Time for another safety thread

[Ed62]

Safety can't be talked about too much when we like to play with the toys we play with.

We've all heard about kickbacks that caused the operator's hand to be pulled into the blade. But why isn't the hand pushed away from the blade if kickback happens? The stock is surely shot back in our direction. Use your blade guard and push sticks.

Here's my theory on why it happens, but I've been proven wrong before on my way of thinking, and I'm open to other views. When kickback happens, the back part of the blade raises the stock off the table. When the stock is quickly raised, the remainder of the stock (still in contact with the table) is pulled forward very quickly. Your hand is also pulled forward with a lot of force, and it's too late to stop it from contacting the blade area. I think understanding why bad things happen, makes a person less likely to get hurt.

Ed

[cabinetman]

Well, hi Ed...where have ya been? You OK?

I've never had my hand pulled into the blade when kickback occurs, and I've had plenty of them. I think the hand goes into the blade when you stick it in there (operator error). That happens when there is a loss of concentration, or doing something you shouldn't.

The back of the blade can induce kickback, and so can the front. A blade with slight elevation above the stock has a lifting effect on the stock as it enters the blade. During most kickbacks, it's so darn fast you really don't get a good look.

.

[Ed62]

Hi Mike,

I've been just fine, thanks. Just a lot going on in life.

I'm glad you mentioned the possibility of the front of the blade causing kickback, as I never considered that. It's not hard to understand how a lower blade could cause that, but it seems to me that probably more than 90% of kickbacks would happen from the back of the blade. Am I missing something? Just trying to get my head around that.

Most of us have probably encountered kickback at some point, and it's always scary even if we luck out and don't get hurt. I consider myself very lucky, with the worst for me being a very sore gut for a while. No blood flowing.

Ed

[jackellis]

I've gotten in the habit of using featherboards, push sticks and crosscut sleds. The blade guard and splitter rarely come off, and then only for the kinds of cuts that don't generate kickback but do cause a lot of anxiety.

[durango dude]

When I make legs for furniture - I split an inch (3/4 inch) off the 2x4 to turn it into a 3x3.

When I do this - I regularly run into kickback. Having the saw propel a 3/4" inch rocket at you is a wake up call ---
so I use push sticks.

The anti-kickback reduces this problem a lot - but mine isn't on the saw right now (I have a zero clearance plate on the saw, at the moment).

[pelligrini]

The anti-kickback reduces this problem a lot - but mine isn't on the saw right now (I have a zero clearance plate on the saw, at the moment).

You can cut a slot in your ZCTP to accomodate your riving knife. Using a ZCTP doesn't mean you have to go without a riving knife or guard.

[Richard in Smithville]

Hi Ed. Great to see you back on the boards!

[Stytooner]

I think there are really two types of kickback. Major and minor.
Not trying to diminish the danger from either. I have been speared in the side more than once from what I call a minor kickback.

A major kickback is where the stock is lifted at the rear of the blade and then travels over the crown of the blade toward the operator. It can and does often pull hands into contact with the blade. It is nearly instantaneous, so very little time between start to finish on a major kickback.
A minor kickback is when a part gets slung forward by the front teeth on the blade. Much less severe of a kickback, but still capable of shooting stuff forward at over 100 MPH. Anything hitting you that fast is dangerous.

I often see both types of kickbacks discussed as the same kind of occurrence.
I don't think this is really true. Each have different causes, though both can result in serious injury. A riving knife would likely stop a major kickback, but cannot impede a minor type. A blade guard can help with both types, but isn't 100% effective. If the guard is sitting on the offcut when it gets slung forward, it may slow it down some, but not totally prevent that action.

Being aware that the potential for kickback exists and use of safety aides really does reduce the risk of injury. No one thing is 100% effective against injury on a table saw. Risk of injury and potential danger is always there. Knowing this and preventing known causes with the use of safety aides is good practice. This applies to any tool.

[leehljp]

Going in a different direction from the general discussion on kickbacks, I don't think the blade or kickback pulls the hand into the blade as much as the forward pressure of the hand carries it into the blade.

