Riving Knife - Am I missing something?

[Peter Bucy]

The recent interest in riving knives on table saws has raised quite a bit of interest among woodworker that I know. One fellow is selling his two-year-old cabinet saw to get a new one with a riving knife. Another friend is almost distraught that he bought a new Grizzly cabinet saw last year and now that same model has a riving knife in 2010. While I have always been a strong proponent of shop safety; I have never seen anything like the riving knife phenomenon, at least not with woodworking tools.

I have used a table saw that has a riving knife on many occasions. There is certainly nothing wrong with it; the saw worked fine. But there seems to be a misunderstanding that table saws with a riving knife cannot generate a forceful kickback. They can; I have seen it happen.

Other than being closer to the blade than most traditional splitters, there isn’t much that a riving knife can do that a splitter can’t do. The primary difference is that a riving knife can keep a board that is rising from the table from catching the top teeth of the blade as easily as with a splitter or with nothing at all. If you are working with a table saw where you have not made provisions to keep your work from climbing up the blade, you probably need to address that deficiency rather than count on a riving knife to do the job for you.

Most of the serious kickbacks that I have witnessed over the years have been predictable. The most common was where someone was trying to rip stock that had an uneven edge that caused the board to bind between the blade and the fence. Jointing the stock first, or in rougher wood, running it through a band saw then jointing it would remedy this problem.

Another problem arises when twisted or cupped stock is put on a table saw. The stock either binds with the blade and the fence, or it wobbles on the twist or cup and just binds with the blade on its own. Flattening this material on a jointer first would be the best idea and sometimes a piece of wood is just too defective to safely cut it on a table saw.

I have seen improperly aligned fences that actually punch the piece of wood between the fence and the blade. One of my trim carpenters bought a five-year-old cabinet saw a while back. The guy who sold it to him had never adjusted the fence and the blade. He was very dissatisfied with the saw and sold it. It took me and my carpenter about an hour to get the saw tuned up with the correct settings.

Thin kerf saw blades are another kickback source. Their thin kerf makes binding all that much easier and they tend to warp easier from the heat. When they first came out my carpenters all used them in their circular hand saws. That didn’t last long. They had a tendency to kickback and warp. It didn’t take long for most of the guy to go back to heavier kerf blades.

A big contributor to kickbacks, in my humble experience, has been dull saw blades and saw blades that need to be cleaned. Ripping resinous wood, like southern yellow pine, can gum up a good blade in short order making it more likely to bind to your work.
Other options to reduce kickbacks include anti-kickback style blades. We had excellent results from the blades in both hand held circular saw and job site table saws. Some of my carpenters would not use any other type of blade. Various feather-boards, do a great job of keeping your work from rising up on the blade. Roller type board buddies work well too and they do a respectable job of holding your work against the fence. I have a few Grip-Tite magnetic feather-boards that hold the world against the fence and keep it from rising on the blade too.

I agree with most woodworkers that a riving knife is going to make woodworking safer, but not if we perceive that technology as a panacea and ignore time tested table saw safety measures.

Or am I missing something?

Pete

[jim gossage]

Your're right that riving knives don't save us from misuse of the table saw. One thing they do that a traditional splitter does not do is allow you to make non-through cuts with them in place.

[Jim O'Dell]

No, I think you have it all right. But most of us take the factory splitter off for a specific cut, then leave it off because they are usually very cumbersome and hard to install. The snap in splitters would not be in that group. But then they don't tilt with the blade, so get pulled and the factory unit still not put back on. The true riving knife only needs to come off for daddo work. Regular blade and non-through cuts, it stays on the saw. And if your saw has a quick release true riving knife, something I knew I wanted on a new saw when I got one, makes putting it on as easy as taking it off to do that daddo. It's not so much that it is the end all/be all for table saw safety, but that it will be used much more consistantly.
My Ridgid contractor saw has one of the better splitter/guards available. Easy on and off, tilts great with blade. But because of where it mounts, it makes it hard to design an outfeed table that will work with it. Therefore, mine hasn't been on the saw in 3 years. That is dangerous. I won't have that problem with my new saw. That made the difference in price from the close out of the old style 1023 to the new 691 a no-brainer for me. There are obviously others here that didn't feel as strongly about that as I do. Not a knock on them. We all have our priorities, likes and dislikes. Jim.

