Is a sawstop brake misfire possible?

[Paul Steiner]

Myself and a colleague are very interested in the Sawstops and we are trying to get one for our school shop. In researching the SS we came up with an interesting question. Is it possible to get the SS to misfire the brake, costing you $150? The SS detects the electric current in your body and triggers the brake, is there anything you may cut that would cause a misfire? Having worked at a school for 5+ years I have been asked to cut many strange things.
We thought about it and came up with some possibilities: cutting aluminum, cutting an item with metal foil backing(insulation, magnetic whiteboards), cutting an item from an organism like ivory or bone or antler, cutting items with enough moisture to allow for conductivity-treated lumber that came in from the rain.

Have you had or heard of anyone having a misfire?

[Mike OMelia]

Green wood can cause a misfire (at least Sawstop says so). That is why they build in a lockout mechanism that allows you to turn off the protection. I'm sure if you read the fine print you will find that while in this mode, you forfeit all liability claims.

Mike

[Matt Benton]

I'm pretty sure that you can bypass the brake for just such ocassions...

[Scott Wigginton]

IIRC you can also test diff materials and it will tell you whether it would have triggered the brake or not. Too late for me to dig around but I'm pretty sure I saw that while reading one of their manuals.

[Myk Rian]

Green wood, treated wood, staples, and nails will set it off. The trigger mechanism senses a ground.
Of course you can't cut non-ferrous material without it tripping.

[Jason Beam]

Just a note about the whole ground sensing thing ... technically it does not sense ground - it's actually more like capacitance... from their "How it works" page:


The SawStop safety system includes an electronic detection system that detects when a person contacts the blade. The system induces an electrical signal onto the blade and then monitors that signal for changes. The human body has a relatively large inherent electrical capacitance and conductivity which cause the signal to drop when a person contacts the blade. Wood has a relatively small inherent capacitance and conductivity and does not cause the signal to drop.

Ref: http://www.sawstop.com/how-it-works-overview.htm

[Don L Johnson]

I tripped the brake a couple of days ago and all it came into contract with was my phenolic miter board (built by Jointech). It just brushed the side of it, and POW!!

[William Nimmo]

You can test an item by touching it to the blade without the saw running. The light on the front will go red if it will trip the brake. Stay green if it is good. I do not know if sawstop regards this as a real test, but it is what I do.

[Barry Richardson]

We had one misfire last week, set up with a dado. As far as we can tell, the blade didn't come into contact with anything other than the sheet of plywood. The blade was beneath the sheet about midway through the cut. We looked for metal particles alond the cut (I've heard stories of ply having some weird stuff imbedded in it) but saw nothing. Sawstop states that if the brake fires for no aparant reason, sent the fired cartridge back to them and they will send you a free replacement cartridge. We sent it back, we'll see if they hold up their end of the deal. We are still stuck getting all the broken teeth on the Forrest Dado set repaired.

[Kevin Groenke]

Hey Paul,

There's plenty of information here and elsewhere about the technical aspects of how SS works and the fact that it can stop when you don't want it to. So I'll stay out of that.

We've been running 2 SS's since 12/04 in a post-secondary student shop. In that time the saws have collectively stopped 15-20 times, so our "insurance" cost has been ~$1500. Though the cause of a couple of the stops was not immediately apparent, all but one was explained after SS analyzed the cartridges. All of the other stops were fairly clear cut user error (aluminum, foil, miter gauge, jig, tape measure, riving knife, blade/cartridge gap, etc...) SS replaced at least 5 of the brakes in which the cause was somewhat suspect. 2 stops were the result of saw/person contact: one of those was at the end of spool down which probably wouldn't have caused significant injury, but one was a direct thumb/blade contact which could have resulted in significant injury (who knows?). So, to date, we have bought new saws and spent ~$400/year for an insurance policy (albeit imperfect) against blade-contact related tablesaw injuries. An incredible value IMO.

[Don Bullock]

From what I have red on this forum and others, the most common SawStop misfire problem seems to be caused by metal, especially the miter gauge. People seem to misjudge where the end of the miter gauge will be as it approaches the blade. I've seen many pictures of miter gauges with nicks from table saw blades.

Check out post #32 in the following Sawmill Creek thread on SawStop for one shop's experience with misfires -- http://www.sawmillcreek.org/showthread.php?t=97034

[James Williams 007]

My Dad misjudged where his miter gauge was an tripped his while he had his dado blade on. I would recommend the SS for a school shop but I would stick to cutting dry wood.