Question about riving knife.

[Knottscott]

I'm pretty sure it rhymes with "tomato."

...that's tom"ah"to....

[drumpriest]

Interesting, I've heard people pronounce it both ways before. I'm not sure which is proper, but if Lee says rIving knife, then that's what I'll say, as he made mine.

[wassaw998]

Not to sounds argumentative, but, who has any data that supports any stats on table saw kick backs which shows that the given kick back that occured with a splitter installed would have been prevented had a riving knife been installed? Or, even, a comparrison of kick backs with a splitter installed, versus, kick backs with a riving knife? The distance gained to me is way too small to make much of an advantage, by the time the kerf begins to close (if is it going to close at all), seems either a splitter or a riving knife would be there to keep the gap open and accomplish the task both were designed for. I've seen so many comments that a "riving knife is safer" , but, sorry, I don't see any stats to back them up.

[LarryG]

Chris, like you I am a skeptic about the real-world differences, at least for cuts with the blade perpendicular. I do, however, see an advantage for the riving knife on bevel cuts, since it tilts with the blade and an ordinary splitter does not.

[drumpriest]

Chris and Larry, I don't think that a riving knife is inherantly safer than a splitter and a guard except for the fact that it is more likely to stay on the saw. People tend to take off the splitter and guard assembly the first time that they need to make a non-through cut, and it never gets put back on. The reason is simply that it's a pain in the behind to take on and off.

A system like that Shark is a breeze, I can remove the guard and clamp, leaving only the riving knife, in about 10 seconds. About the same amount of time to reinstall it. There is no reason to take it off for any cuts made with a 10" blade. Mine only comes off for Dado cuts.

That is the biggest safety advantage to me. There is the fact that it can get closer to the blade, which does help the quality of the cuts, IMO. As you are less likely to have the piece wander slightly at the back and get saw blade marks there during the first section of a long rip cut.

[Stytooner]

Kerf closure is also not the sole source of kickbacks.
You can also have kerf separation which could produce pressure against the blade. Use of a dull blade can also cause kickbacks. Improper stock feeding is also a source. Improper setup as in using both fences to crosscut is bad as well.
A riving knife is a splitter, but a splitter isn't necessarily a riving knife.
A well designed riving knife has the advantage of staying in place most all the time. This in itself does make it safer than standard splitters.
The shear proximately of the knife means its sooner effective than a splitter.
Splitters can be so varied in material, mounting and function, that there will be not steadfast statistics other than common sense and logic. Some splitters are only throat plate mounted. Some factory splitters are only mounted behind the rear fence. Side pressure from the fence on these splitters are not hindered at all. Not much of a safety device there.

The typical cases of injury that I have read about mostly sum up to say that a splitter or guard would probably have prevented or lessened the injury. Those statements right there tell me that had a riving knife design been implemented at the factory, the report would never have been filed. There would likely have been a riving knife in place simply because they are far less intrusive to different setups and cuts. More of a passive safety device than a hindrance. Kinda like anti-lock brakes.
You rarely know you have them, but they are there when needed.
I've been around saws long enough and seen and heard about enough injuries to know that the riving knife is simply a more advanced design than the ones invented early last century.
You'll likely never see too many statistics where a riving knife was present on the saw.

[dwolsten]

What I want to know is why the saw manufacturers haven't just put riving knives in all their saws by now. It's actually required by law in Europe as someone else pointed out. And this really doesn't seem like it'd be an expensive thing to add, not like the SawStop system: it's just a simple piece of metal.

There was a debate on another forum about this a couple months ago, and patents came up, but I think that's wrong too since the BT3100 is dirt cheap and still has a riving knife; if Ryobi can afford it on a $300 saw, Delta can certainly afford it on a Unisaw.

[Bruce Cohen]

haha - live or live.

Eye! (to the first question)
Aye! (to the second question)

English. so much fun...

Loring,
Is that pronunced the same in Mandarin or Cantonese??

Sorry, I just couldnt resist

Bruce

[Stytooner]

Bruce, was that a ribbing knife?

[drumpriest]

Dwolsten, you are preaching to the chior, so to speak. I fully agree with you, and in fact find it insulting that it is difficult to find a saw in the US with a riving knife. Laguna and the Powermatic 2000 have them, as well as sawstop, and all of these are fairly expensive tools. I havn't yet seen a hybrid 1 3/4 hp saw with a riving knife, which rules them right out for me when I eventually step up from the BT.

Greed is the only answer, these tools are being stamped out in china where the setup is made for splitters and guards. Perhaps also they have many made and are awaiting their use before any redesign.

[LarryG]

Greed is the only answer

That is very likely correct. A close friend has a BIL who used to work as a design engineer for a large, well-known manufacturer of musical equipment. The BIL told my friend stories of how they'd get a new product into production and then spend endless manhours looking for ways to subtly alter the design to save as little as two or three CENTS on each unit produced. Or even ONE cent. I guess even a savings that small, multiplied by the number of units produced, and extended across the entire product line, added up to a pretty nice executive jet.

Another element might be the potential for liability lawsuits from owners of the older models. I've heard of this factor for other type products and don't know how real the problem is, but simple logic suggests it might be a powerful disincentive to improve an existing design. If a mfr were to suddenly start placing ads that proclaimed, "Now with riving knife, for greater operator safety!" -- that would kinda put them in a tough spot WRT all the older models that are out there already.

[drumpriest]

Yes, but then there would be no growth of technology. Oh wait, that is exactly what has been happening over the past 50 years in the auto industry. There seems something fundementally wrong with our relying upon "market forces" to drive industry. The better design does not always win out, and in fact the larger companies become, the less likely that a little guy with a new and better idea will prevail.

This is getting dangerously close to a political debate though, so I'll end it now so as to not upset Sam. I just think a little thing like my fingers should be a big enough motivation for a large company to make a simple inexpensive change. I know better, but it'd be nice to think better of people.

[Bruce Cohen]

Ribbing Knife???

Hey Lee,

Are you talking about what us Yankees use to cut our Barbeque apart (the other tool used in combination is a ribbing fork, or is it the special knife we use exclusively for a specific type of steak?

Barbecueless in NY

Bruce