Help me understand this kickback scenario

[James Adinaro]

Hi all - had an "incident" (no injuries) in the shop a couple days ago. I think I understand what happened, but want to get any other opinions before I consider it closed.

The equipment: Jet left tilt Xacta saw. I've added the Biesemeyer drop-in splitter, which was in place for this cut. I did not have the pawls on the splitter though. (I've actually cut the splitter down so that it will fit through my crosscut sled. I found that I kept removing it to use the sled and then would forget to put it back. Since the splitter fits in my sled now, I'm much better about leaving it on.)

The cut: I needed to rip a 1" piece from the short end of a 3/4" (24" x 48") slab of the green, woodcraft phenolic plywood. Though I have a 52" fence, there is a support pole in my shop which effectively limits my rip capacity to 30" - so ripping the piece on the offcut side wouldn't work because I couldn't get the 48" on the table. For some reason, it didn't occur to me to use my wall-mount panel saw. So I set the fence to 1" and went at it. Due to the weight and length of the plywood, it wouldn't balance on the table to the left of the blade, so I had to stand to the left of the blade and guide the slab across that way, leaving the "workpiece" unguided.

Thump: As I finished the cut, I heard a loud "thump". I immediately shut down the saw and verified that I still had all body parts working properly. It took me a minute to realize what had happened - the 1" piece was impaled 3 inches deep in the drywall 8 feet away and poking out.

What I think happened: As I finished the cut and the 1" piece became free, I think I bumped the end of it with the large "offcut" I was guiding. This caused it to pivot against the back end of the fence and into some part of the blade, where it proceeded to blast off across the shop.

At first, I thought that the missile might have gotten into the gap between the back of the blade and the splitter. I was thinking a riving knife might have helped avoid this. But now I don't think that happened - since I wasn't touching the 1" workpiece, it would have stopped moving as soon as it was cut free by the front of the blade. I think the pawls might have helped, but a riving knife by itself, not so much.

So my questions are:

1) Am I understanding this right? If not, what did I miss?
2) Would a riving knife setup have helped?
3) Besides the panel saw (though a 1" piece on the safety speed cut still would fall through the rails and get dinged up), did I overlook another obvious way to make the cut?

4) Could I possibly use this to rationalize the purchase of a new Unisaw when it becomes available? :-)

Thanks all,

James

[Cary Falk]

James,
Once the 1" piece was free from the main board it was free to rattle around between then fence and the blade. The spinning blade made contact with the board and accelerated it across the room. My splitter pushes the board against the fence. I don't know how much pressure yours presses the board against the fence.I'n not sure any amount of pressure that would have allowed you to still move the board through would have helped.The paws would have definitely prevented the board from shooting out from the table saw. A riving knife would have not helped much because the only difference between you setup and a riving knife is your splitter is at a fixed height. I probably would have cut off the piece with a guide and a circular saw. I have had a 1/4x1/4" piece of wood that I was removing from the edges of a recessed cabinet door shoot across the room and lodge itself into the garage door before.

[Frank Drew]

James,

IMO the 1" piece was almost guaranteed to kick back; there was nothing preventing it from doing so and even the wind from the spinning blade could have been enough to jostle the unrestrained piece into the blade (with the fence on the right it had nowhere else to go), thus the resulting missile launch. The cut as you describe (if I've understood you correctly) wasn't the way to do it; you needed to find a way to support the larger piece of ply while still guiding and pushing the 1" piece through the cut until it cleared the back of the blade.

[Lee DeRaud]

C'mon, admit it: what you really want is an excuse to buy a Euro-style slider.

[Andy Casiello]

James,

you needed to find a way to support the larger piece of ply while still guiding and pushing the 1" piece through the cut until it cleared the back of the blade.

+1. Stock on both sides of the blade on a TS need to be controlled until they are past the blade. I did something similar to what you are describing once. :eek: It quickly convinces a guy to put all safety measures into full effect during every cut. :o

[glenn bradley]

+2 Uncontrolled stock.

[Chip Lindley]

The cut you attempted to make is what sliders (or sliding tables) do best. Without the kickback pawls in place you were doomed to failure, as the offcut was free to bind between blade and fence and kick back! The same will happen almost every time this cut is attempted. To Do this cut, you must support the sheet in some fashion, while you concentrate on the 1" strip being cut against the fence. The whole sheet is one gigantic offcut! If the sheet is supported it will separate from the strip as you use a push stick to complete the cut. This is *bass-ackward* Awkward at best!!

Better yet, either drag the saw away from that post, so the full width of your fence can be used, OR get an Exaktor sliding table to attach to the left side. My EX60 makes short work of cutting narrow strips off a large panel. It is big bucks but with the addition of a Modulus scoring attachment, is the next best thing to a *real* slider.

[Nissim Avrahami]

This is a kind of a kickback that I call "Operator Induced Kickback"....

The piece between the blade and the fence would never get out unless you use a push stick to push it out of the blade...and that's the ABC of a kickback....the workpiece binds between the fence and the blade, pushed into the back up-raising teeth and WOOOOM....

The piece between the blade and the fence should be ALWAYS pushed with a push stick/block/shoe till it leaves the blade area...

You can read it in every book - "Never use the rip fence as a stop for cross-cutting with the miter gauge"...what you did was exactly that, just without the miter gauge...

Even a riving knife would not help in this case...in spite of the "legend" that riving knife prevents kickback -- no -- the riving knife just minimizes the chances of kickback (in Europe all the table saws have riving knife and still we are getting kickbacks).

I'm very happy that you are safe and sound and, I'm sure that you've learnt your lesson and will never try such a method again.

