SawStop false brake activation

[glenn bradley]

Thanks for following up Eric.

[Simon MacGowen]

He said it as a low possibility, but possible that the riving knife holder (NOT the handle) could have been the trigger. He also said that it wasn't a bad idea to put a small piece of cardboard in the riving knife holder and clamp it down to keep it from "rattling".

I am totally not buying this conjecture. I happened to be at the shop with the ICS and took a look at the holder which is probably half an inch or more away from anything. The loose part of the holder is an about 1/4" metal and could move only 1/16" (?) or so when I shook it here and there after releasing the lever.

How could the vibration of the saw (minimal) cause a contact between a blade and the holder UNLESS the blade is set outside the SawStop recommended limit. In that case the activation would be caused by the contact between the blade and the brake, not with the holder.

Anyone who has an ICS or PCS can easily verify my reasoning by looking into their saws. Even if it is a very very low possibility, since such caution has not been spelt out, I would demand SawStop reimburse my blade/dado cutter -- that is if I could prove the conjecture.

Nonsense is all I can summarize about the SawStop guy's conjecture...not to mention that no one I know has ever activated a dado cutter due to "vibration" in the past 12+ years. If he did not know the answer, fine and say it but don't treat us like idiots without thinking ability. The possibility is ZERO if one has the holder in front of him.

Simon

EDIT: Now that I have access to the PCS, here are the measurements: dist between blade and riving knife: 3/8"; between blade and holder: 1/2". The loose part of the holder could move about 1/16". In other words, the blade would contact the riving knife long before it hits the holder (anywhere of the holder, including the handle!). A low possibility? Lower than I could win the next lottery...

[Peter Christensen]

I'm kind of in Simons corner except he is looking at the normal blade and cartridge distances. The dado blade being 8" would be inch further away from the riving knife clamp or handle. While I'm glad they are sending you a new brake they should step up for the dado set too unless they can prove the misfire wasn't something you did. This coming from an ICS owner by the way.

[sean meltvedt]

Simon & Peter the blade is not making contact with anything. The theory is the riving knife clamp contacts the brake, not the blade. Hopefully this make more sense.
Sean

[Eric Anderson]

The sawstop tech also indicated that there is some RF signal involved with the break and that is why you need to properly gap the blade and break with the yellow "feeler gague". So somehow this RF signal may mean you actually don't have to touch. And as Sean said, it's the break not the blade that caused the trigger. Fortunately, since there was no real speed in the trigger, my Dado blade is not harmed (again 400 ms, less than 1/2 of a second), possibly dulled slightly, as there wasn't a lot of speed built up yet. none of the well documented "bangs" people tell about, infact no noise at all.

[Simon MacGowen]

Simon & Peter the blade is not making contact with anything. The theory is the riving knife clamp contacts the brake, not the blade. Hopefully this make more sense.
Sean

Thanks for your addition information.

The theory of the clamp touching the brake is as good as the "vibration" causing an activation. Again I did some measurements, this time about the clamp and the brake -

- dis between the brake and the underside of the clamp: 3/32" (1/32" x 3 as I could insert three credit cards between the clamp bottom and the brake)
- the clamp level is about 1/4" from the side of the brake (by sight)
- the loose part (jaw) of the clamp could not be moved down

The recommended spacing between the blade and brake is from 1/16" to 1/8". In other words, anything less or more will affect the brake operation. Too close it may cause an unwanted activation, too far the braking effectiveness may suffer.

3/32" is how far the bottom of the clamp is away from the brake. If a spacing of 1/16" is safe from causing an activation, how could the clamp with a spacing larger than 1/16" cause a misfire?

Any one of you is concerned that a misfire would happen due to the clamp/vibration, please double check your spring-loaded clamp installation. The reason the clamp could be too lose to the brake and cost you a brake replacement is that it has not been installed properly.

A lot of people use the SawStop (say with a cross cut sled) without the riving knife installed. The loose clamps do not seem to have caused misfires. As I already said, my dado cuts and others I have known have not resulted in any misfires.

Please correct me if or where I am wrong in my analysis. I would be happy to change how I use my SawStop to reduce any chance of a misfire.

