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Table Saw Kickback

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Blog entry by MrRon posted 658 days ago 1608 reads 1 time favorited 15 comments Add to Favorites Watch

I have read many posts in several forums regarding kickback and how to prevent it. I read them because I want to get others impressions of why kickbacks happen in the first place. In my 50+ years working with power tools, including saws of all types, I have never regarded kickbacks as a very pressing problem. I get the impression that those who are worried about kickbacks have a basic fear of whirling blades. They can be and are intimidating, but they don’t have to be feared, though they must be respected. Saw blades can be compared with firearms. They both have to be respected for what they can do.

I have used all types of saws; table saws, swing saws, radial arm saws, miter saws and band saws. I have never been cut by a saw blade and can’t remember when I have had a kickback. I don’t have an anti-kickback device (except on the radial arm saw), a reeving knife, blade guard or hold-downs on my saws. I have ripped 4×8 sheet goods on radial arm saws (the most feared operation by most) with nary a blink of an eye. I do use a push stick on my table saw, but have no fear pushing a piece of wood past the blade with my fingers within an inch of the blade. I have analyzed the causes of kickback and trace it back to basic fear and unfamiliarity with power tools and saws in particular. Those who scream safety first and “never get your fingers closer than 6” from the blade” may be a little over cautious to the point of making us paranoid around dangerous machines. Off course, I’m not advocating “throw caution-to-the-wind”; I don’t even want to suggest that you do anything that you are uncomfortable with. I can’t convert anyone nor am I trying to convert anyone over to my way of thinking. That is not my task which is to teach others about the dangers of working with power tools and how to work safely. On safe working, I must emphasize your reliance on working safely without depending on safety devices designed to keep you safe. The most blatant safety device to hit the market as everyone has heard of is the “Sawstop” . It does what it claims, but doesn’t make you a safer woodworker. It only capitalizes on your making a mistake. That mistake, happening on a non Sawstop machine would probably result in serious injury and even loss of some digits. There are two schools of thought when you discuss Sawstop. One school says it creates a false sense of security and the other; it is an insurance policy against injury; either way, any safety device can only do so much. Ultimately the responsibility for your well-being lies with you, not reliance on safety devices or government decrees. I got a little ahead of myself and return to my initial topic, which is kickback.

What is kickback? A piece of wood is pushed into a whirling blade and all of a sudden, without warning, the blade, instead of cutting, decides to grab the wood and hurl it backwards towards the operator. If you are standing directly in-line with the blade, the wood can be kicked back with enough force to inflict damage to person. Most people say, “never stand directly in-line with the blade, but stand to one side” This may be good advice to some, but actually this can be bad advice because if you are standing to one side, you are now pushing the wood at a slight angle. Standing in direct line is the most efficient position for pushing the wood, but more on this later. So what are the reasons for kickback in the first place?

What causes kickback? There are several reasons for kickback and they are enumerated below:

• Saw blade too low: When the blade is set too low (not recommended), the attack angle of the tooth is in a straight back direction, which means all the cutting force of the teeth is directed towards the rear. When the blade is set high (recommended), the cutting force is directed downward toward the table surface. When the blade is set low, the teeth have to cut through more wood than when it is set high. Think: swinging a hammer at the edge of a table and swinging the hammer down at an angle to the top. Which creates more movement of the table?

• Wood not under control: The most important tip is to always keep the wood you are cutting under positive control at all times. When you relax your grip on the wood, that’s when kickback can occur. Don’t be timid about holding the wood. Grip it well and hold it down to the table. I’ve seen people pushing the wood with their thumb without holding it down. (instant kickback)

• Dull blade: When the blade is dull, the teeth tend to “rub” rather than slice or sever the wood grain. A sharp blade severs the grain cleanly. Rubbing causes the blade to slow down and build up pitch especially in the case of resinous woods.

• Pitch and resin build-up: This creates friction, which causes heat to build up, slowing down the motor.

• Fence not parallel to the blade: A fence must be perfectly aligned and parallel to the blade. If it is not, the wood becomes wedged and as the wood tries to follow the fence, the wood burns, friction increases and kickback can occur.

• Lack of power: Most contractor type saws have 1-3/4 hp motors, which is usually adequate for the building trades as they deal mostly with construction grade lumber (softwoods), but when used in the home shops, more demand may be asked of them, such as cutting hardwoods, 2 or more inches thick and cutting sheet goods on smallish size tables. They usually lack the sturdiness of the cabinet saw which has a minimum of 3 hp. The greater power afforded by the cabinet saw enables the user to cut harder and thicker woods without slowing down. The slowing down of the blade which results in burned wood and increased friction which causes kickback is mostly eliminated in cabinet saws, as long as the other points are followed; namely sharpness of blade, parallelism of the fence and height of the blade.