[Mike Henderson]

The advantage of a riving knife is that it stays on the saw. Many older saws are operated without any splitter because putting it on and taking it off is so much trouble that the woodworker stops using it. And a safety device that's not on the saw is of little value.

Now that saw manufacturers are making saws with riving knives, if you're going to buy a new saw my advice is to make sure it has a riving knife.

Mike

[Shawn Christ]

I jumped on the Grizzly G1023 closeout at $795 in early December. It bothers me slightly that it doesn't have a riving knife, but neither did the cheapie table saw I was using before. I may add a bolt on ripping knife (****) in the future, but for now it's all my tool fund could afford. The 1023 took me from a 15 amp lightweight to a 3 HP heavyweight, and it's a heck of a saw at that price.

[Bob Borzelleri]

My splitter stays on for all cuts except dado cuts. It's not a big deal to remove and install it depending upon conditions. All it takes is a little bit of time and time is pretty much worth any and all of my fingers.:)

[Peter Bucy]

I jumped on the Grizzly G1023 closeout at $795 in early December. It bothers me slightly that it doesn't have a riving knife, but neither did the cheapie table saw I was using before. I may add a bolt on ripping knife (****) in the future, but for now it's all my tool fund could afford. The 1023 took me from a 15 amp lightweight to a 3 HP heavyweight, and it's a heck of a saw at that price.

I had been looking at a Shark Guard for my 1022Z before I bought the new 1023. It includes a guard with a vacuum attachment and several splitters. You can buy the splitters in a group of 3, or individually, with or without the guard.

http://www.leestyron.com/sharkguard.php

All of the reviews that I have read about the Shark Guard and its splitters were very good. I'm going to order one of my new 1023 and if it works out a good as it seems to be, I'll buy one for my 1022Z if I decide not to sell it.

Pete

[Peter Bucy]

My splitter stays on for all cuts except dado cuts. It's not a big deal to remove and install it depending upon conditions. All it takes is a little bit of time and time is pretty much worth any and all of my fingers.:)

Keeping a guard/splitter on a job-site table saw has always been a losing proposition. Trim carpenters just don't want to take the time to deal with taking them on an off. An improperly installed guard/splitter can cause more problems than it solves too. Instead of trying to enforce a safety rule that will be abandoned just as soon as I leave a job site, I have instead worked on getting the carpenters to use anti-kickback devices like Board Buddies, magnetic feather-boards, and jigs to reduce kickback threats. Anti-kickback blades help a lot too, as do properly setup outfeed rollers.

With the advent of very high quality miter saws most trim carpenters do not use table saws for making crosscuts. The 12" miters saw that I have in my shop makes almost 100% of all crosscuts. Miter saws are inherently faster, they handle longer stock, and they are more accurate than a table saw, especially for repetitive cuts. I think that they are safer too.

What amazes me is that every one of the trim carpenters that have worked for me in the last ten years or so have all of their fingers. Most are smart enough to keep the blade set so that it just barely clears the top of the wood that they are cutting, though I think that this position presents a great kickback threat, and they are pretty good at using push-sticks instead of putting their hands and fingers at risk.

Several of my friends are very disciplined at using their blade guard/splitters. One just bought a new SawStop saw. Smart man!

Pete

[Alan Bienlein]

I have to agree with Peter on this. I've worked on all types of saws from my ridgid ts 3650 all the way to scmi and altendorf 10hp sliding table saws that had 14" blades. I've seen guys cut fingers off with the gaurd in place and guys cut fingers off because they didn't think about what they were about to do. In all honesty I prefer my ts3650 over those other saws due to the fact that on the higher horsepower saws if some thing were to kick back you can't control it but on my ridgid I can bind the blade and stop it. Yes I still have all my fingers and have been working on tablesaws since I was 14 and I'm now 44.

