Tablesaw chucked a scrap piece my direction.... - Page 2 - Woodworking Talk - Woodworkers Forum
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post #21 of 39 Old 12-15-2015, 02:35 PM
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Just in case you need some entertainment and would like to see some serious 2x4 action. Google around for Survival Research Labs and take a look at The Pitching Machine. As originally set up, it used a Cadillac Eldorado engine to throw 6' 2 x 4's about 1/sec on full auto and at approx 200mph.
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post #22 of 39 Old 12-15-2015, 03:43 PM
where's my table saw?
 
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Like I said in Safety Tips Thread ...

Quote:
Originally Posted by Robson Valley View Post
No, man, I didn't get the chance to finish the cut.
Maybe a 24" piece, half cut before the low blow.
Happy to say that I'm not shooting blanks.
Most kickback occurances/accidents don't get reported because there is no blood and no stitches are required, BUT they can be near fatal. A mill operator with years of experience, I know got speared in the gut by a tablesaw kickback. It was serious and he had a long recovery period. Like they say in motorcycle riding ...if you haven't crashed yet, it's only a matter of time. If you haven't had a tablesaw kickback, it's only a matter of time.

Fortunately, blood spilling and tablesaw amputation accidents are far and few between.

My guess on the kickback described above it was a blade pinching incident, and the workpiece rose up and over the blade and was propelled toward you. Splitters are used to prevent this type of occurrence as well. I didn't use a splitter for years and then I understood their function and reason for being. Now I always use mine whenever possible.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #23 of 39 Old 12-15-2015, 04:06 PM
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Yeah, I didn't know what those things were for until I bought my own TS (Ryobi $100) and was tempted to take it off. I do for short cross cuts. However, when I cut 100 birch blanks 7/8" sq x 14" for wood carving spoons & forks, that "riving knife"(?) was snugged up tight. I cut the 6/4 birch to 14" and then rip a pile of that. 70 spoons and 30 forks and I don't care if I ever carve another one in my life.
In any case: don't stand in the line of fire.
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post #24 of 39 Old 12-31-2015, 07:33 AM
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I've got a Craftsman 8" 1950's era table saw that the previous owner replaced the old motor w/a 2 hp motor. It does me a good job, no bigger than it is. I don't have a need for a huge table saw, but use this one regularly. No, it doesn't have a splitter, or a blade guard, or anything else safety minded on it. It has its purpose, & that's that. There's things I do with my saw that I wouldn't allow anybody else to do, simply because I trust the saw, & stay out of the line of fire. Make no mistake, That ol' fella has given me a kick back or two, but nothing serious. I still have all my fingers! Table saw safety is something that is often forgotten about until an accident happens. Learn to respect that saw. There's spinning teeth in one end of it!!
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post #25 of 39 Old 01-01-2016, 06:32 PM
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Given the motor rpm and the 10" blades, I worked out that the rim speed is 180mph. While I don't believe that the 2x4 came back at me at that speed, it was fast enough to get my full attention.

What was worse, though, was a TC tooth coming off a 10" blade and drilling me in the forehead.
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post #26 of 39 Old 01-01-2016, 06:49 PM
where's my table saw?
 
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show us your math

Back when I came up with this:
A table saw blade at 4000 or so RPM with a 10" blade has a peripheral speed of 4000 x pi D or 125,600 in per min divided by 12 equals 10,466 ft per min. divided 5280 equals miles per min. times 60 equals 118.93 MPH. FYI

Another site, Lumberjocks, came up with this:
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)

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #27 of 39 Old 01-02-2016, 12:42 AM
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Seriously woodenthings? Show us your math? The man was just trying to make a point, not impress us w/his mathematical skills. I thought this thread was about table saw safety? You made your point.

Sawdust 703
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post #28 of 39 Old 01-02-2016, 12:46 AM
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Woodnthings, you need a TC blade tooth embedded in your forehead to comprehend the issue. They are a whole lot bigger than you think. Bring your own bandages.
My saw cranks 5,800rpm, the last time we checked it with the strobo tachy.
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post #29 of 39 Old 01-02-2016, 01:41 AM
where's my table saw?
 
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not questioning your post but

The 180 MPH was different from what I calculated, so I wanted to know why? The 5,800 RPMs was what made the difference. So, for the fun of it I wanted to know what 180 MPH was in Ft Per Sec, something I can relate to from my knowledge of rifle and handgun ballistics. Turns out to be 264 Ft per sec., about the same as a decent compound bow: http://www.answers.com/Q/What_is_180...eet_per_second


Also for reference about the same as a lever action Red Ryder Daisy BB gun:
The traditional, and still most common powerplant for BB guns is the spring piston, usually patterned after a lever-action rifle or a pump-action shotgun. The lever-action rifle was the first type of BB gun, and still dominates the inexpensive youth BB gun market. The Daisy Model 25, modeled after a pump-action shotgun with a trombone pump-action mechanism, dominated the low-price, higher-performance market for over 50 years. Lever-action models generally have very low velocities, around 84 m/s (275 ft/s), a result of the weak springs used to keep cocking efforts low for use by youths. The Daisy Model 25 typically achieved the highest velocities of its day, ranging from 114 to 145 m/s (375 to 475 ft/s).[citation needed]
https://en.wikipedia.org/wiki/BB_gun

I guess you are lucky to still be alive or still have your vision after that. As to what you could do to be more safe, which is the topic being discussed ..... nothing that I can think of.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 01-02-2016 at 02:39 AM. Reason: added BB gun data
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post #30 of 39 Old 01-02-2016, 09:26 AM
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Quote:
Originally Posted by woodnthings View Post
. . . As to what you could do to be more safe, which is the topic being discussed ..... nothing that I can think of.
I can think of something: Don't use carbide blades, because they have the potential to have a tooth break off if it hits something hard. On all-steel blades, the teeth are integral to the blade versus being brazed on.

