Post in 'The Gear' started by BS-N, Dec 5, 2005.
http://www.designnews.com/article/CA6286281.html?text=the case of the deviant drill
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Ouch. That had to hurt.
In the same general area, does anybody know what the speed of the chain is at the tip of an average chain saw?
I know that the clutch speed as stated in the above story is usually between 10,000 to 14,000 or so R.P.M.
I also know that speed is distance over time and that the theory behind gears and things is that the larger the diameter, the longer time it takes a given point on the outside of the circumference to complete a revolution, therefore slower speed.
I picture a chain saw bar as just an elongated circle, therefore the chain circling around the bar will be travelling at a slower speed than at the clutch?
Yeah, I know, I need to get a life and quit wondering so much about life's little mysteries.....
Actually, I think the farther out from the center of the shaft, the faster it goes. Circumference = pi x diameter, if you have a 1" diameter sprocket, and it is rotating at 1rpm, the chain speed would be ~3.14 inches/minute, whereas if you have a 3" diameter sprocket, and it is also rotating at 1rpm, the chain speed would be ~9.42 inches/minute. So take your circumference (just of the sprocket) and multiply by rpm to get you speed. I am a chemist, not a mathematician, so excuse me if I am wrong, but I think this will give you a close estimate of chain speed.
Way back when I dinked around with the numbers and came up with something like 5,000 feet per minute chain speed with "Big Yaller" running full bore.
Good read. I can't imagine the pain involved. My father took some metal in his eye (long story) and he kept going back to the eye doctor for 2 1/2 years and is still legally blind in that eye.
Chain speed will be the same at any point on the bar or at the pitch line of the engine sprocket... Unless you have a rubber chain LOL ...
I believe Hosspuller is right. Clutch speed equals chain speed.
Try that on for size. There are tons of other relationships too, I believe this is a correct one.
You can always relate the total length of the chain to the circumference of the clutch gear, but this way is, simpler.
Calculation makes sense to me, in that it takes into account that the sprocket must spin more than once to move the chain in it's entirety. That's also why I figured that chain speed had to be less than sprocket or clutch speed.
So what's that work out to in R.P.M. ?
well truthfully, I just pulled those numbers out of thin air. You'd have to take a look at your own saw, because I don't even know if those are ballpark. Just random numbers.
but to go from miles per hour -> rotations per minute you'd have to know the length of the chain
assuming chain length is 36"
Take the number of inches the chain moves her minute (50,000 in/min)
50,000 in/min x 1 revolution of the chain/36 inches = 1,388 rpm
*Disclaimer- I make all these numbers and formulas up, don't go betting your Mercedes on my chain speeds.
Corie's got it right. The ft/minute will be same as the ft/minute of the sproket. The RPM is much different since basically the sprocket is driving a much larger gear (the bar circumfrence, including the sproket)
Right. That's essentially the argument I was proposing when I initially asked the question. Because the chain and bar is esentially a big sprocket, it can't possibly have the same RPM as the clutch. Corie's f.p.m./r.p.m. calculation makes sense, at least to me.
Makes sense down to the point where the 50,000 ipm is multiplied by 1mi/5280 in to get the 9 miles per minute figure. One mile is 5280 feet, or 63,360 inches so the figure should be 50,000 ipm * 1 mile / 63360 in = .8 miles per minute or ~48 MPH which is a little more in the realm of what I would expect. I kind of shuddered at the fact that my chain may go trans-sonic if I were to put a few more revs into the engine!
It's OK...happens to the best of us sometimes!
haha, you got me. I knew something wasn't right in there, but between studying for finals I didn't have a chance to really look it over.
Also, like I said, I just pulled those numbers for teeth per inch and teeth on the sprocket out of thin air. I really have no idea what they should actually be.
Just for the heck of it, I measured the chain on my Husky 350 (i didn't do all the tooth - pitch conversions) but 1 revolution of the clutch bell moves the chain 4-9/16" along the bar, so that gives it a surface speed of just a shade over 56 MPH @ the published 13,000 RPM no-load speed...assuming there is no slipage of the clutch which there will be some.
I know lawnmower blade tip speed is regulated to some figure (19,000 feet per minute comes to mind, but don't quote me!) I don't know if there are similar regulations for chain saws or not.
Too bad about the guy in the original post, but if anyone ever watches the show "Mythbusters", Adam tried something similar in the "Jailbreak" episode. He taped a drill bit to a vacuum cleaner motor (if memory serves). It went catastrophic about 1 second after he turned on the power. Luckily no one was hurt there.
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