Now that's a kickback!

[LarryC]

Rick Christopherson said:

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If you had not been using a push stick on such a wide rip, the tilted blade would actually have slowed this down enough at the beginning to regain control and get the leading edge of the board back into the fence.

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I'm glad you mentioned this, I was just thinking to myself after reading this thread that I don't usually use a push stick unless it's narrow stock to begin with. While I know it's risky sometimes to use your hands, that's how I do it (again with wide enough stock.) Might explain why I haven't had a nasty kickback yet...

[RolHammer]

Humanbackhoe said:

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All of my processes are currently under review and I appreciate the input.

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Dude! I'm happy you (or the pooch outside) weren't hurt!

Whatever the cause(s), the statement above shows that in addition to retaining all ten fingers you stayed in possession of two other critical things - your nerve and the head on your shoulders! I dunno about anyone else but if something like this'd cooked off in my shop, it'd be with some understandable trepidation that I reached for the power stud the next time 'round. But, most importantly there's no 'Well I done this like a hunnert times an' she's never run south 'o me before. 'S no problem with my skills or techniques, I's just unlucky is all.' You're manning up to the situation, trying to find out exactly what caused it to head into the crapper and putting all of your procedures under review.

This, more than anything, is probably the most valuable thing about the thread - you serving as a positive role model this way.

In addition to that it was fascinating - as always - to see another myth dispelled by Rick-meister. I thought, like many others, the bevel-to-fence-is-bad thing was gospel. Interesting to see I wrong and happy to know how to prevent becoming a victim...

About the splitter - whether or not it would have prevented this particular situation (from reading through this, I suspect it probably would have), I suspect it would have been the anti-kickback pawls attached the splitter that would have prevented the stock's sudden jump to hyperspace that made this so dramatic. So, during your procedural review, please do consider regularly using a splitter and blade guard...assuming you don't already and this was just an anomaly.

And as to not using push sticks on wide cuts, Rick's definitely made a convert out of me on this point! He makes a very convincing argument that's hard to refute.

Many happy, healthy and safe years of woodworking to you!

[Jason/Woody]

Holy WOW!!! My dad had a kickback about 2 months ago on a new saw he just bought. He was off a little to the side, but not enough. He was trimming down a board for a portable kegerator he was building, and the narrow strip got caught by the blade at the end of the cut and shot at him like an arrow. He had a nasty bruise about 8" from his, well, you get the idea lol. I was surprised to see your picture though, that is a launch, not a kickback. Glad you are ok though. I bet your heart was pounding

[Rick Christopherson]

Humanbackhoe said:

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I can get one for you. It is a common plastic handled one with a 3/4" notch, about 10" long. It is not the one that lays on top of the board with a little heel that engages it.

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Let me start with this topic first because it is the easiest. To put it short and sweet (or not so sweet) this is the absolute worst type of push stick you can use. There are many reasons, but the biggest one is that it removes too much control over the workpiece from your hand. Because of the distance between your hand and the workpiece (i.e. the length of the stick) it is too easy for your hand to move downward or forward against your intentions. I have a friend here locally that took a nasty cut across the finger because this was the type of push stick he was using when a kickback occurred, and the result of his normal pushing force resulted in his hand going forward and downward into the blade, while the push stick somersaulted below his hand.

Use one that gives you more direct control over the workpiece, and do not use one when it is not necessary.

Humanbackhoe said:

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Thanks for the response, Rick, the gullet trough was at the height of the top of the board, if this is too low, how much higher should the blade height have been?

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Technically, the gullets have nothing to do with blade height, but I typically don’t argue the point very often, because at least people are getting the blade a little bit higher. The problem with this “gullet-height” rationale is that the gullets are going to vary from blade-to-blade, and for different types of blades.

Unfortunately, it is the blades that need to be raised a little higher are also the ones that typically have the shallower gullets. So that is why this rationale is not the best--but at least it is a start.

It is really hard to put a number on a desired blade height, but in most cases, I simply look at the blade and know from instinct whether it is too high or too low. I don’t really even pay attention to it while I am setting the height. (I guess I have been doing this too long.) It is really dependant on how hard the blade needs to work to get through the cut. The harder the blade needs to work, the more inclined I will be to raise it up some more.

A bevel rip is a perfect example. Instead of cutting through 3/4 inch of material, you are cutting through an inch or more. That’s going to make the blade work harder. However, there is a trade off, in that you don’t want the blade to be so high that it poses an undue safety concern.

For a bevel rip as wide as yours was, I would have raised the blade so that at least 1-1/4 inches was exposed on the sloped side of the blade. If it was a narrower rip, I would have reduced this slight because my hands would have been closer to the blade.

