SawStop's Riving Knife - No anti-kickback pawls??

[Glen Blanchard]

I took a good look at the SS today at Woodcraft. It appears as if the blade guard/splitter combination has anti-kickback pawls while the riving knife has no such pawls. Is this correct? I have an overhead blade guard, so will not be using the OEM guard. I also have the Beisemeyer snap-in splitter on my current saw, which does have anti-kickback pawls - so I am used to having those pawls.

Is it even possible for riving knives to have anti-kickback pawls? Now that I think about it, if these things move up and down with the blade, how can pawls be attached to them? If riving knives cannot have anti-kickback pawls as a result of their very design, does this not pose a possible safety hazard (the very thing they are supposed to enhance)?

[Rob Bodenschatz]

Not sure if the Sawstop works the same way but my PM2000 has a riving knife and the pawls. The blade guard and pawls are attached to the riving knife like so:

50892
50891

The pawls pivot with the riving knife as it goes up & down.

[Roy Wall]

the knife is positioned 1-2mm below the top edge of the blade, for non thru cuts when they occur......the pawls won't work on this type of cut - so they're just on the bigger splitter arangement.

That's why the Sawstop has both types of riving knives........the one like on the PM2000 and the one for non thru cuts...

[Glen Blanchard]

That's why the Sawstop has both types of riving knives........the one like on the PM2000 and the one for non thru cuts...

Why would a riving knife even be needed on a non-through cut, as there is no possibilty of the stock collapsing on the blade?

[Roy Wall]

Why would a riving knife even be needed on a non-through cut, as there is no possibilty of the stock collapsing on the blade?

My guess is to keep the wood from pinching right behind the cut, wether a cc or rip.......as wood can do this...

[Glen Blanchard]

So if one will be using a 3rd party overhead blade guard with the riving knife, since there will not be any anti-kickback pawls, should one be concerned? Or is "one" merely being anal? :eek:

[Jim Murphy]

The Saw Stop comes with two riving knives. One comes with the bladeguard and pawls, and the other is just the riving knife. I wouldn't call the riving knife with the blade guard and pawls a splitter, because a splitter does not rise and fall with the blade, like a riving knife. This makes a riving knife safer than a splitter, because it is always a few millimeters away from the blade, now matter how high or low you set the blade.

I did a bunch of cross cutting with my sled the last couple of days, and used the stand alone riving knife, because the one with the blade guard, of course, wouldn't work.

[Nissim Avrahami]

The EU safety regulations are more strict than the US one.

Operation of the TS without the blade guard is prohibited, that means, no non-through cuts and no dado blade (the arbor is short and dado blade cannot be installed).

A riving knife must be installed but there is no any demand for kickback pawls.
I assume that riving knife is safe enough to prevent kickback, anyway, I never got kickback with this TS.

niki

http://i50.photobucket.com/albums/f321/avrahami/Rivingknife.jpg

[John Miliunas]

Glen, as the others have stated, the SS has two riving knives, one with and one w/o pawls. Having said that and, mind you, this is but one man's opinion, I actually don't see a big advantage in the pawls to begin with. (Let the flaming begin!:eek: ) Here's my logic behind that statement: Kickback will happen when the board exiting the blade will get skewed or pinched back into the blade, get picked up by the blade in its upward motion, get caught in that motion and then get thrown back in the direction the blade is moving. A good splitter or, in this case and much better, the riving knife eliminates that from happening. Hence, I'm not too positive about the effectiveness of the pawls.

Now, there's also the possibility of especially thinner/lighter pieces of wood just being picked up by the blade in its upward motion at the back. That's where your overhead guard really comes into play. I also have one of those (Excalibur) and I always set it up so that it virtually lays on the wood and I tighten it down to stay there. On pieces where that may be too cumbersome, I've actually gone and made an auxiliary fence, which is attached to my regular fence and I have a "T" track on it, where I mount featherboards to hold the material down against the table. :) :cool:

[Cliff Rohrabacher]

If the knife is doing it's job, the pawls are overkill

[Mark Rios]

The EU safety regulations are more strict than the US one.

Operation of the TS without the blade guard is prohibited, that means, no non-through cuts and no dado blade (the arbor is short and dado blade cannot be installed).

A riving knife must be installed but there is no any demand for kickback pawls.
I assume that riving knife is safe enough to prevent kickback, anyway, I never got kickback with this TS.

niki

http://i50.photobucket.com/albums/f321/avrahami/Rivingknife.jpg


Two questions, if I may Niki?....

First, when you say that operation without a blade guard is prohibited, is that even in your own home/shop/garage with the door closed? I understand that one couldn't get around the short arbor thing but how do they enforce a blade guard regulation like that in your own home?

