Your web site indicates you have a strong physics background. Would you mind putting some calculations together for us for the major saw horsepower ratings? I think we mainly know horsepower to start with, not torque. Can you figure out some ballpark velocities and force numbers for 1 hp, 1 1/2 hp, 3 hp and 5 hp saws?
(if you have time, of course. I'm just curious...)
-m
Something my Dad taught me and I try to live by ;- 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
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.
G'day Greg, 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
I had a piece of 3/4" ply 14" X 14" kick back. The saw flung it so fast I never saw it. It was flung spinning like a Frisbee, hitting me on the left hip, and deflecting off at about right angles. It flew 10 ft or so and smashed into one of those transparent plastic bins, which totally exploded. I wasn't hurt at all, only because the spin on the Frisbee was advantageous.
-jbb
Of course, that trip into the ER and the 4stitches probably ran up a $1000+ ER bill, hope you had medical insurance of some kind
John
"Mike W." wrote in news:RwAaf.185144$lI5.26150 @tornado.ohiordc.rr.com:
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Once. Failed to push the piece far enough past the back of the saw blade, and it vibrated forward and caught the back end ... wham.
It didn't hurt me because I was standing left of the blade. I always use the blade guard and splitter where possible, and for narrower cuts I use fingerboards. The bolts for my Jet splitter/guard are replaced with hand- turn knobs to make it fast to remove and install. For crosscuts I prefer a sled.
It sure was enough to put the fear of God in me, though. And it seriously messed up a beautiful little bookmatched flame cherry panel I'd been working on.
"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.
Some years ago I was cutting a 2x2 square of fiberboard on the tablesaw. For some reason I did not hold the material tight against the fence and it slightly rotated, kicked back, and hit me in the thigh. I suffered a black-and-blue mark and was lucky the hit was not in the gonads.
Not a table saw story, but about 25 years ago, a friend was killed in a saw mill kickback accident. Cecil was a preacher, farmer, mechanic, and all around jack-of-all-trades. I'm not certain how it happened but the piece hit him in the head. He had a closed casket funeral. RIP Cecil.
Gary
What a way to start the day... Sorry for the loss of your friend, he sounds like a real Renaissance Man - in dungarees.
Ever seen a 60" mill saw operated with no guards, and almost no safety equipment? Or trim/grading operators working with a 22" blade 12" from their left arm... scary stuff!
Greg G.
When I first started woodworking I had a pretty nasty kickback. I was trying to rip a big piece of plywood (no infeed or outfeed table) and while pushing it through allowed it to twist just enough to catch the back of the blade. Piece lifted up and was thrown into my gut, hurt like hell, monster bruise. Looking at the piece you could see where the teeth had grabbed it and thrown it back. These days I have two of the anti kickback wheels that attach to the fence and a griptite to keep stock firmly against the fence, I also use a tru-grip and circular saw for my big panel cuts these days.
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