Regards
niki

[David DeCristoforo]

What everyone else said. Those pieces can shoot out with enough force to penetrate the skin through heavy denim. The ultimate example of this is to tilt the blade into the fence to cut a small triangle off the end of a piece of stock. Of course this should never be attempted but I watched someone do it once and there was someone even dumber who walked behind the operator at just the moment when the falloff piece was ejected. It actually stuck in his thigh like an arrow and the only sound louder than the "splang" sound the saw made was the shriek from the guy when he got impaled by a blunt triangle of plywood.

[James Adinaro]

<<"Never use the rip fence as a stop for cross-cutting with the miter gauge"...what you did was exactly that, just without the miter gauge...>>

Ahhhh! Thanks! That really hits home. I'm always good at following that rule, but it never occured to me that that is exactly what I was doing in this case.

Thanks to all for the fast replies. The sliding table certainly would have helped out in this instance. Something new for the wish list....

Thankfully, this lesson only cost me a drywall patch job...

J

[Karl Brogger]

This is a kind of a kickback that I call "Operator Induced Kickback"....

LOL, there is another kind?

[Nissim Avrahami]

LOL, there is another kind?

The other kind is "Reactive wood" kickback, when the wood is severed by the front teeth and springs toward the fence but, the fence is "stronger" so the only way that the wood can go is into the awaiting back teeth and from here, it takes a split of second till it becomes a UFO...it's not an operator error, it's the nature of some woods and you don't know it till you "get" it... :)

Regards
niki

[Steve Rozmiarek]

C'mon, admit it: what you really want is an excuse to buy a Euro-style slider.

+1 on the euro-slider...

[John Thompson]

Again...what eveyone else said but... the biggest mistake you made was the fact you mentioned you have a wall mount panel saw..

"it didn't occur to me to use my wall-mount panel saw"... James

Why and I will add it should have as it is as safe if not safer than the slider when cutting sheets.

Glad you weren't hurt....

Sarge..

[Alan Tolchinsky]

+1. Stock on both sides of the blade on a TS need to be controlled until they are past the blade. I did something similar to what you are describing once. :eek: It quickly convinces a guy to put all safety measures into full effect during every cut. :o

Yes, I agree. Any piece between the blade and fence has to be under control all the way through the cut. I do this with a push shoe and/or magnetic hold downs. So basically no pieces should go through that fence/blade area without constant control by the operator. I'm glad you were not injured and I think you are very wise to make this a learning experience for you and all of us. Instead of just glossing over this you asked why it happened.

[Karl Brogger]

The other kind is "Reactive wood" kickback, when the wood is severed by the front teeth and springs toward the fence but, the fence is "stronger" so the only way that the wood can go is into the awaiting back teeth and from here, it takes a split of second till it becomes a UFO...it's not an operator error, it's the nature of some woods and you don't know it till you "get" it... :)

Regards
niki


To me that just means that person isn't hanging on properly, and still operator error.

I've probably had 20 kickbacks in the past ten years. Not one was anythings fault other than my own.

[Chip Lindley]

Of course I am glad you were not hurt, also!! Goes without saying. I was *really injured* once, when such a kickback hurled a slim piece of oak backward out of my tablesaw and stuck right through.......TBC hehe!

[Chip Lindley]

Um....Errr...Ahhh....Well.....

the missile shot through, NOT my own flesh, but an expensive roll of new Formica laminate which just happened to be in line with the kickback! *Sad but True!*

[Nissim Avrahami]

To me that just means that person isn't hanging on properly, and still operator error.

I've probably had 20 kickbacks in the past ten years. Not one was anythings fault other than my own.
Hi Karl

Well we just have different way of operation...you prefer to "hang on" on the workpice and I prefer to use a short fence and keep my hands far away from the "war zone"...

I called it "Operator error" because as I know, only a few Americans are using short fence (one of them is our John Thompson - Sarge) and the majority are using the long fence that can lead to a kickback when ripping "reaction wood" (but you never know that it's "reactive" till you "get" it).

"Hanging on" on the workpiece is considered by me very dangerous because IMO it can lead to much sever accident in case the hand slips...especially - as I read an article by Kelly Mehler - that 95% of the American woodworkers do not use the blade guard...

On the pictures below, you can see my set-up for ripping solid wood...I can stand almost in any place and keep my hands far from the guarded blade...

Regards
niki

http://i208.photobucket.com/albums/bb151/matsukawa/TS%20Short%20fence%20rip/0001.jpg


http://i208.photobucket.com/albums/bb151/matsukawa/TS%20Short%20fence%20rip/0006.jpg


http://i208.photobucket.com/albums/bb151/matsukawa/TS%20Short%20fence%20rip/0009.jpg

[Peter Quinn]

The ultimate example of this is to tilt the blade into the fence to cut a small triangle off the end of a piece of stock. Of course this should never be attempted ...

Yea, We ran into a setup with some stair treads, 3 1/2" thick QSWO, 14 X 48, with a 110 degree back bevel on the leading edge. We had a set of 4" shaper knives made that would radius the leading and bottom edge as well as make the back bevel, but some material had to be removed to ease the shaping and the only saw we had to handle it was a right tilt 14" SCMI TS with a power feed. We were able to get three treads through on each pass back to back before the outfeed table became full, and then.....

So we set up a couple of solid core doors as a kind of back stop (like in baseball), painted a big target on them and warned every guy in the shop to stay away for the next half hour. WOW, what a show. Its not in retrospect the smartest thing ever done in a wood shop, but neither man nor machine was injured and all got a heck of a lesson on the fury of kick back.

Batter up!:eek:

James, I'm going to go out on a limb here and say that what you did was dumb, real dumb. Glad you were not hurt, don't do it again or you may not be so lucky. Put a backer on the panel saw, use a skill saw, mobilize that TS and do it right (move away from the pole), something. Maybe a bigger panel sled?