How important is a riving knife?

[jonmnelson]

Couple questions --

1. I know new saws will be coming with riving knives at some point, but I'm wondering how much important riving knives are. Are splitters that much less effective? Has anyone bought one saw over another -- even if they weren't necessarily comparable -- strictly because of the riving knife?

2. Is the riving knife on the BT3X00/21829 really a riving knife? Most riving knives I've seen stay just below the height of the blade, enabling the user to make non-through cuts without having to remove it. The riving knife on the BT3X00/21829 seems to be more like a splitter that rides up and down with the blade and obviously has to be removed for non-through cuts.

[DonHo]

I'm not an expert but I believe that in theory a riving knife and spliter would be about equal in preventing kickback. But in practice riving knives are better because they are used more, at least the one on the BT3 and 21289. A riving knife moves with the blade and a spliter doesn't and in many cases because of how they attach to the saw spliters are farther from the blade making them less effective. I don't know if being higher than the blade makes it a spliter or not but for the BT3 and 21289 you can replace the stock blade guard/knife with a Sharkguard. If possible this is a good way to go. In my opinion it's much safer because it makes much more easy to remove/replace the blade guard, it is lower than the blade so you can leave the knife on the saw for non thru cuts(not dados) and therefore you are much more likely to use it (none of them will protect you if you aren't using them).

Just my 2 cents,
DonHo

[LCHIEN]

Couple questions --

...

2. Is the riving knife on the BT3X00/21829 really a riving knife? Most riving knives I've seen stay just below the height of the blade, enabling the user to make non-through cuts without having to remove it. The riving knife on the BT3X00/21829 seems to be more like a splitter that rides up and down with the blade and obviously has to be removed for non-through cuts.

Look at the Sharkguard, this replaces the BT3x/21829 blade guard assembly and provides the function you describe - top of knife below the blade top. It also provides a way to fasten its blade guard to the top of the riving knife and thereby solves a safety issue - ease of replacing the guard before and after non thru cuts. It's described more in the FAQ I sent you...

[LarryG]

My understanding is that a splitter is attached to the table and doesn't move, whereas a riving knife moves up and down with the blade and hugs it closely in order to provide the same degree of kickback protection regardless of cutting height. With a splitter, there can be a considerable gap between the blade and the leading edge of the splitter at a low blade height.

I think Keith (drumpriest) will tell you that the inclusion of a riving knife is the specific reason he chose a Powermatic 2000 when he upgraded to a cabinet saw. I can tell you that it was certainly a factor in my decision to purchase the same saw, but not necessarily the factor. It was pretty important, though.

I replaced the stock splitter with one of Lee's shorty models, so the RK can stay on for all cuts. I don't use a blade guard.

[Jeffrey Schronce]

If I ever had to pay full retail for a saw (oh the horror!) and was looking at cabinet saws, I would choose the Powermatic PM2000 with a good portion of that decision tied to the riving knife, built in mobile base and fit and finish. Having said that, I purchased a Delta Unisaw X5 5 hp unit with 52" Bies fence for half of retail for PM2000. After seeing the Shark Guard installed on my old 22124 by the new owner, I immediately ordered one. I can't see how this thing could be any better or safer. It is just awesome. The SG comes with non-full height splitters for doing non-through cuts. The SG, ZCI and proper alignment make my Unisaw a very safe saw. I do use a blade guard anytime I am doing a through cut except extreme angles which has presented a problem with the SG ratcheting arm and my throat plate.

Conclusion : Shark guards rock.

[jonmnelson]

I'm not an expert but I believe that in theory a riving knife and spliter would be about equal in preventing kickback. But in practice riving knives are better because they are used more, at least the one on the BT3 and 21289. A riving knife moves with the blade and a spliter doesn't and in many cases because of how they attach to the saw spliters are farther from the blade making them less effective. I don't know if being higher than the blade makes it a spliter or not but for the BT3 and 21289 you can replace the stock blade guard/knife with a Sharkguard. If possible this is a good way to go. In my opinion it's much safer because it makes much more easy to remove/replace the blade guard, it is lower than the blade so you can leave the knife on the saw for non thru cuts(not dados) and therefore you are much more likely to use it (none of them will protect you if you aren't using them).