Simon

[Simon MacGowen]

The sawstop tech also indicated that there is some RF signal involved with the break and that is why you need to properly gap the blade and break with the yellow "feeler gague". So somehow this RF signal may mean you actually don't have to touch. And as Sean said, it's the break not the blade that caused the trigger. Fortunately, since there was no real speed in the trigger, my Dado blade is not harmed (again 400 ms, less than 1/2 of a second), possibly dulled slightly, as there wasn't a lot of speed built up yet. none of the well documented "bangs" people tell about, infact no noise at all.

Please see my response regarding the spacing aspect.

Unless there is product defect in the cartridge, the RF signal would not activate the brake because no part of the clamp is closer to the brake than the blade/dado cutter is to the brake.

If I had to venture, could there be sawdust (in a humid shop) collected underneath the clamp that reduced the bottom spacing from 3/32" to under 1/16", causing an unwanted activation?

I would probably look further into the clamp set-up than believing that a properly installed clamp was the reason for the misfire. If the latter were the cause, I would categorize it as a design defect.

Simon

[Jon Nuckles]

I missed this thread when it was first posted. I had a trigger on start up with a regular blade cartridge when switching back from the dado blade to the regular blade. Same thing as the OP reported: immediate activation and no loud bang -- more like a click if I recall correctly. The tech said it was likely that the brake was set too close to the blade and I didn't question that theory. I had assumed that the saw would not start in that situation, but apparently it does. Sawstop did not offer to replace the brake and the blade was not damaged. I now make very sure to check the lights when changing blades rather than relying of the gap gauge. I haven't had any further false activations.

I did have a real activation around a month ago when kickback pulled my hand back into the blade. I got cut bad enough to require an emergency room visit and stitches, but I might have lost part of a thumb and finger without the brake. Sawstop does send a free replacement cartridge when you send in the one that sensed flesh, and I received that. I bought the saw mostly for it's superior dust collection and at my wife's urging rather than for the safety feature, which I was confident I did not need. I'm glad I had it.

[Simon MacGowen]

I now make very sure to check the lights when changing blades rather than relying of the gap gauge. I haven't had any further false activations.

I bought the saw mostly for it's superior dust collection and at my wife's urging rather than for the safety feature, which I was confident I did not need. I'm glad I had it.

Good reminder on the checking. I always wait till I see a solid green. (I also unplug it like working with a router and changing a bit before I do anything with the blade or riving knife! The switch alone is not enough for me.)

Every time I reset the gap, I make it sightly more than the min. (the plastic gauge), but still way under 1/8".

Your wife is good at keeping you safe!

Simon

[Roger Feeley]

What's this feeler gauge stuff? I didn't get a feeler gauge with my ICS 6 or 7 years ago. Is that a new thing? I think back then they said to use a nickel. The very first time I tried using a nickel, I dropped it down into the saw (might still be down there). So I found a piece of acrylic about nickel thickness and tied it to a string. There's a magnet on the other end. I keep it up on the dust collector arm with some other Sawstop tools in a little caddy. When I change blades, I plop the magnet onto the bed and I don't lose the gauge.

I guess you could say that I have an 'Idiot Gauge'.

[Roger Feeley]

Seriously, one indication of blade speed is the depth to which the blade teeth dig into the brake. A great guy at SS (Hi Roger) told me once that the worst thing is when somebody uses a tape to measure the blade to fence distance and touches the blade before it has come to a full stop. The brake fires and there just isn't enough kinetic energy to drive the teeth in much. Roger said that those are really hard to pry off. So, if the saw is just barely powering up, the blade shouldn't have dug in as far.

I've had two brake fires, both due to my mistake. On one, it was really hard to get the brake and blade off. Roger told me that I probably had adjusted the brake just a bit close. SS will still work ok but if you have a brake fire, the spring doesn't extend quite as much and there's more pressure. Those two events were in the first few months and I haven't had a brake fire since.

[Simon MacGowen]

What's this feeler gauge stuff?

http://sawstop.3dcartstores.com/Blad...ge-_p_158.html

It sets the gap slightly more than 1/16" (the min.).

Simon