Would you buy this safety device?

[Charles Krieger]

Assume I could engineer and build a safety device that would create a safety zone around the danger, ie saw blade or other cutter. If ones body parts entered into the safety zone an alarm would sound and the device would shut down. No braking would be provided so danger still is present from the spinning blade/cutter. The safety zone could be set to the 3" rule or other specified distance. The alarm would possibly give the operator time to stop/pull back and in a commercial shop it would alert management to safety zone intrusions by employees.

This device could conceivably be added to most any stationary power cutting tool.

What if anything would such a device be worth?

[Brian Clevenger]

What if anything would such a device be worth?

Perhaps a finger or two.

[Frank Hagan]

I'd check with an attorney on this one. Because the "state of the art" for cutting tools is now a blade brake that prevents serious injuries, a proximity alarm that still allows injury may open you up to liability. Especially if the worker claims the alarm startled him, forcing him to jam his hand into the still spinning blade.

The problem is that you have to know how it would be dealt with in all 50 states for the US; we don't have uniform liability laws, but have 50 individual jurisdictions.

Your device might allow a different kind of blade brake to be used that doesn't require paying royalties to the current Sawstop patent holder and doesn't destroy the blade and braking mechanism, so it could still have some appeal to equipment manufacturers. They might be interested (and they have a handle on that liability problem already). It might also be of use in other trades to ensure only authorized people use machines (by means of an identifying RFID chip on a glove, for instance). Or for machines like punches and presses that can stop without having the momentum of a spinning blade (I can see it for those large sheet metal brakes and presses).

[Peter Quinn]

Would I buy it? No, I would not. It seems to give the appearance or feeling of safety with out providing any actual safety. Brakes, hold downs, power feeders, guards, splitters or riving knives, these things provide actual safety and stock control. I prefer not to be startled by loud noises in the shop when I am wearing head phones and focusing on not cutting off a finger, and for an alarm to be useful it would have to be loud.

[Art Mulder]

What if anything would such a device be worth?

I don't think there is one answer to this. It's a sliding scale.

If the premium is the same as the sawstop, then I think you can expect a similar-sized market (though there are other good design features on those saws).

If the premium is more, then you can expect a smaller market.
If the premium is substantially less, then you can expect a bigger market.

I'd aim for the $100 price point. It's not a huge amount, and something that many folks would probably be willing to shell out.

...art

ps: but I wonder about that guy with the "startle" comment. Seems plausible. I think I might prefer if it just shut the machine off without an alarm. Or maybe just a blinking light to go with the shut down.

[Anthony Whitesell]

The device is called (or nicknamed) a light curtain and they are current available and in use on all kinds of automated machinery. It would just be a matter of adapting one for this purpose.

[Chris Parks]

I don't see how a light curtain would work. As soon as you push a bit of wood up to the blade it would go off, or so it would seem to me. Now if you used an Infra Red Sensor that would work but I still wouldn't buy one for lots of reasons.

[Anthony Whitesell]

For any type of soft curtain (versus a hard blade guard) the problem would be mounting it and allowing for clearance for the workpiece to be fed through the blade. I have a few ideas for mounting options but I'm not putting to much thought into it. A good blade guard is the best and the second option would be a blade brake.

What is really too bad about the Sawstop is that it braking works using the actual blade and not a sacrficial blade/gear/ring/etc. also mounted on the arbor.

[Don Bullock]

...
What is really too bad about the Sawstop is that it braking works using the actual blade and not a sacrficial blade/gear/ring/etc. also mounted on the arbor.

Anthony, you have a super idea there. Perhaps some company out there might jump on it and produce such a system. It could work on just about any woodworking machine.

[Anthony Whitesell]

After thinking about it a little more (and for the company that snooping here for ideas), I think the arbor nut would need to be redesigned. If the nut tightens in the direction of the load (tightens clockwise, spins CCW, load would be CW), If the shaft stopped suddenly, then the load from the spinning blade may try to loosen the nut. I'm just a mechanically inclined EE and maybe an actaul ME would have a solution.

[Matt Meiser]

Anthony, I've heard that problem mentioned as a possibility when someone uses a VFD on a table saw. Maybe a solution could be as simple as adding a small pin on the arbor that engages a hole in the blade. This seems like a modification that could be made to the blade even at home. They could just supply a small jig that has a drill bushing? If its was even an issue, they could have you drill two holes exactly opposite each other to prevent affecting balance.

On the original question, I would have to vote no for many of the reasons already stated. Just shutting down power wouldn't have prevented the accident I had with a router. And I think any effectiveness would be entirely dependent on the installation.

I've worked around equipment with light curtains. I'm not a safety expert, but thinking back it seems like they are usually placed far enough back that you couldn't get to anything dangerous before its danger is reduced or eliminated. And fast moving things--even things like robots that can be stopped in a lot less time than a spinning blade--are protected by gates. Some of the gates even have electromagnetic locks that engage when the equipment is in auto.

[Tony Bilello]

A zone alarm can be a distraction. What if you are making an unusual cut and start outside the zone ( no lalrm) then you enter the zone and have an alarm when you are partly into your cut? Lots of different scenarios there. Also, if you make difficult but samfe cuts with a jig it may be such that it would set off the zone alarm. So, you disable the alarm for these cuts, then the next cuts and after a while, you never use it.

[Glenn Howard]

How will this device distinguish a body part from the work piece? Without a method similar to the Saw Stop (which requires touch) I don't see how it could.

Without a brake, I doubt an alarm sounding if you get within 3 inches of the blade would do much more than startle you into moving ahead the other 3 inches.

The success of the Saw Stop is that the brake device is able to react more quickly than the human brain. This "danger zone" method still depends on the relatively slow reaction ability of the human brain.

Saw Stop got it right. Now if they're really smart, they're spending their R&D time while the patent is still in effect working on an aftermarket version that can be adapted to other brands of saws. And if they just got this idea from me, I'll expect a cut.

[Mark Elmer]

I'm in the not likely to buy group on this one too. My father taught me not to fear tools but to be sure that I respect them and what they can do both good and bad. I keep factory safety equipment in place if at all possible too.

I'd rather take the money that an "alarm" would cost and buy something that creates a barrier against contact with dangerous blade. An overhead blade guard is on my short list of safety upgrades for my tablesaw.

[Shawn Buonarosa]

I suspect that the vast majority of WW accidents happen so fast, that no matter what kind of audible alarm went off there would no chance to stop it.
So to answer the question, no I would not buy this.