Saw Stop...How do they do that?

[Bill Space]

Hi,

I saw mention in previous thread(s) that the saw stop system somehow checks itself and can determine if it is functional or not. This was related to the question about painted blades possibly insulating themselves from the main part of the saw (electrically).

I can see how the SS system could be set up to check for something that might be touching the blade when the blade is stopped, something that might cause the system activate when when the motor was started.

But, is the system able to detect a blade that is electrically insulated (by paint) from the saw arbor? I believe this is unlikely to happen, but it could.

As a mental exercise, lets say we somehow attached cutting tips to a plastic disc. Could/would the SS system detect this? Would the system either prevent the saw from starting, or somehow still protect the operator if he placed his finger against the blade while it was turning?

More realistically, say it was a standard painted metal blade, but there was paint on the bore of the arbor hole and the sides of the blade, and that this insulated the blade from the arbor as far as DC resistance goes. Does the SS system use AC and essentially pass current through capacitive coupling between the blade and the arbor, with the paint being the dielectric? If so perhaps this could be the way the issue of insulating paint is eliminated.

Just curious...as I see how the system could easily determine if,while the motor was stopped, the setup was sensing something that would cause the system to activate if the motor was started, but I don't see how the system could easily determine if there was something present that would inhibit the system from activating when needed.

I know the SS system is a great improvement over what we normally have to protect us in the worst case (nothing but luck). But I would like to understand what the limitations are, something that must be there, as nothing is absolutely perfect...well, almost nothing, just in case my wife is watching...:-)

Anyone?

[ray hampton]

I do not know the answers either but I intend to watch the post for the answer

[glenn bradley]

No expert but, the circuitry is far more advanced than just a continuity checker ;-) I imagine there are thresholds that must be met from several sensor locations, the blade to cartridge relationship possibly being one. If the blade does not adequately conduct, that test would fail. Just speculation.

[Richard Wolf]

If you used a plastic blade, the saw stop would detect "no blade" and not allow itself to start.

[Kyle Iwamoto]

The saw goes through a self check each time it starts. If it senses that the blade is either not installed or gap too far and the brake won't work, the saw will not start. You can test it by touching the blade with the saw not running. Works well. I use Teflon and painted blades. They work. I can touch the painted part and the saw will sense it. I don't know how that works, but it does work. Something to do with capacitance. Bottom line, if the brake won't work, the saw don't start. It's a smart saw. I was concerned when I first put a Freud blade on......

[Bill Graham]

I sometimes run a sanding disc on the saw so when I got my CNS I emailed SawStop TS to ask if this would interfere with the safety system. Here's the reply:

"Hi Bill,

A sanding disc will work on your SawStop saw. It needs to be 10” in diameter to allow you to properly set the spacing between the sanding plate and the brake cartridge as you would with a 10” saw blade. Keep in mind that if you touch the sanding plate with a finger the brake will activate and not stop the plate before sanding off a good amount of your flesh. The braking system depends on the teeth of the saw blade digging deeply into the aluminum brake shoe to get the blade stopped quickly. This will not happen with your toothless steel plate.

Thanks,
Tom"

Sent my thanks back:

"Thanks, Tom for the quick reply. Just wanted to make sure the abrasive discs wouldn't set off the brake since they cover the plate all the way to the arbor hole."

And got this reply:

"Hi Bill,

Sometimes customers assume or are told by a dealer that the blade needs to make contact with the blade shaft in order to work. The issue usually comes up in reference to the red Teflon coated Freud sawblades. We have had several customers sand off the coating where the blade sits against the blade washers. This is not necessary as the electrical signal on the saw blade is a radio frequency signal that couples right through any coating on the blade. In your case, instead off the Teflon coating, your coating is a piece of sandpaper. This is not a problem. The only danger of an unnecessary activation is if the sanding plate makes contact with the aluminum brake shoe on the brake cartridge. This spacing is adjustable and needs to be checked each time you remove your saw blade and put on the sanding disc and vica-versa.

Thanks,…"

HTH,
Bill

[Julie Moriarty]

I have a number of Teflon blades. There is no Teflon coating inside the arbor hole and all are conductive to the cutting tips on the blade. FWIW...

[Andrew Pitonyak]

... the electrical signal on the saw blade is a radio frequency signal that couples right through any coating on the blade.

Interesting, so the blade acts as an antenna. I wonder what frequency...

[Mark Burnette]

The "gap" comments make me wonder--Does the system work with undersized blades like stack or wobble dadoes, molding heads, etc?

[Alan Schwabacher]

The "gap" comments make me wonder--Does the system work with undersized blades like stack or wobble dadoes, molding heads, etc?

Dado sets (8") work fine, but require a different and appropriately sized brake cartridge than do 10" blades. Molding heads don't work properly on a Sawstop, because the cutters are far enough apart that they could not be stopped for certain before they had traveled far enough for significant damage.

[Mark Burnette]

But the system can be bypassed & the saw used with such options?

[mreza Salav]

You cannot start the saw without a proper size blade and brake installed, period.
The bypass mode can be used by turning (and holding the key for a few seconds) every single time you start the saw (i.e. if you stop the saw and start again it wont' be in bypass unless you follow the procedure again).

[Michael Dunn]

Interesting, so the blade acts as an antenna. I wonder what frequency...

According to my understanding of what I just read I wouldn't say the blade is an antenna. I think they're emitting RF from somewhere in the saw. Then when that RF is interrupted it triggers the safety feature. Either way, pretty ingenious stuff.