly argument!

It will be more expensive if it isn't triggered.

Unfortunately there are lots of materials run through a table saw which can trigger a sawstop. A false positive destroys the blade. Decent blades cost several hundred dollars, and are intended to be resharpened and last for many years.

I belong to a community hobbyist workshop. There are a lot of rules, lockouts and a key in place around the table saw usage, but they won't install a sawstop because they can't afford to keep up with the wasted blades.

Personally, I think I'd rather have one, but I can absolutely see why people would disable them if they were mandatory.

And after this change passes, the hobbyist workshop won't have a table saw at all.

I can only imagine the medical fees for rebuilding a shredded arm in the US

Probably $9k with pretty good insurance, $17k-$20k with poor insurance (but nb the math on the good insurance probably works out such that you’re paying very close to that difference for sure every single year, in premiums)

Plus tens of hours arguing with provider billing departments and insurance. You’ll pay over what should be your max if you screw any of that up. Time lost and stress and confusion over sorting out new bills still showing up in the mail two full years after treatment was performed.

Also it’ll be a lot worse if you lose your job after.

If you don’t have insurance, you’re getting it patched up at the ER “for free” (you’ll be declaring bankruptcy soon) but not getting most of the follow-up work done. Even if your arm could be made right, it won’t be. Good luck with the nightmare of getting and maintaining disability pay-outs.

Oh and double the out of pocket costs if treatment spans two billing-years.

It's not expensive to replace, the brake is like 100$ and it sure beats a 10,000$ hospital bill and a couple digit amputations.

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