When pushing/feeding takes a little force (by arms and hand), it is this forward motion force that takes the hand into the blade. When "some" kickbacks occur, there is a certain amount of force being applied by the hand. AS long as the hand is also being used to place a little downward force to keep the board from rising, then when the board is near the end of the cut, suddenly the side near the fence is raised, and the kickback occurs. This takes about 1/10 of a second. the other side of the board in which the hand was pushing suddenly leaps forward because the resistance of the blade suddenly is gone. The same "forward pressure against resistance" happens on kickbacks or no kickbacks. Kickbacks are just another factor in the equation but not the primary reason for the hand meeting the blade.

Again: The forward force of the hand meets resistance of the wood in the blade during the feed. As soon as the blade emerges on the backside of the rip, resistance is suddenly (instantly) gone and the forward pressure of the hand/arm pushes the hand into the blade. When this occurs with kickback, it is because the pressure is suddenly released from the wood/blade and the forward motion force of the hand carries it into the blade. Just my opinion.

When the hand nears the blade on the feed - This is where "awareness" of forward feed pressure is paramount.

[JimD]

I am not sure what causes kickback, I will accept your explanations, but I don't think we need to know to be safe. To me, the two key things are to keep your hands a safe distance from the blade - regardless of how - and to keep control over your workpiece - regardless of how you do it. If you don't do these two things you are at risk.

I had my ROS shoot a small leg for an end table - 1 3/4 square by 4 inches long solid oak - across the shop recently. I wasn't controlling it because I got tired of my hand touching the sand paper. So the tool threw the workpiece. Any table saw has a lot more power than a ROS. It cannot overpower you unless you let it. But it can heave the wood pretty good if you let things get out of control.

Jim

[Ed62]

I'm glad to hear the opinions of others on this. Thanks to all. Even though we'll probably never know what really happens, at least we talked about some of the possibilities, and maybe the thinking about safery will carry over into our next time in the shop.

In my mind, Hank has a point about the hand actually having a forward push on the stock, and I think that, coupled with the stock shooting forward, causes the hand to possibly meet with the blade on the rear of the blade kickbacks. So for now, that's what I'm going with.

Hi Ed. Great to see you back on the boards!

Thanks, Richard. Good to be here again.

Ed

[leehljp]

More on the force/pressure/thrust of the hand towards the saw blade:

Here are some examples of "human muscular reactions to force" (my term - there are probably other more correct muscular physiology terms.) Stand in a narrow doorway with arms and hands to the side. Then swing out the arms/hands until they touch the edges of the doorway. Press/push hard for 30 seconds. Stop and then move forward or backwards a step and relax the arms to the side. The arms will have a tendency to move outward. This is a normal reaction. The point here is that there are natural muscular neurological reactions that our body does that we do not realize or even think about.

In the same way, when getting a hair cut - the barber or stylist will move your head around. For most people, it is natural to initially oppose the push and turn of the stylist. As soon as the stylist/barber releases the tension, at that one point, our head "bobs" back - because of our natural tendency to oppose the push.

In feeding the stock - as soon as the stock's pressure is released - either because the stock has finished the cut (especially with a resined or slightly dull blade) or because the pressure is released due to the lifting and kicking back, the hand pressure suddenly moves forward on impulse from force that was used in feeding the board. We are NOT expecting the sudden release of resistance, and that resistance is not gradual but sudden. It is this sudden release of resistance between the board and blade that causes the hand to suddenly move forward.

The same as two people pushing on the opposite sides of a door. One person suddenly releases and the other suddenly falls forward awkwardly as the door opens instantly from the pushers motion. As woodworkers, we would love to think that we can control our hand motions better than that, but the fact is, we don't when we are not expecting it. It takes about 1 second to correct the forward force, but the release and forward thrust takes about 1/2 a second at best - plenty enough time for the hand to engage the blade.
This "timing" is where and why this is rarely considered. Most woodworkers don't think that is the problem when it is precisely the problem.

Forward thrust/force by the hand is far more powerful than most even experienced people would think.

[Ed62]

If you're gonna bring logic into the discussion, I don't want to chat any more. Seriously, that makes a lot of sense. Maybe that's the only thing that causes it, and the hand is not actually being pulled into the blade. Thanks for a detailed reply.

Ed

[Stytooner]

Check out this article. The way he describes the accident has relevance in this thread I think.
http://www.myfoxny.com/dpp/news/top-...r-20120121-ncx