Is My Math Correct for the pulley speed?

Janderso

Janderso

Jeff Anderson
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Mar 26, 2018
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Example:
3,450 RPM Motor with a 2" pulley.
2" pulley is driving a 6" pulley
6" pulley is driving a 2" pulley
2" pulley is driving a 6" pulley.
The last driven shaft is rotating at 383 RPM.
Do I have it right?
Thanks,
Jeff
 
just to clarify: motor (2") > countershaft 1 (6") > countershaft 2 (2") > load (6")

that would give you a 3:1 reduction then a 1:3 increase then a 3:1 reduction

so
countershaft 1 would be running at 1/3 of motor speed = 1150rpm
countershaft 2 would be running at 3x countershaft 2 speed = 3450rpm
load would be running at 1/3 of countershaft 2 speed = 1150rpm

basically your 2 countershafts cancel each other out, so you have a 3:1 speed reduction from motor to load (if I understood your post correctly)
 
Janderso said:
Example:
3,450 RPM Motor with a 2" pulley.
2" pulley is driving a 6" pulley
6" pulley is driving a 2" pulley
2" pulley is driving a 6" pulley.
The last driven shaft is rotating at 383 RPM.
Do I have it right?
Thanks,
Jeff
Click to expand...
I think you reversed something, The last two cancel each other out. If you are wanting the middle 6", driving the 2", as both being on the same shaft, as in both rotating at the same speed, then I get the same 383 RPM's
 
Superburban said:
I think you reversed something, The last two cancel each other out. If you are wanting the middle 6", driving the 2", as both being on the same shaft, as in both rotating at the same speed, then I get the same 383 RPM's
Click to expand...

Yes, you did a better job!
The example is a real scenario if I choose to use this motor.
I need to reduce the speed to build a lapping machine for carbide scraper blades.
I'm just checking the math. Motor speed times pulley = 6,900 divided by 6" pulley = 1,150 rpm
1,150 times 2 = 2,300 divided by driven pulley (6) = 383

If I can find a 1,750 RPM motor, I could go directly from the 6" pulley to drive my lapping plate at 583 rpm but I think that's too fast??
In other words, 1750 rpm motor with a 2" pulley driving a 6" lapping plate = 583.

Thank you
 
ah, so the 6" and 2" would both be on the same countershaft. No reason that wouldn't work.

Easier way to work out speed reductions. Work out the pulley diameter ratio for each step (2" to 6" = 6/2 = 3:1 reduction), then multiply all the steps. Then you just have to divide the motor speed by the total reduction ratio.
 
Jeff, most of us look for about 200-300+ rpm for sharpening carbide scraper blades. Look at the Glendo specs for what speed theirs is. Remember also that cutting speed is related to where the work will be on the wheel. Closer to the hub, slower SFPM, farther from the hub, faster SFPM. Glendo wheels are smaller than the 150mm Chinese diamond wheels, if that is what you are planning to use.
 
Thanks guys,
I have a motor I can use, I think it works. It was a freebie
 
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