Your kickback experience

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Upscale said:

I've been known to rip 2 1/4" strips from 8 foot 2x10 SYP boards. Built my workbench this way, cut them apart, glue them back together. (Sounds crazy, I know.)
http://www.thevideodoc.com/Images/WorkBench01.jpg
But the amount of reaction wood contained in these 'veneer cores' was amazing. Big, sappy, pinching things. They did smell good when cut, however - kinda like Christmas. Didn't try letting the blade burn, or I could have had a forest fire odor as well.
My wimpy little saw barely cut it, much less left enough power to throw it too far. Two more HP would have made a different in this scenario, I fear.
On the average furniture project, no, it probably wouldn't have differed a whit.
Greg G.
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I find that with more HP the saw and the sharp blade are more likely to cut the wood thather than catch it and throw it back. Its the under powered saws that require you ro finess the wood through with a light hand that tends to catch and throw the wood.

My experience with the more powerful saw is that it indeed does not jam or stall nor with a firm grip does it rip it outta there and send it flying. My experience with more power and a firm grip the blade simply cuts in another direction. Similar to a hot knife cutting into room temperature butter I find less resistance with a change of cutting direction which normally leads to a kick back.

Do not fear the sharp blade. It will more easily cut your wood rather than catch the wood and throw it back than a less sharp blade. Additionally, fingers will cut off just as easily with a blade that has had all of its carbide teeth broken off . I have been there and done that. Fingers are MUCH softer than wood. ;~)
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Greg G. wrote:

Machines are alive. They never apologise. If you're scared of them, they will sense it and bite. If you respect them, They will respect you. If you treat them well, they will treat you well. If you let them work at their own pace, they'll work forever. If you push them, they'll push back and eventually jack up. Machines are always happier doing the job they were designed for. and finally You only shake hands with a Power House once. :)
regards John
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John B said:

John,
Perhaps 'scary' wasn't the correct term - used mostly for drama. I did pop it on there and saw away - not leave it in a drawer for six months or anything... ;-)
But nevertheless, the vision in your mind's eye of that blade sawing through your fingers - the 'what if' scenario - was enough to send a shiver up your spine... Kind of like the rush you get looking down from the top edge of a really tall California cliff...
And as for your dad's advice, he's absolutely right. With the notable exception of forever part... ;-) Things aren't what they used to be... (I grew up around whirring machinery and coursing electrons.)
Greg G.
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Greg G. wrote:

It's funny how the old mind can conjure up the worst scenario sometimes. You may have done a job a hundred times and not given it any thought, then suddenly, there's a "What If". When it happens to me, I often have to leave what I'm doing for something else and then come back to it when things have settled down. Have a good one John
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Hmmmmm... My compound bow will launch an arrow at somewhere above 240fps. That translates to around 160mph if I do the math correctly. It won't come near to putting an arrow through a 3/4in piece of plywood from any distance. I have to confess, I've never tried to put it through a piece of wood at 5 yards, but I have hit a target frame or two over the years at 20 yards and penetration is only an inch or two. A six foot piece of 1x1 will surely have little enough spine to distort upon impact and just makes me have to question its ability to penetrate a piece of plywood any amount at 5 yards, let alone penetrate it three feet.

Likewise, I've never used a guard or a splitter or pawls for roughly the same period of time. It's not that I wouldn't use them, but I've never had a saw with them. Kickback is a very real consideration, but I have argued in the past, and continue to believe that kickback is something that should be understood in order to be dealt with, and not something that one attempts to avoid by blindly placing faith in adjuncts. We see enough posts here on a regular enough basis, where the author is saying "gee, I had all of the safety equipment in place and I got a kickback - what happened?". Sometimes we get complacent with the gear that is on the tools and we let our guard down when it comes to the basics.
--

-Mike-
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On Fri, 4 Nov 2005 05:17:24 -0500, "Mike Marlow"

the physics involved look something like this: your compound bow is human powered. you can never put into it more than about 1/3HP. it stores a bit and releases it progressively, but I doubt that it's applying more than that 1/3HP. this is why your arrows are so light- otherwise they wouldn't be able to go so fast.
a longbow shoots a heavier arrow, but it takes one very strong guy to draw it. a longbow was supposed to be able to penetrate chain mail- it'd probbly penetrate 3/4" plywood.
crossbows usually are too high a draw to be pulled by human arms. they are mechanically cranked, and shoot an even heavier bolt. they would penetrate plate armor. prolly not even slow down much through plywood.
my tablesaw is 3HP. it can launch a chunk of wood approximately 9 times as heavy as your bow can shoot an arrow, as fast. that is a lot more energy being delivered to that piece of plywood.
I don't know if it would penetrate 3/4" plywood in a kickback. I hope I never find out.
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snipped-for-privacy@all.costs writes:
[...]

