Sawstop - Cutting Hidden Nail.

[petebucy4638]

Today, I was cutting a piece of hard maple on my Sawstop Professional table saw when I saw a spark. The brake didn't trip (for which I am grateful). After turning the saw off, I remove the board from the saw and found what looked like a small brad that had for some reason been driven into the board. The saw blade, which was ready to be replaced anyhow, had a chunk knocked out of two teeth.

I thought that making contact with metal would trip the brake.

 

[Echd]

As the nail was still within the (relatively not conductive) wood, it never triggered the stop. By the same token, if you jumped in the air and touched the blade, it probably wouldn't trigger until you touched the ground (or something touching the ground).

Think of a squirrel on a powerline. When does he get zapped?

Now, if the nail had been close enough to the surface to touch the cast iron tabletop, it would have blown. And depending on the wetness of the wood, if your hand had been guiding it it might have... maybe.

 

[Westpacx3]

Mine has also cut brads by mistake with no issues

 

[petebucy4638]

I suspected that it had something to do with the Brad not being in contact with ground. Thanks.

 

[Westpacx3]

The rep told me at thw Klingspir Hickory make over opening that Brads are not a problem. Probably for all the above reasons

 

[Ricksmi]

I have hit small nails and only issue is needing a new blade, I have cut wet PT and had zero issues and learned wet wood and nails are not an issue for the most part. Found several youtube videos where people tried to activate the brake with wet wood even pouring water on the wood, nails and even cutting aluminum and had no issues. I'm not going to go that far on mine but if I have to cut aluminum I'll just turn the safety off.

 

[Echd]

I have cut aluminum on mine quite a bit and always turn the safety off. I wouldn't expect it to NOT trigger on aluminum.

My one trigger on my SS was on some foil backed OSB. I bought it because it was on clearance and didn't even think about the foil being a problem... until it immediately triggered. Not so cheap after all, unfortunately.

I have had fresh PT lumber that I turned the safety off for, as testing it showed that the safety would have been triggered, so be very careful. My experience is that it isn't hard at all to find PT lumber that can trip the safety. That said I don't cut PT lumber often on a cabinet saw, but I did do a privacy screen for my mother recently that needed to be made of PT as it was going near her hot tub outside. I am very cautious cutting any construction lumber, pt or not, due to how wet it often is, but I've never found any construction lumber that would have triggered.

 

[petebucy4638]

I have hit small nails and only issue is needing a new blade, I have cut wet PT and had zero issues and learned wet wood and nails are not an issue for the most part. Found several youtube videos where people tried to activate the brake with wet wood even pouring water on the wood, nails and even cutting aluminum and had no issues. I'm not going to go that far on mine but if I have to cut aluminum I'll just turn the safety off.

I suspected that the Sawstop blade brake relied on grounding, but I think that it must be something more sophisticated. If you were standing on an insulated mat or wearing rubber soled shoes, then you are not going to be grounded. How Sawstop detects contact with an ungrounded object is something that I don't understand at this time.

 

[bowman]

It's the ability to detect a path of conductivity. If you're holding an aluminum fence and the blade hits the fence, it will trigger. If you had your finger on the head of the nail, it should trigger. I was not barefoot when i triggered on my fence, maybe i was touching the saw with my other hand, i don't recall now.

 

[petebucy4638]

I think that the attached image explains how Sawstop detects when it touches a finger. It is not looking for ground; instead, it detects the conductivity of what comes in contact with the blade. That is ingenious.

 

[Echd]

It still has to have ground. If the conductivity alone were enough, your nail would have triggered it. You can test all manner of things with it by using the lights on the panel to check it out yourself.

It's really just a super powered version of one of those old school touch lamps.

 

[Rwe2156]

It's the ability to detect a path of conductivity. If you're holding an aluminum fence and the blade hits the fence, it will trigger. If you had your finger on the head of the nail, it should trigger. I was not barefoot when i triggered on my fence, maybe i was touching the saw with my other hand, i don't recall now.

You don't need to be touching an aluminum fence for the brake to trigger. I was curious about it and pushed my aluminum miter fence onto the blade using a stick and the red light went off. No, it wasn't running.

I've hit a few screws. It's a common misconception a nail will trigger, most I've seen by the anti-SS crowd.

 

[cobraguy]

During a conversation with the SawStop rep one day at Kilingspor, he said the brake technology is more like the way the touch screens on phones, tablets, etc work. So the observation that it's more sophisticated than just a grounding path is spot on.

 

[Hmerkle]

It still has to have ground. If the conductivity alone were enough, your nail would have triggered it. You can test all manner of things with it by using the lights on the panel to check it out yourself.

It's really just a super powered version of one of those old school touch lamps.

This is why they can't put the technology into the Festool CSC SYS 50 - no ground - it is a battery operated saw. The "Signal" is a ground-path connection that changes ever so slightly to trigger the brake.

 

[JNCarr]

Capacitance. No need for a ground loop.