Kickback with Riving Knife?

[Marty Tippin]

I don't know whether I'm just lucky or if the riving knife on my table saw (Grizzly G0715P) is saving me from my own stupidity, but I've never had anything even remotely close to a kickback incident and I've done some boneheaded things.

There was a recent discussion in another thread regarding using the table saw fence in conjunction with a cross-cut sled and I readily admitted to using that combination somewhat frequently without incident, with the proviso that I always make sure to hold the stock that would otherwise be "trapped" between blade and fence firmly in place against the rear rail of the crosscut sled. Several folks with a lot more experience than me pointed out that its just a matter of time before I take a board in the face. But is it really?

I don't assume that a riving knife completely eliminates the possibility of kickback but I wonder: On a table saw with a riving knife properly installed, what kind of Stupid Moves (tm) can still result in a kickback?

[Erik Loza]

I've witnessed it "nearly" happen at a trade shows on more than one occasion. With the rip fence (this being a sliding table saw) toed too far into the off-cut piece's travel.

This might surprise you but in my experience, it's most commonly commercial shops and even dealer reps (no joke...) who have no clue about how the safety features are supposed to work. Hobbyists like are the ones to take time to think about it.

Erik

[Ben Rivel]

IMO its pretty hard to have a kick back when a proper riving knife is installed. Thats why they have become mandatory in so many places. I honestly cant think of any situation (minus those that involve the use of the miter gauge and the fence at the same time, which is a no no anyway) that would cause one when using a riving knife but people say it can still happen. Best guess would be if the stock was very thin and it lifted up maybe past the height of the riving knife and twisted...?

[Erik Loza]

The one I most often see is where the offcut piece gets pinched between sawblade and the rip fence, on the way out of the cut. It is not so much improper adjustment of the riving knife (not sure if you have space or shim these on cabinet saws. On our sliders, they basically drop right in and are automatically indexed) as improper adjustment of the fences.

The last time I witnessed this was at IWF. We had a big slider in the booth which was powered, but not intended to cut with. No dust collection or material on hand. We just wanted to be able to show it running for customers and because of this, we don't really calibrate the fences or that sort of thing. My colleague and I were in the booth and I heard the machine start up, then cutting right behind us. I turned around and some rep from a regional SCM Group dealer had taken it upon himself to do a live demo with a sheet of melamine. The rip fence was too far forward and just I look over, you can see the offcut piece "dancing" between the blade and the rip fence, which is TERRIFYING. We shut the machine down before anything happened but the worst-case scenario is that the piece jumps off the table and goes flying some random direction.

Erik

[Frank Pratt]

Until a few months ago I'd never used a saw with a riving knife. I've always been very careful but still encountered several cases of very minor kick back over the years. Now, using a riving knife is so much less stressful. It's very unlikely you could get kick back with a riving knife & a guard.

[Jim German]

You certainly could still get a kickback with a riving knife. Easily possible doing a crosscut (as others have mentioned)as the riving knife frequently wouldn't even be doing anything there. But you could still have one with a rip too. If you get board with some funky grain or a knot it could easily still bind up on the blade and kickback even with a riving knife. A riving knife is a great feature and will prevent most kickbacks, but you still need to use proper technique and not stand directly behind the blade because it can still happen.

[Bob Vavricka]

If your sled fence extends to the right side of the blade and you are keeping it tight against the fence of the saw and sled, then I think the chance of a kickback is low. The problem becomes when the piece is trapped and the leading edge of the cut off piece is pulled away from the fence, it pinches and then causes the kickback. The way you are doing it wouldn't be any different than using a stop block on the fence of the sled to cut pieces to the same length. It could be a problem if the cutoff piece is long and the fence is supporting the cutoff along its full length. Then it could be difficult to keep it from binding and causing a kickback. Just my opinion.

[Peter Quinn]

Say you have a 10" blade, it's up a bit over 1 1/2" to get past the sled and wood being cut, so front to back of blade projection is maybe 8"? Cross cut 5" parts....riving knife is not helping you, create a little twist, or the odd random crumb gets between fence and stock....can get ugly, I've seen it happen, it's not theoretical. I cross cut narrow stuff all the time on a sled with a captive stop, in that case I'm no where near the back of the blade, the front of the blade is always pushing back and down, so there is no real danger. It's when you pass the half way point of the blade, and particularly the rear teeth, that the "board chucker" is set up.