Second, since you're unable to do dados on your table saw, where do you do them then, on your router table? Or is there a secret, magical dadoing machine that only EU residents are allowed to own and operate? ;) :D

Thanks very much.

I was all ready to wish you a Happy Thanksgiving but then I remembered that Poland was probably has it's T-Day for an entirely different reason and at an entirerly different time, sooooooooooo..................have a nice weekend!:D

[Nissim Avrahami]

Hi Mark

Well, of course they cannot control individuals and the regulations are for businesses or for the woodworking schools, but the TS design must be accordingly.

If you use a riving knife like mine, you don’t have any reason to remove the guard with the dust port, kind of encouragement not to remove the guard.

Another regulation that I forgot to mention is “The blade must stop rotating within 10 seconds” (from switch off) and my blade does.

No, we don’t have secret dadoing machine (yet), I make them with hand held router and jig like in this post
http://www.sawmillcreek.org/showthread.php?t=36938

Happy Thanksgiving (we don’t have this holiday in Europe).

Regards
niki

[Larry Halberstadt]

I saw a demo done by Kelly Mehler at The Woodworking Shows. He is also author of The Tablesaw Book from Tauton Press. Kickback is caused when a board is allowed to rotate to the point that the board rides up onto the top of the blade, at which point the board can be push toward you with considerable velocity. If the board cannot rotate, kickback cannot occur. Any type of splitter or riving knife prevents a board from rotating and is really the only protection that is needed against kickback. Anti-kickback pawls are just an extra measure of protection. A riving knife is better than a standard splitter because is rides closer to the back of the blade and the distance is the same at all blade heights. Any saw equiped with a riving knife shouldn't even need pawls. I have a Jet cabinet saw and I removed the pawls from my factory guard system. They really are more of a hinderance than a help.

[Jim Becker]

As Larry did...I removed the pawls from my Biesemeyer snap-in splitter, both because I dislike the marking they sometimes do to softer stock and veneer sheet goods as well as the way they can interfere with very narrow cuts next to the fence. I don't really believe they add much "protection" outside of a situation where material rises up on the blade which shouldn't happen if blade height is set correctly and proper hold-downs/push blocks are used to move the stock through the cut. They would be imposible to use with a riving knive since no part of the riving knife rises above the top of the blade...no place to mount the pawls! (Obviously, they could be accomodated on the same machine when a blade guard is being utilized for through cuts and the blade is raised high enough over the material)

[JayStPeter]

Personally, I feel the pawls provide as much negative as positive on the safety front. Both narrow cuts and narrow offcuts wind up trapped. So, I have removed mine and will likely remove them from any saw I own in the future.

[Matt Calder]

All,

Since we're on the riving knife topic, I have a question about setting them. On my Laguna TSS I need to remove the knife when using a dadoe stack. After the last time I did this, when I put a normal blade back on the saw, I found the riving knife exerts a slight pinch to the fence. Put another way, the knife seems ever so slightly closer to the fence than the blade is. I don't think it was this way before, but it might have been (I've only owned the saw a few months now). Is this correct? Should the knife be completely eclipsed by the blade or does this slight offset serve some purpose? Thanks for any help.

Matt

[lou sansone]

All,

Since we're on the riving knife topic, I have a question about setting them. On my Laguna TSS I need to remove the knife when using a dadoe stack. After the last time I did this, when I put a normal blade back on the saw, I found the riving knife exerts a slight pinch to the fence. Put another way, the knife seems ever so slightly closer to the fence than the blade is. I don't think it was this way before, but it might have been (I've only owned the saw a few months now). Is this correct? Should the knife be completely eclipsed by the blade or does this slight offset serve some purpose? Thanks for any help.


Matt


riving knife should be centered behind the blade. was there a shim that might have fallen out when you removed the knife ?

lou

[Phil Pritchard]

If you utilise a riving knife with a short (i.e. Euro-style) rip fence then the kickback pawls are completely superfluous. Kickback occurs when the workpiece contacts the rising teeth at the rear of the blade, something which can be caused by the workpiece rotating (in my experience uncommon) or (more commonly) the release of stresses in the timber causing the material to bend inwards onto the rear of the blade (or outwards causing trapping between the blade and the fence plate - one reason I detest the Biesmeyer fence and consider it an inadequate and potentially unsafe design). Pawls are really a half-way house solution designed to overcome the inadequacy of splitters as a safety measure - a sort of Band Aid piece of engineering.

As to dado heads being illegal in the EU - not true. There are however sufficient safety steps required in order to use them that they are "awkward" to use in a commercial environment with the exception of use on an overhead crosscut or radial arm saw. The alternatives are to either use a spindle moulder (shaper) for your rebates (faster, cleaner cut, safer, etc), use a RAS with a grooving head or use the aforementioned router. The stacked saw dado head is another second rate, half-baked and fundamentally unsafe piece of engineering which is fortunately disappearing over here in the face of safer alternatives.