Power does not come into this calculation, but force. (Power as in energy per time, energy as in force times path length) Also momentum (mass times speed) is an issue.
--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
mailto: snipped-for-privacy@physik.uni-bonn.de Phone: +49 228 73 2447 FAX ... 7869
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Phone: +49 228 73 2447 FAX ... 7869

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"Velocity" is simple -- blade circumference, multiplied by RPM. For a standard 10" saw, you're talking about a circumference of 31.416+ inches. At 3600 rpm, this works out to a rim speed of a bit under 120MPH. The HP rating is irrelevant, as long as it is 'enough 'to spin the blade at the indicated speed.
A kickback is going to accelerate to "approximately" the speed of the blade.
"Force" depends on the mass of the object being thrown. and how fast it gets up to speed.
At a _blade_speed_ of 3600 rpm (60 rev./sec.), and postulating (value pulled out of thin air) that the kicked-back piece binds to the blade for, say, just under 1/8 of a blade revolution, the acceleration period is roughly 1/500 of a second. going from zero to 120mph in 1/500 of a sec. is an acceleration of about 75,000 ft/sec/sec.
One horsepower is, my calculator tells me, equivalent to 17,600 ft-lb/sec. ft/sec/sec.
Which, if I'm doing the math right, will impart the above-mentioned "120 mph" velocity to a roughly 1/4 lb mass.
2 hp, 1/2 lb. 3 hp, 3/4 lb. 5 hp, 5/4 lb.
If the kicked back object is heavier, just reduce the 'final velocity' accordingly.
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When I was a junior in high school, a senior got a nice kickback that sent a 4 foot long piece of 3x3 stock into his chest like a javelin. Bruised his sternum and knocked him about 4 feet back. Dude had a 65 inch chest, so this was no willowy kid.
I had already had a few kickback experiences before that happened. The first one occured when I was in junior high school screwing around with my old mans table saw. I was pulling something through the back side with the blade guard off when it twisted and threw my finger into the blade. I cut halfway through the first digit of my left hand middle finger. It was cut exactly halfway through and if the blade had been any higher than a half inch above the thickness of the stock, I would have lost the entire tip of the finger, which incidentally would have made my index finger, middle finger, and ring finger all exactly the same legnth, lol.
The other one happened my freshman year of HS when I got a kickback on the big old 12 inch RAS. Somehow it managed to kickback away from me and flew into the wall behind the RAS snapping off the wooden fence and makign a hell of a boom.
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wrote:

I had ONE, when I was a beginner, on a CROSSCUT! 8^(
I had recently learned how to use the fence as a gauge for multiple crosscuts. The correct way to do this requires a stop block clamped to the fence that ends well before the front edge of the blade.
A few weeks later, I used the technique again, but forgot the stop block. An approximately 8" long x 1" x 4-5" wide piece of 4/4 red oak got fired into my kidney area.
The initial pain was so bad, I though I would die within the hour. I've taken ridiculous mountain and road bike spills, played organized, full-contact hockey, totaled cars and trucks, put my hand through 12" radio control propellers... NOTHING hurt like this. They didn't even make me wait to be examined at the emergency room.
Fortunately, the wood had hit my right hand (which took a few more minutes to start to hurt) on the way to my body, so no permanent damage was done. I don't want to think about what a direct hit might have done.
Always think through a cut...
Barry
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Those of us who learned to stand out of the way when ripping and to let it fly when in doubt have had few, if any injuries, I'm sure.
Now the wall has suffered a few indignities from ripping poplar (real poplar) and wood from right at the heart of the tree, but not even my wooden fingers were damaged.
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Snip

