Riving Knife Question

[Aaron Beaver]

1.)Can any table saw be outfitted with one?
2.)Do they have pawls attached to them or do you need pawls?
3.)Can you no longer use thin kerf blades with them, didn't know if they came in different thicknesses.

Just inquiring.

[Cory Newman]

I've never seen nor am I aware of an aftermarket riving knife. I don't know how you could retrofit a saw for one if it didn't come with it in the first place.

[Jim Becker]

Due to the fact that a true riving knife must move up and down with the blade, any kind of retrofit would be difficult at best to pull off. In a recent thread, someone made note of somebody that they though was trying to find a solution in that respect.

The good news is that there have been several table saws released recently that incorporate riving knifes in their design. The two best known are the SawStop and the PM2000. There was a piece in a recent issue of Fine Homebuilding that mentioned two "portable" saws that also have riving knives, but I can't seem to find the article right now. (And, of course, there are the Euro sliders $$$) Hopefully, this will be a trend as manufacturers/vendors release new machines. I believe it represents something that is actually "doable" for a reasonable investment...much more so than the nifty braking system in the SawStop.

Oh, you generally CAN retrofit many saws with an aftermarket splitter that is easily and quickly removable. Some of those are compatible with thin-kerf blades. (The Biesemeyer that I use is not...1/8" kerf or larger only)

[Jim O'Dell]

I saw a post somewhere where someone was contemplating building something that would add on to certain saws. It would mount somehow behind the blade. Drawback was to take it off for some reason, the blade would have to come off first. Not sure that would be a problem, or what circustance would require that it not be on the saw for a cut. I don't know of anything currently on the market that will add on, though. I half-heartedly looked at my contractor saw to see if there was a way to do it, but didn't dig deep enough other than to see that my first idea was not going to work. Had other things to do at that point, so left it there.
Not sure either about the different size kerf blades, but I thought that usually the thin kerf were for lower power saws to help them cut the harder/thicker woods. If that is the case, then it's not likely you would need a thin kerf blade on a current saw that comes with the riving knife...they all have power to spare. :D Jim.

edit. Jim, we must have read the same thing!!

[Tim Martin]

I retro fitted a riving knife to my saw which always stays on. It raises/falls and tilts with the blade and is adjustable on all planes to line up with the blade.

Yes it does drop faster than the blade, but there is always enough knife above the table to support through cuts.

Riving knife is not in much use when doing a non-through cut anyway, so its not too much of a problem/

[glenn bradley]

It appears that unless you're very creative and your saw will accept it like Tim's, after market probably isn't around. I can understand this as many makers are faced with rethinking years-old trunnion designs in order to provide riving knives on their new models.

[chad cummings]

Can you post some more pics showing how you attached it to the trunion. I am really interested in doing this to my new JET.

[Steven Wilson]

1.)Can any table saw be outfitted with one?

No, you may be able to fabricate one for your saw but not any table saw can be outfitted with one. The riving knife needs to raise, lower, and tilt with the blade. It also needs to fairly stout if it's going to do any good. You also need to be able to adjust it. For maximum benefit (i.e. avoid kickback) the knife needs to be adjusted to ride very close to the blade.

2.)Do they have pawls attached to them or do you need pawls?

The pawls are a gimic on any table saw, the splitter (or riving knife) is the important part. The pawls might prevent a push back but will not stop kickback. A riving knife properly setup will prevent most kickbacks.

3.)Can you no longer use thin kerf blades with them, didn't know if they came in different thicknesses.

The thickness would depend of the manufacturer. The riving knife on my Minimax CU350 is standard kerf. I don't use think kerf blades - with a 4.8HP motor and 12" blade to work with I don't need thin kerf blades.

[Al Willits]

Not sure if these would be close, but Woodcraft has something called a Merlin splitter and either Woodcraft or Rockler have a little half circle thing that attaches to the insert.

Al

[jeremy levine]

http://www.garymkatz.com/Tool%20Reviews/RivingKnife.htm

This looks like it might point in the right direction

[Howard Acheson]

>> 1.)Can any table saw be outfitted with one?

No, riving knives need to move up and down with the blade.

>> 2.)Do they have pawls attached to them or do you need pawls?

No, because the blade moves up and down, pawls would have to be manualling reset for each change in blade height.

>> 3.)Can you no longer use thin kerf blades with them, didn't know if they came in different thicknesses.

Riving knives are generally a few milimeters thinner than the width of the kerf produced by the blade. Therefore, the kerf produced by thin kerf blades may not be wide enough.

[Jim Becker]

http://www.garymkatz.com/Tool%20Reviews/RivingKnife.htm

This looks like it might point in the right direction

That's one of the saws I referred to in my previous post...it's already setup from the factory for the spitter (and consequently the modified splitter/riving knife) to raise up and down with the blade. Most saws do not currently work this way and a riving knife retrofit is "difficult".

