How did this kickback happen?

[robinson46176]

I would try that nickel test on some of mine but I spent all of my nickels on Shopsmith stuff...
I have a penny left but it will not stand up with the thing turned off.

[JPG]

JPG40504
I think you have definition and usual cause mixed here.Was just trying to show that the 'typical' understanding of kickback as it pertains to a table saw includes the 'pinch' effect which is the cause.
The definition of Kickback from Webster is 1 : a sharp violent reaction

I think what you are saying is the kickback you are most familar with is when a piece of wood is wedged or caught between the rotating blade and something else.

I have heard war stories from different wood workers telling of kickback incidents where a sharp violent reaction occurred and there was nothing wedged. This describes heath's incident and IMHO is not kickback in the 'usual' sense, although the untethered cutoff was indeed caused to kick back towards the operator. Semantics!!!

I guess I could say I saw an example of kick back when a piece of wood that was being cut literally exploded. Evidently there were tensions within the wood that when one of them got cut it make the wood reaction as if there was a bomb in it.

On a tablesaw kickback can occur any time the blade tries to push or throw the wood instead cutting through it. Using that definition, they are both 'kickbacks'.

However I think the pinched kickback is the more common occurrence and more common understanding. For those reasons, Heath was having trouble understanding how his incident happened with NO pinching taking place.

Flying pieces of wood are not good regardless of how we refer to its cause!:eek:

[heathicus]

However I think the pinched kickback is the more common occurrence and more common understanding. For those reasons, Heath was having trouble understanding how his incident happened with NO pinching taking place.

That is correct! Although I now have a few hypotheses regarding this specific incident and a better understanding of the matter in general.

Flying pieces of wood are not good regardless of how we refer to its cause!:eek:

Agreed!!

[allmond2002]

I realize this thread is fairly old and this is my first post ever, but there is something still that no one has touched on. Albeit maintaining control of both pieces is the best option. There is a possibility that feed rate may be the culprit in this instance. Thick material can increase the amount of heat being generated and may be causing the blade to dis-temper and warp. Thus causing the warped blade to cause the kickback. I only state this because when I was new to woodworking, I experienced a kickback similar to this while cross-cutting 4" rock maple. When the blade cools, I've seen it snap back to straight. There normally would be discoloration on the blade from losing it's temper if this is the cause.

[JPG]

I realize this thread is fairly old and this is my first post ever, but there is something still that no one has touched on. Albeit maintaining control of both pieces is the best option. There is a possibility that feed rate may be the culprit in this instance. Thick material can increase the amount of heat being generated and may be causing the blade to dis-temper and warp. Thus causing the warped blade to cause the kickback. I only state this because when I was new to woodworking, I experienced a kickback similar to this while cross-cutting 4" rock maple. When the blade cools, I've seen it snap back to straight. There normally would be discoloration on the blade from losing it's temper if this is the cause.

Excellent point! It does not need to get hot enough to 'lose' temper(and discolor), just hot enough on the periphery so that the expansion(about the circumference) causes the blade to assume a wavy shape(further increasing the heat) and prone to jam in the kerf. A stalled motor will occur if severe enough.

Do not sweat resurrecting a thread. It exposes new members to the subject matter and refreshes the older ones.

New input is always welcome!!!!(as are new 'posters':))

Welcome aboard!!!

[allmond2002]

Thank you for the welcome, hopefully I will be able to provide decent enough 2 cents on things I have knowledge of. And sometimes a quarter.

[jimsjinx]

I have always used a miter guage or a sled to do crosscutting. I have been taught that you NEVER use the fence to crosscut a piece that is not as wide as the blade, or at least close. The piece against the fence can get "cocked" in between the fence and the blade, thus kicking back. If I am reading this right. A home made sled is really the ticket with small parts. jimsjinx

[JPG]

After going back and re-reading Heath's original post, I believe this may be what happened.

The shoe was probably pushing the workpiece close to the fence. This would tend to cause the workpiece to rotate slightly counter-clockwise(rear end away from the fence and towards the blade). By standing to the right of the blade, you were probably pushing the shoe with your left hand. This would have a tendency to push the workpiece away from the fence... The shortness of the workpiece allowed the rear end to ride the smooth portion of the side of the blade until arriving at the teeth. . . .

I gotta ask, Why were you not using the miter gauge? Not to be a SA, but it is called a rip fence. That being said, there are times when it is necessary to 'do it that way'. I assume that was the first piece, not the only piece being cut.