• Wrong type of blade: The wrong type of blade can also cause kickback. A blade intended for a miter saw or radial arm saw with a negative rack can easily cause kickback if used in a saw with the blade below the table. That type of saw requires a blade with a positive rake. The number of teeth is also important. In a rip operation, you want to use fewer teeth. Fewer teeth means there is more open gullet room to hold sawdust. A blade with lots of teeth would clog up quickly while ripping and cause burning. Crosscutting severs the grain and expels the sawdust, although feeding the wood into the blade rapidly can also clog the gullets which are much smaller than in rip blades.

Now that we know what kickback is and what causes it, how can we prevent it? First I doubt that it can ever be completely prevented. There are too many factors to consider. I feel though that developing an understanding of the tool goes a long way. Anyone who has served in the army knows that his rifle is his friend and must respect it. That same respect when applied to dangerous tools will help keep you safe. I’m far from being an expert on saws, or anything else for that matter, but I feel my relationship with dangerous machines is a good one. I hope whoever reads this will see some of the points raised. Safety is our responsibility, not the responsibility of makers of after market devices.

Disclaimer: Because this blog concerns safety, the opinions and statements made are solely the responsibility of the author and not Lumber Jocks.



15 comments so far

View Chris208's profile

Chris208

167 posts in 868 days


#1 posted 658 days ago

While I respect your experience, and your opinion, I would HIGHLY recommend that everyone use any and all safety devices you have available.

Why wouldn’t you? Better safe than sorry, as far as I’m concerned.

View gfadvm's profile

gfadvm

10567 posts in 1289 days


#2 posted 658 days ago

I think you posted a lot of good information here. The worst kickback I ever had was when I first started and didn’t know much. I was told to keep the blade to where it barely penetrated the wood (REALLY BAD ADVICE). It lifted a piece of ply and launched it! No injury, but I had to throw those jeans away!

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View CessnaPilotBarry's profile

CessnaPilotBarry

877 posts in 709 days


#3 posted 658 days ago

What about a closing kerf, when stress is released and there is no splitter or riving knife to keep the wood from grabbing the rising teeth?

-- It's all good, if it's wood...

View Sandra's profile

Sandra

4131 posts in 674 days


#4 posted 658 days ago

Interesting stuff.

-- No, I don't want to buy the pink hammer.

View Grandpa's profile

Grandpa

3047 posts in 1274 days


#5 posted 658 days ago

Good information and well written. Take care of what you have listed and then this other stuff can be added and no one will ever know which one of these saved them from an accident.

View TopamaxSurvivor's profile

TopamaxSurvivor

14589 posts in 2274 days


#6 posted 657 days ago

When you have your first, you will never forget it!

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View MrRon's profile

MrRon

2716 posts in 1842 days


#7 posted 657 days ago

What about a closing kerf, when stress is released and there is no splitter or riving knife to keep the wood from grabbing the rising teeth?

In such a case, you have to maintain downward pressure to keep the work from rising and pushing to force it through the blade. I agree, a riving knife is nice to have as long as it is set up correctly. The important thing here is to maintain positive control of the wood until the cut is complete. If the saw doesn’t have adequate power, you may even stall the blade (not good). In such a case, shut off the saw, but keep maintaining control over the wood so it doesn’t kick back.

View CessnaPilotBarry's profile

CessnaPilotBarry

877 posts in 709 days


#8 posted 657 days ago

I’ve had quartersawn white oak pinch tight enough to tear a Microjig splitter from it’s mount, and on another occasion, become stuck, hard and fast, on the riving knife. In both cases, I held on, shut off the saw, and waited for it to stop spinning.

I honestly don’t believe that I could have held either of those two pieces of stock in place had there not been something holding the kerf open, and would have been pretty much screwed. I’ve been doing this for a long time too, and have the hindsight to admit when the stars aligned in my favor.

I’ve also had kerfs open as I cut, where the side between the fence and blade pushed into the rising teeth.

As far as I’m concerned, a proper riving knife or splitter belongs at the top of the list for preventing kickback.

-- It's all good, if it's wood...

