Hacker News Reader

Comment by jtriangle | Hacker News Reader

No, I mean they had table saw rigs that would bring the saw up/down into the floor with an actuator as a 'ring hazard', ie, your robot could be subject to sawing at any moment if they happened to be there.

The question is, how fast does it need to be? Likely not that fast really, certainly not microseconds, and an actuator could easily yank the saw down without damaging it if it detected you were about to lose a finger.

There's also no reason you couldn't use the same actuator to do fancy things, like vary cut depth on the fly, or precisely set the cut depth in the first place. Can't do any of that with a soft aluminum pad that gets yeeted into the sawblade when it detects a problem.

Basically, SawStop exists to sell saws. Those saws happen to be safer, but that's a marketing point, it's not what ultimately makes them money. Look at the incentives, you'll find the truth.

View on HN

>The question is, how fast does it need to be?

I don't know - the marketing material actually says 5 milliseconds. That's the crux of the problem and I don't believe you can actually move the saw fast enough to not cause serious damage to the human without damaging the saw. The problem, as I understand it, is stopping the saw. The saw actuator only makes sense if it moves fast enough and given the saw stop works on detection, I'm not convinced you have that much time.

I'm considering the physical reality here - if the saw must be yanked down quickly, how much force must be applied to the saw to move it, and then can that equal and opposite force be applied to stop it without damaging the saw?

>Look at the incentives, you'll find the truth.

This is true of any safety device? The SawStop inventor created his company after trying to license it and eventually won in the marketplace after nearly 30 years. Surely his competitors would have released an actuator based solution if it is was possible rather than ceding marketshare of high end saws?

Bosch did release an actuator-based solution. They got sued by SawStop for patent violations and lost and pulled it from the market. SawStop's main patent just covers the concept of a blade brake, not a specific implementation.

The actual contention isn't whether an actuator-based solution would work, its if an actuator-based solution could stop the saw without damaging it (and therefore not give credence to the claim that SawStop is intentionally designing a poor solution in order to sell more blades).

As far as I can tell, REAXX also damages the blade.

REAXX retracts the blade inside the table and lets it coast to a stop. It does not damage the blade.

>and therefore not give credence to the claim that SawStop is intentionally designing a poor solution in order to sell more blades

This is the most asinine argument I’ve heard yet, and I am not a fan of this regulation.

Blades are typically cheap and the ones that aren’t are often repairable after an activation. Also, Sawstop barely sells any blades - I don’t know a single woodworker or cabinet shop that runs their blades.

I think the speed that things can go wrong when using a table saw (or most power tools) is faster than some people, including some woodworkers, might expect. There's a good example video here (warning, shows a very minor injury):

https://www.reddit.com/r/Carpentry/comments/11s6zlr/cutting_...

While we're still not talking microseconds, I think it highlights that moving the blade out of the way needs to happen very quickly in some cases to avoid serious injury.

Sounds like you're perfectly positioned to start a SawStop competitor!

"Protect your equipment AND your fingers."

With the government potentially mandating these types of devices, you could be makin' the big bucks!

These incentives are clear, where's the truth?

(This is only somewhat facetious. I'm skeptical of your claims, but not enough to discount them out-of-hand. The industry honestly does seem ripe for disruption.)

> The question is, how fast does it need to be?

According to my calculations, on a 10in/ 30tpi blade you have a teeth passing every 8.3uS.

I think the other key variable is how fast is your finger being advanced towards the saw blade and how much total depth of contact are you willing to accept and claim a victory. In an aggressive ripping the material you're holding towards the blade that might be 10 mph (~15 feet per second), if you're willing to tolerate a 1/16" depth of injury, you have about a half a millisecond.

If the rate of advancement is much slower (like a normal pace of feeding the stock into the saw accident), you have several milliseconds before reaching a 1/16" depth of injury from first contact to last contact.

Bosch used to have a system called Reaxx that could pull the saw out of the way without damaging it.

Reply on news.ycombinator.com