[Keith Weber]

I honestly cant think of any situation that would cause one when using a riving knife but people say it can still happen.

Well, consider this one... you have a board 4 feet long and 4 inches in width. Now you want to crosscut it into two, 2-foot long pieces using the stock miter gauge that came with the saw. Perfectly normal cut unless you decide to set your rip fence at 24" and use it in conjunction with the miter gauge (end of board riding along the rip fence. After the cut, you still have push a 2-foot wide by 4" deep board past the blade while it's snug between the blade and the rip fence. Most people here (hopefully) would see this as a very dangerous operation.

The thing is (with a narrow board like that) is that the riving knife isn't going to help you out. The riving knife is behind the blade. If that board twists at all when it cuts through, it has every opportunity to put side pressure on the the back of the blade before it even gets to the riving knife. If it doesn't kick right away, it will once it contacts the rising, rear teeth (which, again, happen ahead of the riving knife.)

Riving knives are great and can certainly decrease the number of kickbacks, but it doesn't prevent them all. It's fun to say that you've never had a kickback... until the day that you have one. Your greatest defense against kickbacks is using your brain (don't do dumb things, and don't become complacent.)

[Ben Rivel]

Well, consider this one... you have a board 4 feet long and 4 inches in width. Now you want to crosscut it into two, 2-foot long pieces using the stock miter gauge that came with the saw. Perfectly normal cut unless you decide to set your rip fence at 24" and use it in conjunction with the miter gauge (end of board riding along the rip fence. After the cut, you still have push a 2-foot wide by 4" deep board past the blade while it's snug between the blade and the rip fence. Most people here (hopefully) would see this as a very dangerous operation.

The thing is (with a narrow board like that) is that the riving knife isn't going to help you out. The riving knife is behind the blade. If that board twists at all when it cuts through, it has every opportunity to put side pressure on the the back of the blade before it even gets to the riving knife. If it doesn't kick right away, it will once it contacts the rising, rear teeth (which, again, happen ahead of the riving knife.)

Riving knives are great and can certainly decrease the number of kickbacks, but it doesn't prevent them all. It's fun to say that you've never had a kickback... until the day that you have one. Your greatest defense against kickbacks is using your brain (don't do dumb things, and don't become complacent.)
Sorry, should have worded my statement "any situation where the fence being used with the miter gauge wasnt involved". I forget not everyone knows not to do that.

[glenn bradley]

Kickbacks come in different flavors. Certainly a properly positioned riving knife will make accidental contact with the rear of the blade almost impossible. Running improperly prepared or (and I shudder at the thought) un-true lumber across a tablesaw is dangerous in many operations; please use your bandsaw for this stuff. A tablesaw is a simple machine; it uses straight and true reference surfaces from a piece of material to control the path of that material in a straight line through a spinning blade that is positioned relative to those straight and true reference surfaces. Now, if your reference surface is a 2x4, you will have issues; rough cuts at best, burning or kickback at worst. You can't move something irregular along a true path past the blade. The irregular surfaces of the material riding the regular surfaces of table, fence or gauge will deviate the feed path and . . . well, you know. Joint, plane then rip and crosscut. JMHO ;-)

[Frank Pratt]

OK, I wasn't thinking very hard when I did that last post. But there were some pretty unsafe practices proposed there that common sense would rule out.

[David Kumm]

It should also be noted that the riving knife or splitter must be sized correctly. Thickness should be between the plate and tooth width. A riving knife thinner than the blade plate may or may not work. Dave

[Prashun Patel]

A riving knife can only do its job if the piece is long enough to reach it. For cross cuts, there may be some time between when the offcut is freed from its main piece (which is properly held by the miter/sled fence, and when it reaches the riving knife.

I do think that clamping the good side and offcut pieces to the sled fence will work to prevent kickback. In short, i would only 'risk' this if the off cut was sufficiently wide to allow proper registration and clamping against the crosscut fence.

I mean, I often use a stop block with my sled and miter gauge. That essentially traps the cut too, but the miter fence extends the full length of the piece and pushes the piece through true and straight.