Mind you, as we all know, Carbide blades stay sharper WAY longer and are less likely to be damaged by overheating under heavy load or use of too high a TPI blade for the task at hand . . .

Jim G
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post #31 of 39 Old 01-02-2016, 10:28 AM
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Quote:
Originally Posted by JimGnitecki
I can think of something: Don't use carbide blades, because they have the potential to have a tooth break off if it hits something hard. On all-steel blades, the teeth are integral to the blade versus being brazed on. Mind you, as we all know, Carbide blades stay sharper WAY longer and are less likely to be damaged by overheating under heavy load or use of too high a TPI blade for the task at hand . . . Jim G
I can think of something. Don't use a table saw. Problem solved.
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post #32 of 39 Old 01-02-2016, 10:37 AM
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The circumference of the saw blade is 31.4159 inches. Any point on that circumference travels that distance times 5,800 in a minute or 182,212 in per minute. For one hour that is 182212*60 equals 10,932,720 inches in one hour. Inches in a mile equals 12 times 5286 or 63,432 inches per mile. 10,932,720 divided by 63,432 or 172.3533863034431 mph.

Not that it makes a hill of beans because that velocity is not the speed at which a piece of scrap would be expelled. Too many other variables influence that.

I doubt that there is no one who has ever used a power saw of any type who has not had a piece of scrap thrown at him/her.

George
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post #33 of 39 Old 01-03-2016, 07:54 AM
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Quote:
Originally Posted by GeorgeC View Post
Not that it makes a hill of beans because that velocity is not the speed at which a piece of scrap would be expelled.

George
The scrap, no. But a rogue carbide tooth possibly.
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post #34 of 39 Old 01-03-2016, 09:06 AM
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Quote:
Originally Posted by GeorgeC View Post
The circumference of the saw blade is 31.4159 inches. Any point on that circumference travels that distance times 5,800 in a minute or 182,212 in per minute. For one hour that is 182212*60 equals 10,932,720 inches in one hour. Inches in a mile equals 12 times 5286 or 63,432 inches per mile. 10,932,720 divided by 63,432 or 172.3533863034431 mph.

Not that it makes a hill of beans because that velocity is not the speed at which a piece of scrap would be expelled. Too many other variables influence that.

I doubt that there is no one who has ever used a power saw of any type who has not had a piece of scrap thrown at him/her.

George
You are very close to being correct George, but not exact. There are 5280 feet in a mile, not 5286. The minor error is too small to be concerned about.

As for ejection speed of a piece of wood or carbide tooth:

- IF the carbide tooth simply becomes detached from the blade, it does get ejected at the 172 mph, because that is the speed it was traveling at in use before its bond with the blade failed. However, if the tooth is ejected as a result of collision with a knot or a nail, the speed will be slower as some of its kinetic energy is unavoidably transmitted to whatever it collided with, and only the remainder gets the carbide piece flying off into air space.

- If a workpiece or cut-off piece of a workpiece is ejected, it is going to be at a far lower speed because a lot of the kinetic energy transmitted by the blade to the wood piece is going to be used up accelerating the wood piece from essentially zero fps to whatever velocity the laws of momentum exchange in a collision will drive it to. In addition, some of the blade energy transmitted to the wood piece gets "used up" tearing nice gouges into the wood.

Jim G
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post #35 of 39 Old 01-03-2016, 03:49 PM
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Sometimes a 79 year old memory fails us.

George
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post #36 of 39 Old 01-03-2016, 04:49 PM
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Whatever the Hello the speed was, the TC tooth was going fast enough for me to pick it out of my forehead. The stock was 1/4" Plexiglas.
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post #37 of 39 Old 04-02-2016, 02:51 PM
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I just had to relearn my lesson about leaving scraps on the crosscut sled just moments ago. I left a 3 foot 2X4 on it and before I could think of, well...anything I had that 2X4 flying straight my way. It hit me in the shoulder and I'm ok..It's a little sore, but not as bad as the chunk of finger that made me remember that I have a feather board for a damned good reason..
This could have been much much worse.. Here's one side of the 2X..the other side got a chunk missing as well so it came spinning my way..
Several years ago in a body shop had a chunk of grinding wheel fly back and very nearly ended my sex life..Now that was a tad frightening..It made a believer out of me when it comes to blade guards and handheld high speed grinders..

I figured it's time to change my signature so hold your breath. This is it.
Impressive, huh?

Last edited by allpurpose; 04-02-2016 at 02:59 PM.
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post #38 of 39 Old 04-02-2016, 03:27 PM
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The few kick-backs that I have had, happened so fast that I never knew where the piece landed unless it hit something along the way - like me, sometimes. Several years back I had a kickback and I searched the shop high and low and could not find the piece. When I shut down at night and went to my van, I saw the piece across the driveway in the mini-storage lot. Apparently, it had hit the unit across the way. It traveled about 50 feet and so fast, I had no idea what direction it went.

Tony B



Retired woodworker, amongst other things, Sold full time cruising boat and now full time cruising in RV. Currently in Somerville, Tx
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post #39 of 39 Old 04-02-2016, 10:52 PM
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Sounds like me Tony. Wife and I went out to eat and while sitting at the table I noticed a big dried gash on my arm. I had no idea the flying 2X4 hit my arm. My shoulder hurts, but no gash. Arm? Didn't feel it. It looks a whole lot worse than it feels.

I figured it's time to change my signature so hold your breath. This is it.
Impressive, huh?
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