Just my 2 cents,
DonHo

Why couldn't you leave the riving knife on for dados? If it's the type that is no higher than the blade, it doesn't seem it would interfere with the dado cut, although I guess it wouldn't serve much of a purpose when cutting dados.

[Uncle Cracker]

Why couldn't you leave the riving knife on for dados? If it's the type that is no higher than the blade, it doesn't seem it would interfere with the dado cut, although I guess it wouldn't serve much of a purpose when cutting dados.

Because most dado sets are 8" or 6" diameter, so the riving knife, which is set for a full 10" blade, actually would sit up much higher than the dado blade, thus preventing a through cut.

[Knottscott]

A riving knife is a more elegant design solution to keeping the workpiece from closing up and binding on the blade, but a splitter is also effective when properly aligned and in place. It's hard to gauge how much more effective the RK is than a splitter in it's most basic function in actual use. All the theoretical advantages favor the RK, but when properly installed, both systems are capable of preventing the kerf from closing. The RK tends to be in closer proximity to the blade, but most reactionary wood won't close the gap for several inches past the exit side of the blade, and any splitter I've seen is within close enough proximity to do the job. The ability to raise and lower with the blade is a function that the splitter can't do at all, and is a leading reason for leaving the splitter off for some tasks, which brings us back to the primary benefit of the RK...you're more likely to have it place when needed. I've read a lot and thought about the differences between the two, but haven't yet experienced any revelations or insights that allow me to view the RK as much more than an improvement...it's not a technology breakthrough that significantly changes the safety of the process, but it does reduce our tendency to not practice prevention.

IMO, it's important to have one or the other in place and properly setup. I view a splitter or RK to be more important than the blade guard, but that's just my opinion. I think I'd enjoy having a riving knife on my saw, but I don't view as important enough to warrant paying a significant premium for it.

[eezlock]

how important is a riving knife?

I think a true riving knife like the BT3 saws use is a very important feature
especially when doing a lot of ripping of stock. The replacement type like the Sharkguard are a huge upgrade to the saw, they should be used on any saw
and I feel like that eventually the Sharkguard type will be the choice for all new saw owners who are concerned about their safety. Lee will probably busy designing new ones for older saws for a long while to come! eezlock

[crokett]

A safety feature is not effective if it is not used. So says the guy who runs his saw with no guard. That needs to be factored into any decision regarding the advantages of a riving knife over a splitter. Being forced to take the splitter off more often means it probably won't be used as much.

[niki]

As you know, the riving knife is mandatory on all the EU saws (also on the imported from Chiwan). The Anti-kickback pawls are not mandatory.

But, the riving knife is half of the story...a riving knife should be used with "short fence" as posted by SARGE some time ago.

The riving knife is not only moving up/down with the blade (and stays at the same reference to the blade) but also tilts with the blade so there is no need to remove it for any cut (it sits just below the blade).

The guard is installed on the riving knife just with a "click" and wing nut so it encourage the operator to use the guard (and I do "waste" the 3 seconds and install it)

If you are using a dado blade (I don't) you can remove the riving knife (one nut) at the time that you change to dado blade and re-install it when you change back to normal blade.

On the pic, you can see my riving knife and the guard that clicks into the slot at the top of the riving knife....I did not remove the riving knife since I bought the saw...

Regards
niki





BTW, for all the "No Guard" lovers.
I touched the guard by mistake without any connection to the cutting operation...if the guard was not there, you would see very "red" picture (and a post about accident) but, it was there...

[LCHIEN]

Niki, EU rules no longer permit Dado blades, right? Not specifically, but basically all new EU table saws have short arbors (limited by law) so that they cannot take a Dado, essentially.

[niki]

Hi Loring

Long time ago it was forbidden to use dado blade and all the arbors were made short...

A few years ago, they got permission to use dado blade up to 15 mm (19/32") and don't ask my why...

Lately, I read that they got permission to use dado blade up to 19 mm (3/4").

I think that it's just confinement for the makers to continue to make the short arbor.

The regulation is "Blade guard must be installed for any operation"....they "override" this limit buy using the Over Head guard that is acceptable according to the safety regulations.

Regards
niki