FWIW I would never position myself as you described(right of the blade/fence?). Neither would I have used a shoe in that instance. 4" is a safe distance from the blade so I would have gripped the workpiece between thumb and forefinger(and others) with the thumb(right hand) pushing feeding and towards the fence and the fingers pushing the workpiece against the fence. I would place belly button to the left of the table edge(Mark 5 small table!). This allows more easily maintaining the workpiece pressure against the fence. If I should get careless, the space between my arm(under the 'pit') and my larger trunk is wide enough for that piece to fly through.(that is unproven, as I have never 'had the problem' . . . . yet). I would also have my left hand ready to pull the 'cutoff' away from the blade.

JMHO Not necessarily a recommendation for everyone!

[jimsjinx]

JPG said it better than I could. That's what I was thinking. When the part went clockwise between the blade and the fence, it hit the teeth and BAM! Nice decription! jimsjinx

[heathicus]

It's been a while since this happened so I'll try to answer these questions as well as my memory will let me!

After going back and re-reading Heath's original post, I believe this may be what happened.

The shoe was probably pushing the workpiece close to the fence. This would tend to cause the workpiece to rotate slightly counter-clockwise(rear end away from the fence and towards the blade). By standing to the right of the blade, you were probably pushing the shoe with your left hand. This would have a tendency to push the workpiece away from the fence... The shortness of the workpiece allowed the rear end to ride the smooth portion of the side of the blade until arriving at the teeth. . . .

I gotta ask, Why were you not using the miter gauge? Not to be a SA, but it is called a rip fence. That being said, there are times when it is necessary to 'do it that way'. I assume that was the first piece, not the only piece being cut.

FWIW I would never position myself as you described(right of the blade/fence?). Neither would I have used a shoe in that instance. 4" is a safe distance from the blade so I would have gripped the workpiece between thumb and forefinger(and others) with the thumb(right hand) pushing feeding and towards the fence and the fingers pushing the workpiece against the fence. I would place belly button to the left of the table edge(Mark 5 small table!). This allows more easily maintaining the workpiece pressure against the fence. If I should get careless, the space between my arm(under the 'pit') and my larger trunk is wide enough for that piece to fly through.(that is unproven, as I have never 'had the problem' . . . . yet). I would also have my left hand ready to pull the 'cutoff' away from the blade.

JMHO Not necessarily a recommendation for everyone!

I wasn't using my Shopsmith, but a larger Craftsman table saw. Everything, except the cut off piece, was to the right of the blade. Fence, shoe, workpiece, and me. Why didn't I use the miter gauge? Because on either side of the blade, the miter slot is far enough away that, with a 4" wide piece, only about 1" of it would be in contact with the miter gauge making it very difficult to control. I did not use my miter gauge fence/extension thingy at the time because it was tore up and I didn't feel that I had much additional control over the piece than if I weren't using it at all. I should have made a new one, but didn't.

So the fence was to the right of the blade. Workpiece between the blade and the fence. Shoe holding down that workpiece. Me standing to the right of the blade, controlling the workpiece with the shoe. I don't recall which hand I was using, but I didn't have any trouble with this piece of wood.

To the left of the blade was nothing but the cut off piece. There was nothing to wedge it against the blade. It was completely free and alone on the left side of the blade. This was the piece that suddenly disappeared in a violent kickback.

What I now think happened is that I had the blade raised too high. Although the cut off piece was not "wedged" against the blade, it did still twist slightly (away from the back of the blade, or toward the front of the blade). Although it was behind the teeth, the corner of the cut off was caught by one of the deep gullets on the blade. Instead of riding against the smooth of the blade, that gullet caught the workpiece and threw it.

Now, if I were to do it again, I would stop and take the time to repair/replace the miter extension so that both workpiece and cut off were pushed all the way past the blade. Would that be the correct thing to do? (When I get my shop rebuilt, one of the first things I hope to do is build a cutoff sled.) Reaching over the blade with my left hand to control and pull the cut off away from the blade still scares me. Actually, having any part of my body cross the path of the blade makes me nervous. Is that really safe?

My reason for starting this thread is that I had always heard that as long as there is no way for a cut off piece to wedge itself between the blade and a fence (or other object), then it wont kick back. But it did. My experience with that kickback was contrary to everything I had read and heard.