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Kickback #1: So How Fast Does That Piece of Wood Launch from the Table Saw?

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Blog entry by Chris Moellering posted 10-09-2012 05:43 PM 2574 reads 1 time favorited 12 comments Add to Favorites Watch
no previous part Part 1 of Kickback series Part 2: Table Saw Kickback Part II »

Since I bought my first table saw about 6 wees ago, I have managed to keep all my fingers firmly attached to my body. I did managed to get smacked by the off-cut that kicked back once leaving a bruise on my forearm.

This got me to wondering, “How fast does a table saw launch wood?”

Well, my saw says it runs at 5,000 rpm.

It uses a 10” blade.

So, the circumfrence is 31.4” (10×3.14)

So, if it was a wheel, it would be moving at 157,000 inches per minute. (31.4×5,000)

That’s 13,083.33 feet per minute. (157,000 / 12)

Or 785,000 feet per hour. (13,083.33×60)

Which comes out to 148.7 miles per hour. (13,083.33 / 5,280)

That’s the maximum theortical speed, not taking into account drag and other factors.

No wonder it left a mark. ;o)

-- Grace & peace, Chris+



12 comments so far

View a1Jim's profile

a1Jim

112486 posts in 2294 days


#1 posted 10-09-2012 05:50 PM

That’s really something, now we have to get a radar gun and confirm the speed for sure. :)) Who knows it might become a new category in the Guinness world record book ? Only one problem, who gets to create the kick back ???

-- http://artisticwoodstudio.com Custom furniture

View BTimmons's profile

BTimmons

2163 posts in 1202 days


#2 posted 10-09-2012 06:24 PM

The Mythbusters fan in me says use a high speed camera. I’m pretty sure you’ve got a theoretical top speed worked out, but any piece that encounters kickback will move slower than that depending on how it’s hit and what it weighs.

And no, I wouldn’t want to stand in the way to test that. That’s what they have Buster for.

-- Brian Timmons - http://www.BigTWoodworks.com

View WhoMe's profile

WhoMe

1124 posts in 1961 days


#3 posted 10-09-2012 07:03 PM

Well, another mystery of the universe solved….lol

Since I have been fortunate to have had only 2 kickbacks and neither impacted body parts, I never thought of trying to figure out how fast it might have been going.
That makes me all the more careful and use all the safety equipment and common sense I can.

-- I'm not clumsy.. It's just the floor hates me, the tables and chairs are bullies and the wall gets in the way.. - Mike -

View cabmaker's profile

cabmaker

1311 posts in 1526 days


#4 posted 10-09-2012 08:16 PM

Chris, I am sorta nervous for you. How did you manage to get an offcut launched at you ? Good luck !

View Grumpymike's profile

Grumpymike

1149 posts in 1033 days


#5 posted 10-09-2012 08:49 PM

Chris, sit down, take a deep breath and think about this … ya got to much time on your hands, ... Now, go to the shop and make something, with out the calculator. ;)

-- Grumpy old guy, and lookin' good Doin' it. ... Surprise Az.

View derosa's profile

derosa

1557 posts in 1553 days


#6 posted 10-09-2012 08:55 PM

It moves fast enough to partially crack an asphalt block with a small piece of purpleheart. Made me very glad I wasn’t standing in the way.

-- --Rev. Russ in NY-- A posse ad esse

View NormG's profile

NormG

4359 posts in 1721 days


#7 posted 10-09-2012 10:20 PM

I’m submitting to Myth Busters for confirmation

-- Norman

View bullhead1's profile

bullhead1

228 posts in 966 days


#8 posted 10-10-2012 02:53 AM

I can add some more info for your calculations. My first kick back came back and hit me in the chest and laid me out flat. I was 5’ 9” and 180 pounds and standing approximately 1 foot from the table. I can’t remember which direction the wind was coming from but I know the sun was not in my eyes. I just know I was stupid and pushing the board through with pressure left of the blade. Once you have a kick back like that you never forget about it.

View Monte Pittman's profile

Monte Pittman

15060 posts in 1055 days


#9 posted 10-10-2012 03:18 AM

The piece that got me left a bruise and split the skin on my chest. I had a heavy shirt over a T shirt. I would hate to think if I had less on.

-- Mother Nature created it, I just assemble it.

View TopamaxSurvivor's profile

TopamaxSurvivor

14991 posts in 2393 days


#10 posted 10-10-2012 03:39 AM

AS I recall, that speed sounds about right. Fortunately, I was standing to the side when a 2×4 struck the wall behind me. I don’t recall exactly why it happened, but I’ll never forget the lesson learned.

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

View Chris Moellering's profile

Chris Moellering

224 posts in 1366 days


#11 posted 10-10-2012 10:39 AM

I looked a bit at formulas for angular inertia and such last night, but it was more than my 20-some year-old high school physics skills could grasp. Otherwise, one could do a better calculation figuring in the mass of the piece being “shot.”

I don’t remember the details on how I managed to shoot myself. But I know I haven’t done it again! Since then I’ve added a sled and a featherboard, both of which help in their applications.

-- Grace & peace, Chris+

View Tootles's profile

Tootles

719 posts in 1219 days


#12 posted 10-10-2012 11:05 AM

An interesting calculation as a theoretical top speed, but I think it is probably quite a lot less.

I worked backwards from the power of the saw (ignoring losses and inefficiencies). I also had to assume a duration of “contact” between the wood and blade during the kickback in order to calculate the energy transferred (E = P * t). So with a 3kW saw spinning at 5000 rpm, I calculated that a 5 ounce piece of wood (i.e. the weight of a baseball) that was in contact with the blade for 1 revolution would be kicked back at “only” 48 mph.

The speed increases as saw power and contact time increases, but decreases as the weight of the wood increases. The relationship follows a square root curve – it is not linear.

Of course, I could be completely wrong. I didn’t get much sleep last night and haven’t eaten well today so my head is particularly fuzzy at the moment. I’m sure there will be someone smarter than me who will correct me if I am mistaken

-- I may have lost my marbles, but I still have my love of woodworking

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