[Andrew Hughes]

I have not had a problem with kick back on my shops table saw.But the little job sites saw I've used in the past are the ones to watch out for.With no jointer around a underpowered motor that stalls in a cut.Will transfer the energy into the wood and shove into your belt line.I got some scars to prove it.

[Art Mann]

My opinion is that if someone is trapping the work piece between the saw blade and fence, a strong kickback is possible whether there is a riving knife present or not. If the wood gets skewed, that blade is going to toss that piece whether the riving knife is there or not. The wood doesn't even have to go forward enough to make contact with the riving knife. A riving knife primarily protects against kickbacks during a rip cut.

[Jim Becker]

With a riving knife, the most likely way for a kickback to occur is if the workpiece lifts up off the table for some reason, and that's potentially because of material that's not flat or the blade isn't high enough for the cut.

[Prashun Patel]

In fact if the wood makes contact with the roving knife it most likely will not kick.

[Eric Schmid]

I have spent many more years on a saw without a riving knife or even a splitter than with one. I can tell you some pretty ugly stuff can happen on those machines and you don't have to do anything stupid. The margin of error is pretty slim.

A knife is so much safer, but it should not change the way you operate the machine from the standpoint of safety. I handle my saw with the riving knife the same as I do the others.

I don't know how you use your sled, but I am typically right in line with the blade due to the ergonomics of the sled. If something goes wrong I'm likely in the path of the projectile. I've been that guy and once you've had a 2'x2' plywood Frisbee sailing past you and through the back window of your shop, you realize this is not an experience you'd like to have again.

I can tell you that freehand cutting with a riving knife (or without) will result in kickback.

[Marty Schlosser]

I'm going to chime in here now, as most of the posts have been in relation to crosscutting operations. I'd like to talk about ripping operations, as from my experience, they're the most dangerous of the two.

To limit the possibility of kickback, I follow the usual safety practices, which have already been mentioned in this thread (i.e. joint one face first, joint one edge, then do the rip). My saw's fence can be moved front and back, so I set it so the end of it is a few inches - at most - beyond the far edge of the sawblade. That way, if the board warps due to stresses being relieved as the rip is happening (and believe me, this happens more than one would believe, even with dry lumber), there will be no place for binding to occur. A word of advice, though; you'll have to change your ripping technique to keep the board moving directly along the same plane as the face of the fence, as when it gets to the end of the fence there's no longer a fence there to keep it going straight.

[Charlie Fox]

reading this thread reminds me why i always wear a face shield when using my table saw... ;-)

[Ben Rivel]

reading this thread reminds me why i always wear a face shield when using my table saw... ;-)
Is it common for kick back incidents to injure people in their face?

[Charlie Fox]

i would think any part of your body above the table is in range! i have had small pieces fall down the throat when at 45deg and shoot out and hit my arm in the delt - thats too close! ricochets can happen also! i just feel much better knowing my face, head, and eyes are well defended

[Roy Turbett]

With a riving knife, the most likely way for a kickback to occur is if the workpiece lifts up off the table for some reason, and that's potentially because of material that's not flat or the blade isn't high enough for the cut.

+1 Where I've seen this problem during a rip is when the piece isn't supported on the infeed side and lifts off the table. This sometimes happens when the operator pushes down on the back of stock before it reaches the table. Raising the blade helps but the best solution is to use flat stock and keep it tight to the table and the fence.

[Jim Becker]

I'm going to chime in here now, as most of the posts have been in relation to crosscutting operations. I'd like to talk about ripping operations, as from my experience, they're the most dangerous of the two.e board moving directly along the same plane as the face of the fence, as when it gets to the end of the fence there's no longer a fence there to keep it going straight.
Actually, I was really only thinking of ripping when I mentioned "board lift" as a concern...

[Jim Becker]

+1 Where I've seen this problem during a rip is when the piece isn't supported on the infeed side and lifts off the table. This sometimes happens when the operator pushes down on the back of stock before it reaches the table. Raising the blade helps but the best solution is to use flat stock and keep it tight to the table and the fence.

I actually have to be very careful about this when I'm doing a "traditional rip cut" with the fence on my slider since the combination of body position and shorter "table" in that area makes it harder. I agree with your advice, too.