The new safety devices will help but nothing can replace good old common sense and the ability to think about what your about to do on a machine that can possibly kill you and not bat an eye. I always pay attention to what the material is doing as I cut it so that I can adjust my actions accordingly. If I'm ripping a board and see it start to close up I don't continue cutting. I stop and run it back thru the blade again to open it back up and give the blade more room.

Good example is this past weekend I went over a nieghbors house and he was splitting 2 x 4's in half on his saw. His wife was going to walk up behind him while he was doing this to tell him I was there. I grabbed her by the arm and stopped her and made her wait till he was done and he realized himself that we were there. I'm also very particular about who helps me on a saw if I need assistance.

[Rod Sheridan]

Peter, I find that in a home situation, many people remove the guard from their saw, and of course in most cases the splitter goes with it.

My experience is industry is the opposite, guards were not removed when equipment was operated, since that was an offence that if repeated, resulted in a loss of employment.

I presently have a General 650 cabinet saw, which came with a combined guard/splitter assembly.

I still have the stock guard, it's in the box it came in, and has never been installed on my saw. I added an Excalibur overarm guard and a Merlin removable splitter.

I can run the saw without the splitter for non through cuts, keeping the overarm guard in place.

Obviously a saw with riving knife could keep the riving knife installed for non through cuts, however without an overhead guard, there would be no guard, which is another unacceptable situation.

The Shark Guard, has that major flaw, it cannot be used for non through cuts, so you can't use it for grooving or dado cutting, another unacceptable condition.

The trick is to find a solution that works for all cuts, something that even a riving knife cannot do when the width of the cutter changes. You need different riving knives for different blade kerf/plate thicknesses, likewise you would need different thicknesses for different dado/grooving cutters.

You can see why the Europeans don't normally use dado cutters in table saws, it's very difficult to provide proper guarding.

On a saw like mine (left tilt), with the fence on the right of the blade, a riving knife would have to be the correct width for a dado cutter, (Best) or move to the right as the dado width increase ( second best). I don't know of any saw that has that capability.

All that said however, the worst splitter/guard arrangement is far safer than no protection.

Regards, Rod.

[Rod Sheridan]

The snap in splitters would not be in that group. But then they don't tilt with the blade, so get pulled and the factory unit still not put back on. Jim.

Hi Jim, your statement above is not correct for all snap in splitters.

My Merlin splitter is quick release/snap in, and it tilts with the blade.

I certainly commend your safety approach to the saw. I added an Excalibur guard and Merlin splitter to my saw, I don't have an excuse for ever running the saw without a guard.

Regards, Rod.

[John Coloccia]

From the description the OP gave, I wonder if he's seeing true kick backs. A kickback will pinch the piece between the fence and the blade, flinging it over your left shoulder (if you are lucky) and destroying anything that happens to get in it's way. You seem to be describing the saw rejecting the material and sliding it back towards the operator. Still not pleasant, but not a kickback. Unless you bend a riving knife out if the way, which can happen, it is practically impossible to get a kickback with a riving knife installed. To kickback you have to be able to get to the back and top of the blade. This is much different than a splitter, which gives you free access to the blade especially when it is low.

[Myk Rian]

Obviously a saw with riving knife could keep the riving knife installed for non through cuts, however without an overhead guard, there would be no guard, which is another unacceptable situation.
A splitter can't be used on a non-through cut, especially with a dado blade.


The Shark Guard, has that major flaw, it cannot be used for non through cuts, so you can't use it for grooving or dado cutting, another unacceptable condition.
Why is that an unacceptable condition? No blade guard can protect, because the blade isn't coming through the material. Even making a dado cut, the Shark can still ride on top of the stock. It just won't be doing anything, except being in the way.

[JohnT Fitzgerald]

I'm sure you'll find "fanatics" on either side of the splitter argument. To me, it's an 'opportunity improvement' - a feature that if it's available might be a good option. It's like a lot of things - cars, electronics, etc. There will always be a 'new feature' introduced after you buy that makes you wish you had waited. And if it's a feature you really want, then you'll change your buying decision.

As for the splitter....if it's on and help in some situations, it's a good thing to have IMO. Plus, the fact that I don't need to remove it and replace it when making non-through cuts means I'm more likely to always leave it on. That's also a good thing.

