Shopsmith Forums

edma194 wrote: ↑Thu Jan 25, 2024 4:32 pm According to Scott Markwood rapidly stopping a Shopsmith blade was tested for some reason, not necessarily for this purpose, and they found that the torque could tip the saw over.

The reason was that SawStop was lobbying -- "in the interest of safety" -- that every table saw maker would have to license and utilize their patented blade brake. They were doing so "solely out of concern for the protection of woodworkers' -- I'm sure all those patent royalties they would receive had nothing to do with it.

As he told the story, ShopSmith was experimenting with how a blade brake would perform on a Mark and found that when they stopped the blade cold the machine flipped over.

He also contrasted that with ShopSmith's handling of their patent rights to the feather boards and push blocks they designed. In the interest of woodworkers' safety, they licensed the designs to other companies for free!

I don't see how the blade on a Mark could be dropped below the table. Instead the table would have to pop up to cover the blade. This would also fling anything on the table up and potentially directly at the operator.

Drop the headstaock!

HopefulSSer wrote: ↑Thu Jan 25, 2024 9:56 pm The reason was that SawStop was lobbying -- "in the interest of safety" -- that every table saw maker would have to license and utilize their patented blade brake. They were doing so "solely out of concern for the protection of woodworkers' -- I'm sure all those patent royalties they would receive had nothing to do with it.

I agree, but in fairness I think we can also assume that those lobbying against adopting a new table saw safety requirement also had (or have) a profit motive for opposing it. And they've been pretty successful, CPSC has been working on this on and off for over 20 years.

IMO the rule itself is lame. 1 meter per second surrogate probe movement and a cut depth limit of 3.5 mm? That protects people that feed themselves into the blade along with the wood, some percentage of table saw accidents I'm sure. But the violent incidents like kickbacks that injure some are going to produce velocities significantly greater than this. The CPSC's analysis of a linear relationship between feed rate and degree of human damage is flawed by relying on only one technology and a sample of one. (Sawstop, of course.) And can the manufacturer's presume that other safety equipment, riving knife for example, is present per the instructions in the manual? I didn't see where it addressed this.

- David

DLB wrote: ↑Fri Jan 26, 2024 9:40 am I agree, but in fairness I think we can also assume that those lobbying against adopting a new table saw safety requirement also had (or have) a profit motive for opposing it. And they've been pretty successful, CPSC has been working on this on and off for over 20 years.

Exactly. I just hope we (forum members) aren't embracing the status quo out of fear of change. I don't think any of us like added safety features that can be a nuisance - hold bar on push mowers for instance. However, when these new safety features save your butt, you are glad they are there. Imagine where we would be today without innovations like seatbelts as but one example. There are countless others. I really don't care whether it is a SawStop innovation or some other company's ingenuity that saves the day. I just know a future with more safety features on woodworking tools is a better future. Hopefully they are more akin to the adding seatbelts variety and less akin to the push mower hold bar type of changes.

RFGuy wrote: ↑Thu Jan 25, 2024 5:10 pm Ed,

Sounds like an urban myth to me!!!

Don't know why you would doubt this would happen. The rotors in both the induction motor and the PowerPro must weigh around 25 pounds or more and moving at 3500 RPM on the induction motor or thereabouts when sawing with the PowerPro. That's a tremendous amount of momentum which is going to move the machine if it's stopped in 10ms. I suspect the SawStop originally looked at the brake alone and discovered the momentum was a problem requiring the entire motor and blade assembly to drop into the table so it doesn't flip the saw over.


There's no way those motors can electrically brake in 10ms and more than they could run up from 0-3500RPM in 10ms.

And for those doubters, take a saw blade and look at your machine. A 10" blade will fit completely under the table at it's lowest height in table saw mode (maximum blade height above table). It's tight, you need an 1/8" of material for the lower saw guard between the blade and the way tubes and you need the space between the way tubes to get the blade all the way down that far. At worst you might need to limit blade height slightly when the safety system is activated.

edma194 wrote: ↑Fri Jan 26, 2024 9:57 am Don't know why you would doubt this would happen.

Because I don't believe everything I read on the internet or see on someone's YT channel.

If kickback is the cause of significant numbers of severe injuries, they should outlaw push STICKS or mandate hold DOWNS.

Blade dropping solutions ignore the arbor etc. on a SS.

RFGuy wrote: ↑Fri Jan 26, 2024 10:01 am

edma194 wrote: ↑Fri Jan 26, 2024 9:57 am Don't know why you would doubt this would happen.

Because I don't believe everything I read on the internet or see on someone's YT channel.

So you don't believe in momentum? Any other physical properties of the universe you think are urban myths?

RFGuy wrote: ↑Fri Jan 26, 2024 10:01 am

edma194 wrote: ↑Fri Jan 26, 2024 9:57 am Don't know why you would doubt this would happen.

Because I don't believe everything I read on the internet or see on someone's YT channel.

There really is fake stuff out there?

JPG wrote: ↑Thu Jan 25, 2024 11:08 pm Drop the headstaock!

Instead of stopping or retracting the blade, maybe SS could go with the impenetrable-guarding approach. This RAS at my local Big Orange could serve as an inspiration. It even limits the universe of RAS operations to the only one approved by Stumpy Nubs!


If you put a guard like this on the SS table, you might not be able to rip, but at least you could still crosscut boards (by lowering the table and workpiece down onto the blade)!