Oh, and why make everyone (trade and private individuals) dance to the same safety standards? I think it has something to do with safety, doesn't it?

Phil

[Joe Dusel (Vista, CA)]

I think that the anti-kickback pawls are a goofy solution to the poorly designed splitters that come with a lot of the American and Asian import table saws. The fixed splitter design was all about making things cheaply. Using a riving knife you don't need the pawls. The safety standards in Europe are much tougher and if the pawls were needed the Europeans would require them. I have been using European saws for the past 16 years and I have never had any sort of kickback even on really difficult wood. I think it's great that Sawstop, Powermatic and Grizzly have finally come up with designs with riving knives that track the blade.

Joe

[Glen Blanchard]

Using a riving knife you don't need the pawls.

Thanks folks. Feel better now.

[Nissim Avrahami]

Hi Phil

You are correct. After reading the EU safety regulations, the manufacturers are given the permission to make an arbor long enough to accommodate a 15.5mm (39/64”) dado blade and there is a request to make a longer arbor for 19mm (3/4”).

For some reason, not all the manufacturers are using this permission (cost?) and if you look at my table saw (Metabo group), you will see that I even don’t have normal “Throat” to install the dado blade.

As you mentioned there are some demands for using dado blade like an adjustable blade guard (they call it Hood) that is not installed on the riving knife.

Sorry for the misleading, I thought that if my TS is built like that (2005 German production), it’s because of the safety regulations.

Regards
niki

[Jules Dominguez]

Just a thought...something that's not likely to happen but could... say you're ripping a board, and the heel of your push stick breaks, or your hand slips or the push stick slips, and momentarily you don't have control of the board. Even without the workpiece getting cattiwampus with the blade, the friction between the blade and the wood could be enough for the blade to throw the board back at you. If this occurred after the workpiece is far enough into the cut for the pawls to be in contact, they would prevent that happening.
Try pushing a board into a rip, without pawls, and then release it part way through the cut... without pawls or a featherboard, what do you think would happen?

[Phil Pritchard]

Try pushing a board into a rip, without pawls, and then release it part way through the cut... without pawls or a featherboard, what do you think would happen?
I know what happens from experience. Providing you are running with a Euro-style rip fence (meaning there is no chance of "pinching") and the the workpiece isn't too heavy it will start to move backwards very slowly towards the operator. It will not normally be converted into a hurtling projectile at that stage unless the piece is very small or very light. If the blade is fitted with a (properly adjusted) crown guard that will also act to prevent the workpiece being llifted too far off the saw table and thrown - another good reason to use the guard. A proper riving knife is so narrow it cannot support pawls and with the right set-up they are superfluous

Phil

[David Weaver]

I know what happens from experience. Providing you are running with a Euro-style rip fence (meaning there is no chance of "pinching") and the the workpiece isn't too heavy it will start to move backwards very slowly towards the operator. It will not normally be converted into a hurtling projectile at that stage unless the piece is very small or very light. If the blade is fitted with a (properly adjusted) crown guard that will also act to prevent the workpiece being llifted too far off the saw table and thrown - another good reason to use the guard. A proper riving knife is so narrow it cannot support pawls and with the right set-up they are superfluous

Phil

That's exactly the same thing that happened to me last night - using a biesemeyer fence. The reason that it happened that way, though, is because I was using two grip tites to pull the board toward the fence, as well as a throat-plate mounted splitter. I wouldn't do this without those, but I was ripping 1 1/2 inch wide strips of 5/4 maple to make a butcher's block, and without outfeed help, it can be a pain to get to the pieces without having my fingers near the blade - so I push a piece part of the way through, and go pull the previously finished piece off the outfeed rollers, and then come back and do the same thing with the next - so there's always one piece finished, and another in the cut. Then, I can just use the next piece to push the prior piece through.

I didn't push one of the pieces in far enough to get to the rear grip tite, and the front had worked its way up, and the piece did exactly what you described. It wandered straight back about 6 inches, which made me ecstatic with a standard setup. Without the griptites and the MJ splitter (which someone on here recommended) - well, without that, I wouldn't walk away from a non-through cut.

It's a good compromise for those of us with biesemeyer fences.

[Seumas McCombie]

macduff uses two variations, one over-head and up front of the blade or cutting tool, and or on the fence, again placed in front of the blade. As the cut is completed the pawls do not have contact with the material ( even small pieces don't hang up ) as an added safety feature the pawls with other safety additions automatically drop behind the material at completion for the next height and width of cut, and are clear to push out with his innovative push stick. slainte mhath macduff aye ready