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Comment by alistairSH | Hacker News Reader

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, 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.

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!

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"

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

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