View SnowyRiver's profile

SnowyRiver

51451 posts in 2079 days


#9 posted 657 days ago

I agree with the points made. I do however feel that the fear of a kickback is a good thing. Probably the most often cause of a kickback would be operator error in some form or fashion. There can be other causes though as some have mentioned like the kerf closing on the blade due to stress in the wood. I posted a comment about that just a week or so ago. I know that if I wouldnt have had the riving knife in place then, there would have been a good chance the 3 HP saw would have fired the piece right at me. I learned the hard way. After woodworking since 1968 I hadnt had a serious kickback until several years ago. Yep, it was my fault. I accidently let the piece of wood against the fence drift into the back of the blade as I changed position with my feet as I pushed the board through. The board was only 6 inches wide and about 24 inches long. I can tell you, there was no way I could have held that piece down against the blade. Matter of fact, it hit me before I knew what had even happened. It ripped the heavy duty plastic push stick from my hand cutting the end of the push stick off. It knocked the wind out of me almost knocking me off my feet and it caused a 16 inch long cut on my torso, bruised a lung, and made a huge exterior welt and bruise from my chest near my neck to my belt line. I was somewhat proud of myself though. I had taken a good shot, the best the saw could have delivered and still survived. LOL After the feeling came back in my stomach and chest several minutes later, and after putting an ice bag on the bruise for a while, I continued using the saw to finish the project an hour or so later. I didnt find out about the brusied lung though until the doctor took an XRAY when I went in for a cold a week later. Stupid me though for letting it happen. I’ve installed a riving knife and feel much better about protecting myself now. Am I afraid to run the saw….no. But I do think about this each time I turn it on. Its something you will never forget. I used to be a boxer and was in the martial arts years ago, and no one had ever hit me that hard. The saw and I have an understanding now.

-- Wayne - Plymouth MN

View MrRon's profile

MrRon

2716 posts in 1842 days


#10 posted 656 days ago

Interesting comments. Speaking from experience, I’ve never encountered a situation where a kerf would close up so tight as to prevent completing the cut. I can only think the blade was not the right one to use or it didn’t have enought set. I agree a riving knife is good to have and is a part of a blade guard, but like many, the blade guards are removed for whatever reason and the benefit of a riving knife is lost. When the riving knife is part of the blade guard, it doesn’t compensate for different blade kerfs and is usually a pretty flimsy device. Dedicated riving knives are just coming to the market and are a worthwhile investment.

View CessnaPilotBarry's profile

CessnaPilotBarry

877 posts in 709 days


#11 posted 656 days ago

In my case, both were well known, well regarded, sharp blades. One was a Forrest Woodworker II, the other was a Freud Industrial 24T rip. In both cases, the wood was jointed and surface planed 4/4 quartersawn white oak. Each splitting device was properly sized to the standard, ~ 1/8” kerf blade. There was no way to tell the stock was case hardened before the cut started.

Even if a splitter is too small, it’s better than nothing, as it’ll still prevent reactive wood from completely grabbing the blade. Trying to hold stock in place that is trying to cut 1/32” on each side is far easier than holding something that’s suddenly trying to take a full kerf upward bite with 3+ horsepower.

Really old school woodworkers used to have a buddy stick wedges in the kerf as the rip progressed, to prevent similar issues. This is also why some folks rip with bandsaws.

Glad to hear it’s never happened to you. It’s something that makes an indelible mark on the ol’ experience.

-- It's all good, if it's wood...

View MrRon's profile

MrRon

2716 posts in 1842 days


#12 posted 655 days ago

Bad things do happen when we don’t expect it. I have had one kickback, but don’t recall having anymore. It was caused by my own stupidity and carelessness. I guess that taught me to be more attentive to what I’m doing. Try ripping with a RAS. I did it a few times and I can tell you it’s not for the faint of heart. I do all my ripping on the table saw, but I never try to wrestle 4×8 sheet goods on a table saw. I always cut them down to size with a portable saw and guide.

View Ayala's profile

Ayala

7 posts in 1093 days


#13 posted 641 days ago

Fear has a great deal with kick backs, but it also has a lot to do with the operator. Im 18, and while in high school, I sliced my middle finger on the table saw. I was helping a student reveive on the table saw, and he let go of the borad even though more than half of the board was still on the table, causing us to have kickback. The good thing was that we had a blade gaurd, if not my whole finger would have been gone. Thankfully that has been the only kickback I have had, and I hope the last. The trip to the ER was not exiting.

-- I may be a girl, but I can still wood work

View jacktheripper's profile

jacktheripper

7 posts in 1945 days


#14 posted 629 days ago

You obviously work with better wood than the home depot pine I ripped for 20 years at woodworking shows. Many woodworkers have shown me their scars and missing fingers from the kickbacked boards.
A piece of that stuff can pinch the blade hard enough to stop a saw blade well before it gets to the riving knife.

Watch out ripping a board with a knot within a foot of the end of the board.

When you get to any rip you don’t feel comfortable with- use a feather board or hold down spring. A hold down feeder wheel will keep that board from climbing up the blade and getting thrown back at you.
I have tested hold downs and rip feeders for 20 years at woodworking shows from Florida to Vancouver and never had a kickback using springs instead of fingers to control the wood.
Clamp on your own hold down or use a fast setup one like the magnetic ones I demonstrated.
Keep your fingers for more important jobs.
Jerry

View TopamaxSurvivor's profile

TopamaxSurvivor

14589 posts in 2274 days


#15 posted 629 days ago

Thanks for the insight Jerry. Lots of things to think about based on your 20 years of experience.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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