[Bill Boehme]

Riving knives are generally a few milimeters thinner than the width of the kerf produced by the blade. Therefore, the kerf produced by thin kerf blades may not be wide enough.

I think that you meant to say a few thousandths of an inch thinner than the blade. A few millimeters (assuming 3 as a few) would be nearly one-eighth inch thinner.

Bill

[John Gornall]

I have so often heard that a riving knife can't be added to a typical cabinet saw. I wish there was someone with a little mechanical skill that would put this one to rest. A table saw is a simple machine. The blade quadrant only moves a few inches. There are a number of ways to add a riving knife and it wouldn't be difficult or complex.

Look at a cutaway drawing of a Unisaw - there are lots of the old patent drawings on line. The shaft that raises the blade has a worm gear on it that moves the curved rack gear on the quadrant to raise the blade. This shaft is long and ends at the back of the cabinet. Add another worm gear to the shaft and add a second quadrant to move the riving knife similar to the way the blade rises and lowers. A simple pivot and link would keep the riving knife level.

There are a number of ways to accomplish this riving knife movement.

I've been surprised that it hasn't been done.

I won't do it because I'm time focused on projects of my own preference and just don't want to do it.

There are so many machines we use in everyday life that are so far more complicated than a table saw and yet a Retro Riving Knife is just talked about.

[Jim Becker]

John, one of the challenges to adding the riving knife is space....around the blade/arbor mechanics and behind the blade. There isn't a lot to work with and you need to be sure that things don't interfere with other things (hows that for technical terms... :) ) as you raise and lower the blade. Not impossible, but challenging. I actually looked inside of my Jet saw before making this comment. It's tight!

[Cliff Rohrabacher]

1.)Can any table saw be outfitted with one? That depends on whether there is something to bolt it to. It's gotta be fixed so it moves with the blade.


2.)Do they have pawls attached to them or do you need pawls? Sopme do some don't. If the knife is doing it's job the pawls are overkill


3.)Can you no longer use thin kerf blades with them, didn't know if they came in different thicknesses. A knife appropriate for a thicker blade won't de any thing at all when using a thin kerf blade. You would need a different knife.

[Steve Sawyer]

Several folks here have pretty much answered your questions as asked, Aaron, but I started asking these questions a couple of weeks ago and have been doing some research on this, and thought I'd share what I've learned.

The safety function of a riving knife is the same as a splitter - it prevents the kerf from closing behind the blade on a rip, or allowing the stock that may bind between the blade and fence from getting caught by the teeth on the back of the blade which will lift the stock from the table and throw it back in the direction of the operator.

A riving knife differs from a simple splitter in some important ways:
It doesn't need to be removed from the saw when cross-cutting or doing a blind (non-through) cut as it doesn't extend above the top of the saw blade. Something we don't need to futz with gets used more consistently
It sits closer to the back edge of the blade, making it much more effective - less space for the stock to shift into the path of the blade
It provides some additional protection for the operator - blocking contact to the back edge of the blade - in those situations where the stock is being pulled from the outfeed side of the saw
It's independent of (and won't interfere with) other blade guards and dust collectorsThe way it achieves all of this (as has been mentioned) is that it moves with the saw blade as it's raised, lowered and tilted. To work properly, the knife should be just slightly less than the width of the blade, which I would imagine creates some issues for folks with multiple blade widths, though as someone mentioned, on the big beefy machines that are coming equipped w/riving knives, there is less incentive to go with thin-kerf blades.

Now, If you're lucky (:confused: ) enough to have an old Craftsman contractor's saw, or a new Ridgid (that I swear either copied or bought the old Craftsman trunnion and blade-guard setup), you CAN have half of this covered. Those saws have a blade guard mount that tilts with the saw, and it would be pretty easy to cobble up a metal blade to replace the flimsy, pawl-equipped splitter on which the blade guard mounts, to serve the function of a riving knife. While it will tilt with the blade, it won't raise and lower. It does, however, have a very nice quick-mount feature that makes it easy to remove and re-install the entire assembly without running into blade alignment problems.

What I plan on doing with mine is to fabricate the knives (yes, I plan on making several) with a slotted mounting so that I can slide it forward or back to clear the blade as I change the cutting depth. The assortment will include a couple of different thicknesses to accomodate the two blade thicknesses (standard and thin-kerf) that I use. I might also make two different mountings to adjust the height of the knife from the table to accomodate both thicker stock and to accomodate the additional clearance needed when tilting the arbor.

So, while I'm waiting for that inheritance that will let me buy that SawStop, I'll still be able to enjoy the safety features of a jackleg "riving knife", albeit without all of the convenience of the real McCoy.

[Steven Wilson]

It sits closer to the back edge of the blade, making it much more effective - less space for the stock to shift into the path of the blade

That is the big safety feature of a riving knife. Whatever you make, make sure that your riving knife follows the curvature of your blade and sits right behind the blade