IMHO standing to the side and letting the wood fly by is part of the problem. I have on several occasions had the wood fly by while I was not in the line of path of the blade and have been hit. Again, IMHO it is when you do not have a FIRM hold and let go of the stock that the kick back has the opportunity to develope. The push sticks that simply allow you to push the stock through from the back edge of the stock scare the hell out of me. You have to keep the stock down on the table surface to prevent it from flying back. With out downward pressure there is nothing to keep the board from lifting and possibly kicking back. I have often had the stock start to lift up and I simply push back down. Often the piece is damaged but the wood stays on top of the saw. I find that with a firm hand or with the use of a push stick that allows you to apply downward pressure along several inches of the wood so that the blade simply cuts a gouge rather than kicking the wood from the blade keeps the situation from developing.
And to go a bit farther,;~) Many believe that a more powerful saw is likely to do more harm. Again IMHO and with my experience a saw with a dull blade and or less power is more likely to kick back than one with more hp and a sharp blade. I had many more close calls with my old Craftsman with the 1 hp motor than my Jet with the 3 hp motor. I believe that when cutting stock that was a challenge for the saw that I would handle the stock with a lighter grip/touch to prevent stalling the motor. The light hold on the wood would often present a problem. With 3 hp I always have a firm grip and easily push the wood back down to the table surface should it begin to raise up. With more power the blade simply cuts a new path rather than grab and throw the wood back with that light grip.
IMHO being in position to firmly hold down the wood and learning to deal with and not panic during a developing situation that would lead to a kick back is better than trying to keep out of the way.
Do not procede with any procedure that you would feel unsafe in doing.

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Well, the very best way to avoid danger is - to avoid it. I'll say that with out qualification. If you're not there, you can't get hit. If you haven't seen the classic body positions from the basic woodworking literature on how to rip on a tablesaw, look at them. Good information.
And letting go is a great option in my opinion, it's one that I developed by reading accident reports in my former job, where most fatalities were from delaying ejection (trying to salvage something) until out of the envelope. When it doubt - punch out.
I'm not going to risk my fingers for _any_ piece of wood, I don't care if it's ebony. Nor would I recommend it to anyone else.
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I think what Leon is saying George - and I agree with it, is that better control and observation will result in fewer kickbacks. Kickback is not something that is "going to happen". It does not have to be a part of your woodworking endeavor. Standing off to the side positions the operator to be in less control over the workpiece and increases the likelihood of kickback. Kickback is not magic - it is very predictable and very observable. Good practice makes a better preventative measure than adopting postions that lessen your control and observation of what's taking place.

I'm not in favor of letting go. That guarantees the outcome. Why let go when controlling the piece will result in an incident free cut? There's quite a bit of difference between controlling a cut to prevent a kickback and punching out of an airplane. Though at some point one could certainly draw an anology between a jet and an errant piece of wood...

Yeah - but that's not at all a part of what's being discussed. I'll take it one point further and say that I'm not about to willingly let a piece of wood go ballistic when I possess the ability to control it through the cut and to a restful place on the other side of the saw blade.
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I was cutting 1/4 flooring on my RAS, the finish was too slick for the anti kick back pawls. it threw the piece at me and hit me 2 inches right of the family jewels, tearing my leather apron and blue jeans on its way. Didn't break the skin but I had trouble sitting on my orange size balls for a long while.
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"Mike W." wrote:

...
In roughly 30 yrs I've never experienced any instance of severe kickback.
I do not use the TS splitter.
My only real conscious practice is to routinely push _everything_ completely through and take offcuts away immediately and to ensure blade is at proper depth to clear surface.
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On Fri, 04 Nov 2005 08:04:04 -0600, Duane Bozarth

Duane, I'm with you, in 35 years I've never had anything like severe and I don't use the splitter. But I can still remember the first day of instruction on the TS in woodshop. Took 4 years in it with the same instructor, Mr Norman. A skilled woodworker with all digits he did not tolerate safety infractions at any level, from cluttered work areas to improperly maintained equipment. You didn't follow safety procedures you would never finish the class. Before turning on any equipment you had to pass a written exam on safely using it. Turning off equipment when a power outage happens is ingrained in me. Its like my military serial number.
Like you I try and make safety a conscious procedure. Because there is always a first time. My good shop buddy lost a thumb with his TS and he is just as safety conscious as anyone. Just needed to make one crosscut on a small piece of pine, he didn't take the 2min. to walk over and grab his sled and put it on. Why, he was going to rip a bunch of oak and thought he could handle the crosscut and save a few minutes. Just one time and one thumb. Ed
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On Fri, 04 Nov 2005 08:04:04 -0600, Duane Bozarth

My only kickback was a badly executed crosscut. <G>
Barry
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