The best way to answer this question is to try it out yourself and see how the blade reacts to the various cuts (i.e. how hard do you need to push to feed the stock.)

[Rick Christopherson]

Lumber Yard said:

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Rick,
Once the board on a trapped bevel cut starts to rise on the back side it is gone because the the long part of the material is thrust into the short distance of the blade.

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The key to this, is that the blade plate itself actually serves a little bit as a riving knife (in a way) because the middle of the board cannot deflect sideways through the blade plate without literally bending the blade sideways.

Oh that reminds me: Humanbackhoe, check your blade for lost teeth or other damage, because it is very, very likely that the blade was deflected into your saw's throat plate.

Uhhh, where was I? Oh, with the blade plate resting over the top of the workpiece, it actually helps prevent the back of the board from lifting up, which is a necessary action before the kickback can fully occur. If you react fast enough to this situation, you would find a trough in the side of the board which is equal in depth to the difference between the blade teeth and the blade plate.

If you go back and look at the first picture posted, you will notice that the angle of the bevel around the area where the wood finally split is no longer 22.5 degrees. This is because the blade was heeled over by the forces.

On a left-tilt blade, the only thing stopping the blade from rising in the rear is the amount of downward force applied by the operator. Contact with the blade plate and/or teeth actually help lift the workpiece instead of trying to keep it down.

In most cases of this type of rotational kickback, you will notice a distinctive gouge in the back of the workpiece, but this is the first time I ever recall seeing someone post a kickback picture with complete cut-through for the entire length of the kickback. That is because the blade plate prevented the workpiece from lifting. And unfortunately, that is also why this one was so violent.

I am going to continue this in another posting, because something else just occurred to me about Humanbackhoe's methods.

[Rick Christopherson]

Humanbackhoe,
While I was writing my previous response, I noticed something in your pictures that I failed to take note of the first time around. I was in awe from seeing a kickback picture with a complete cut-through, that I didn't notice that you had actually finished your cut before the kickback occurred. Sorry, but this is not going to be good.

The significance of this is that the sawblade was no longer "trying" to take control of the workpiece away from you, but instead, you simply "gave up control" without a fight.

Now this still ties back into what I was saying about the push stick, but actually amplifies it a bit more. If the blade didn't take control of your workpiece, that means that you didn't either. The blade didn't pull the workpiece askew--your push stick pushed it askew.

Most push sticks, especially this type, do not provide any "yaw" control over the workpiece, so if your pushing point was right-of-center, then you actually begin the rotation necessary for this type of kickback to occur, and do not have the yaw control to pull it back

The lesson to be learned here is to always maintain complete control over the workpiece. If you do, then 90% of all kickbacks would never happen.

[Alan S]

Rick:

Wouldn't a splitter have prevented this? It seems to me that the workpiece pivoted around the corner as it was sucked back under the blade, until as you point out the upward force bent the blade out of the way and threw the piece. Wouldn't a splitter have prevented that original pivot?

[Lumber Yard®]

Rick,
I agree with what you are saying as far as technique and causes in this instance.

However saying that a trapped bevel cut is safer than a cut with the blade beveled away from the fence is just not the way I see it. You even say that if a kick-back were to occur that the kickback is much more violent on a trapped bevel cut. A kickback although possibly more likely with an "untrapped" bevel cut is just going to be significantly less problematic for you, the saw, and your property.

I think all the advice given here is valuable and I have really listened to your argument but I still believe given a choice an "untrapped" bevel cut is safer. We are human mistakes happen in our techniques and set-ups. Given the choice I'll take the increase in probability with an "untrapped" cut vs. the severity of a "trapped" cut.

[Humanbackhoe]

Rick,
Your process of observation and understanding of dynamics are appreciated. I did not have good control of the board. A hand on the wood instead of flimsy pushstick would have been the way to go. There is no defense of my actions. This happened so fast I did not see it, therefore this cut should have been thought through more completely first, if I "gave up control without a fight" it was in the planning stage. That was actually the forth cut with that set up I had done today. You are dead on about the lack of "yaw" control. It seems that putting my hands closer to the blade is, in some cases, safer.

[Rick Christopherson]

Humanbackhoe said:

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Rick,
Your process of observation and understanding of dynamics are appreciated. I did not have good control of the board. A hand on the wood instead of flimsy pushstick would have been the way to go. There is no defense of my actions. This happened so fast I did not see it, therefore this cut should have been thought through more completely first, if I "gave up control without a fight" it was in the planning stage. That was actually the forth cut with that set up I had done today. You are dead on about the lack of "yaw" control. It seems that putting my hands closer to the blade is, in some cases, safer.

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Hey, just breath a sigh of relief that you are not getting a bill from me. The last time I did an analysis it cost the defendants $25,000, and that was my bill, not the award.