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Posted: Thu Mar 12, 2009 5:58 pm
by beeg
At the same speed, would knot a 10" blade at the tip turn slower, than a 9" one?
Posted: Thu Mar 12, 2009 6:42 pm
by JPG
beeg wrote:At the same speed, would knot a 10" blade at the tip turn slower, than a 9" one?
FASTER by PI(3.14159...)
The circumference of the blade is PI times the diameter.
For 10" blade, = 10xPI. Each revolution = 31.4 in. At 3000RPM = 7854 ft/min = 131 FOOT per SECOND! = 192 miles / hour.
For 9" blade, = 9xPI. Each revolution = 28.3 in. At 3000RPM = 7069 ft/min = 118 FOOT per SECOND! = 173 miles / hour.
All these differ by 11%.
The torque required to exert the same force(tooth against piece being cut)will also differ by the same ratio.
Posted: Thu Mar 12, 2009 7:08 pm
by charlese
2manband wrote:Maybe I'm over-simplifying this, but by switching to a smaller blade, aren't you just reducing the tooth velocity and increasing torque? Wouldn't slowing things down with the speed changer have the same effect?
JPG is right again - Have to admit, I didn't think this (9" vs. 10" blade) conundrum through, until I read his posts. Yes the 10" blade will have a 11% faster tooth speed at a given RPM.
With a 9" blade in order to achieve the same tooth speed, you would have to
increase the speed of the machine. With the variable clutches working the way they do - you would actually have less torque on the quill than at the lower speed.
Don't ask me to figure how much torque changes with speed on the Mark V - I think applied torque would vary from speed to speed too much. All I know is maximum spindle torque is at the lower speeds.
Posted: Thu Mar 12, 2009 7:12 pm
by beeg
ONE HUNDRED NINETY TWO MILES PER HOUR!
I NEVER realized that it went that FAST.
Posted: Thu Mar 12, 2009 7:16 pm
by charlese
beeg wrote:
I NEVER realized that it went that FAST.
Gotta remember that speed! That's why it can throw a piece of wood and embed it into a wall. That's also why it'll chop off a finger in short order!
Posted: Thu Mar 12, 2009 7:19 pm
by Gene Howe
Posted: Thu Mar 12, 2009 7:58 pm
by JPG
beeg wrote:ONE HUNDRED NINETY TWO MILES PER HOUR!
I NEVER realized that it went that FAST.
Geez I hope my math is correct!!:D
Posted: Thu Mar 12, 2009 8:00 pm
by 8iowa
According to sawblade manufacturers, a saw that can operate on a 120V 15 amp circuit is "underpowered", and they recommend thin kerf blades. As I see it, the Shopsmith has two distinct advantages over all the others in this class; First, it is very easy to change blades in order to optimize performance, ie: rip, crosscut, plywood, laminate, ect. On most table saws, changing blades is a chore, undertaken only when absolutely necessary. Second, the variable speed feature makes it possible to reduce speed and gain cutting torque, enabling us to cut some pretty tough stock. I remember having to rip the entire 10 foot length of a rain soaked pressure treated 2" x 10". You have to reduce your feed rate accordingly, perhaps making a cut in 30 seconds instead of 15, which is no big deal. I should also mention that the variable speed feature makes it possible to eliminate saw blade burns on some types of sensitive woods.
Mention these features the next time someone trys to "put down" the Shopsmith because of the tilting table.
Posted: Thu Mar 12, 2009 10:04 pm
by reible
Boy that does sound fast... I've heard it was around 100 mph for a normal table saw...
So let me give this a shot.
blade dia * PI * R/M = xxx"/min
10 *3.14*3400 = 106,760"/min
time 60 to convert to in/hour
60*106760=6405600 in/hour
/12 to get to feet /hour
6405600/12=533800 ft/hour
/5280 to get to miles/hour
533800/5280=101.09 miles/hour
Hmmm more or less what I've heard.
now for a 9" blade
9*3.14*3400 =96132"/min
5767920"/hour
480660ft/hr
91.03 miles/hour
Ed
Posted: Thu Mar 12, 2009 11:43 pm
by JPG
Sorry Guys. I apparently miskeyed 2580 instead of 5280 which put me off by about 2x. Ed is right on!:o