This reminds me of antilock brakes back in the 80's and 90's. I think everyone would say they're a good thing, but back then I knew people that didn't see the need for them - after all, they learned how to pump the brakes to improve stopping. The whole point is moot now because for the most part, they're standard equipment.

[Stan Urbas]

I'm with you on this, Peter. I don't have one on my saw and don't intend to add it on. No need.

I DO have a blade guard, on the other hand. I purchased an Excaliber overhead assembly that drops down to the work being cut and gathers up sawdust at the same time. You can do dados with it in place, or you can lift it up. Or swing it away.

I've never had an accident due to kickback. But I have nipped my fingers a few times. And it was NEVER done with a blade guard in place. I've also "bumped" a blade guard a few times over the years, and saved my hands from further abuse in the process.

OK, confession time over - back to work!

[Matthew Hills]

You can see why the Europeans don't normally use dado cutters in table saws, it's very difficult to provide proper guarding.

How are dadoes commonly cut in Europe?

Matt

[Hugh Jardon]

Surely a riving knife is a better safety proposition for a table saw than a (factory) splitter? It goes up and down with the blade (crucial), is closer to the blade, and can be left in place more frequently than a splitter can. The splitter alignment is more difficult than the riving knife as it its mounting is further from the blade.

I have two saws, one with each type of protection. There is no comparison between the riving knife and the splitter.

It's a bit like having a choice between bare head, steel helmet and kevlar helmet. The steel one will do the job in a basic manner, the kevlar in a much better manner. Bare head is just asking for pain.

[Jim O'Dell]

Hi Jim, your statement above is not correct for all snap in splitters.

My Merlin splitter is quick release/snap in, and it tilts with the blade.

I certainly commend your safety approach to the saw. I added an Excalibur guard and Merlin splitter to my saw, I don't have an excuse for ever running the saw without a guard.

Regards, Rod.


Thanks Rod. I haven't seen the Merlin. All add on splitters I've seen are stationary. Can you post a picture of it? I'd love to see how it attaches! Might be an option several people could/would use. Jim.

[Greg Sznajdruk]

How are dadoes commonly cut in Europe?

Matt
Dado blades are not allowed in Europe, my understanding is that they use dynamic braking to stop the saw blade. Dado have a larger mass and the dynamic braking could back off the arbor nut. Dado are cut using other methods like routers etc.

Greg

[Rod Sheridan]

A splitter can't be used on a non-through cut, especially with a dado blade.


Why is that an unacceptable condition? No blade guard can protect, because the blade isn't coming through the material. Even making a dado cut, the Shark can still ride on top of the stock. It just won't be doing anything, except being in the way.

As I stated a splitter cannot be used for a non through cut, however a riving knife can as it is not higher than the blade.

An overhead guard can be used when cutting a dado, as it is supported from above on an arm.

A Shark guard is supported by the splitter, which has to be removed for a non through cut, so it can't be used.

A guard isn't in the way when making dadoes, it's preventing you from sticking your hand in the dado cutter. Ask anyone who has had an accident with a dado, whether they wished they could turn back the clock and install an overarm guard.

Regards, Rod.

[Rod Sheridan]

Dado blades are not allowed in Europe, my understanding is that they use dynamic braking to stop the saw blade. Dado have a larger mass and the dynamic braking could back off the arbor nut. Dado are cut using other methods like routers etc.

Greg

That's part of the reason, the other is that the saw guard has to be removed, unless it's an overarm guard.

Since you aren't allowed to remove the guard, no dado or rebate capability.

In Europe, there is more of a tendency to use the proper machine for the job, so most small shops have a shaper. A table saw is a poor second cousin compared to a shaper when it comes to rebating, especially once a stock feeder is used.

That said however, I just ordered a Hammer B3 Winner, with dado capability, and yes it has electric blade braking. Dado capability adds about $200 to the cost of the machine.

The dado cutters for the Hammer/Felder machines look like shaper cutters with scoring and hogging cutters. They also are drilled for the two 9.5mm drive pins, that keep them from spinning on the 30mm shaft.

The saw blades for these machines also are bored to accept the two drive pins so they don't unscrew during braking.

Regards, Rod.