Sawstop Dado brake fired

[Dave Sharpe]

This is an email I've just sent to Sawstop customer service - I thought I'd post here also for input from the Creek.

So there I was in my shop making some simple trivets by cutting a series of 1/4" dados in a square pice of wood. I'm using a Sawstop contractor's saw that I purchased a few months ago. I'd made a jig to hold the workpiece with a hold-down attached with a couple of screws. I completed one side of the project, flipped the piece over and rotated 90 degrees to do the other side (which generally results in a nice gridwork pattern) and was about halfway through when my saw popped and the blade vanished. bewildered at first, I figured out pretty quick that the brake had triggered for some reason. Since my fingeres were nowhere near the blade, it must have hit some metal in the wood...... I examined the workpiece and checked it again with a metal detector - no metal. I then realized that the dado blade must have hit the screws for the hold-down, checked the bottom of the jig, and sure enough - I could see evidence of two separate screws that had been hit on consecutive cuts. (DOH!!) But wait a minute - that means the brake DIDN't fire when it hit the first screw! How come? Is there a hidden sensitivity adjustment? I'm attaching pictures of the jig and the setup I used - as you can see there is a screw visible in the 4th and 5th dados from the left. The blade triggered while I was cutting in the 5th slot, but had not yet reached the 4th slot when working this side of the trivet - apparently it had been hit while working on the other side.. Difficult to explain but perhaps the pictures will explain it better. Any ideas why the brake didn't fire when contacting the first screw? (hopefully the sensitivity is better when chewing into fingers - I don't want to lose one finger only to have the saw fire on the second....)

Dave Sharpe

[Kyle Iwamoto]

My GUESS would be that you were touching the hold down clamp when the brake fired. If you were not touching the hold down when the blade cut the first screw, no path for the electricity. Therefore the brake would not fire. Hard to picture how you were cutting and why/when you would hold the clamp. Can you recall?

[Dave Sharpe]

Not certain, but I don't think I was touching the clamp. I beleive I was simply pushing the entire jog through the blade - no reason to touch the clamp in particular. My understanding is that metal or enough moisture in the wood will trigger the brake.

[Dave Sharpe]

Here's the reply (very quick response) from Tom Berkley of Sawstop:

Hi Dave,

Sorry to hear about your recent activation. When you saw through a
nail, staple, brad, or screw, the metal fragments need to get through
the gap between the teeth of the blade and the surface of the brake
cartridge without shorting them together electrically. It depends on
how large the metal fragments are and whether you have your gap adjusted
properly. If the gap is tight, the metal fragments are not going get
through without causing an activation. Sounds like you may have been
lucky the first time and then got caught the next time. The proper gap
should be about 0.070" or the thickness of a nickel. We have been
experimenting with insulting the surface of the brake cartridge with a
strip of packaging tape. This aides in keeping metal fragments from
being a problem. You can try this without any concerns for affecting
the operation of the safety system. Let me know if I have answered your
questions.

Thanks,
Tom

[Don Abele]

So is he saying it fired because the blade shorted out to the brake? That's the way I read it. And it sounds easy enough to fix without affecting the safety mechanism.

How many ways are their to get the brake to fire? And is this brake to blade shorting the same reason that wet wood causes it to fire?

BTW, SawStop should not be insulting their brakes...they are very important to the whole system .

Be well,

Doc

[george wilson]

A friend had an architectural model shop. Several times their saw stop fired off probably because someone contaminated the saw with mirror acrylic sheet,leaving metal particles inside the area of the brake.

[Kyle Iwamoto]

Wow, that is interesting. That could very well be the reason very wet wood would trigger the brake too.

I guess the lesson learned here is to keep the gap on the large side? Do you remember if you set your gap tight? I just changed mine, since the saw didn't start. I set it pretty close........

Or, no offense intended, do not cut screws/staples/brads.

Thanks for the original post and the reply!

[Dave Sharpe]

no offense taken - I made the mistake, I have to pay for the new brake.
I can understand the issue of wet wood causing false triggers, as a buildup of wet sawdust could easily bridge the gap between a spinning blade and a brake set close. It seems that the brake needs to be as close as possible to reduce stopping time in the event of a real activation. I seem to recall that explanation from the owner's manual.
One thing I've noticed when showing off the new saw is that it doesn't always sense a finger touching the blade. For those not familiar with Sawstop, there is a control panel with red and green indicator lights. When the saw is powered up, the control panel runs through various checks before the motor itself can be turned on. In this standby mode, one can touch the non-spinning blade and see a red light flashing to indicate that the saw is sensing the touch. However, I've noticed that a light touch to the tip of a carbide tooth does not always result in a red-light indication, meaning the saw is not sensing at that point. It raises concerns for me that a finger in the blade may not always trigger the brake as quickly as I'd like. i wonder if this is related to the distance between the brake and blade. I'm waiting to hear back from Tom on this question,

Dave

[Paul Ryan]

Dave,

I would check with SS about your finger test. I have tried that on my saw with every blade I use and the electronics pick up my finger very quickly. You may have something funky with your blade or electronics.

[Rob Price]

I think the issue with wet wood is more of a conductive/capacitance issue. You can test wet wood with the blade stopped and it will tell you if it's to wet or not. My understanding is that to trip the break you need to absorb enough of the charge on the blade to meet a threshold. I cut a brad a few weeks ago without a problem. SS said it was because a single nail shouldn't absorb enough charge, unless I was touching it. Is there any chance the offending screw was in contact with the table top or some other metal surface?

Each time I've tested the saw in standbye mode it detects my finger every time. I've even tried very light touches to trick it. If yours doesn't I would be talking to SS about getting the brake/switch/electronics checked out.

[Brian Kincaid]

We have been experimenting with insulting the surface of the brake cartridge with a strip of packaging tape.

Reminds me of the Heiniken commercial where they made the keg small by insulting it with crude Scottish remarks.

Brian

[Daniel Baker2009]

The surface of your fingers are too dry to make a strong enough path for the charge to activate the light. Pressing firmly creates enough contact for the voltage to drop enough to engage the brake. In operation, the blade will slice through the thin dry layer of skin and create a path for the voltage to drop. Nothing wrong with your saw -- just dry hands!l

The little computer inside the brake monitors a 3volt charge and when in 'sees' a significant voltage drop it activates the brake. Your body is a big enough energy sink to activate the brake. I've demo'd the Sawstop and you can cut through a hot dog if you are not touching the dog or the dog is not grounded out on the cast iron table. (Embarrassing demo when using a wooden sled!)

At my work we have a Sawstop and the most important thing we check for is the gap between the blade and the brake. The differences in 10" blades is amazing.

Dan

[Matt Benton]

Anyone with a SS find themselves constantly waiting for the brake to fire? I think that if I owned one, I would be a basketcase just waiting for it to go off due to some electrical anomoly...

[Byron Trantham]

no offense taken - I made the mistake, I have to pay for the new brake.
Dave

How about the dado blade?

[Dave Sharpe]

QOUTED: "I've demo'd the Sawstop and you can cut through a hot dog if you are not touching the dog or the dog is not grounded out on the cast iron table. (Embarrassing demo when using a wooden sled!)"

Interesting! I didn't know about the "energy sink" concept, but I guess that makes sense. Makes me wonder if the inventor wet his hands first before filming that demo where he deliberately stuck his finger in the spinning blade.