Samller drive wheel for 2x72

P

PaMtnBkr

Joined
Dec 31, 2009
Messages
393
I am currently building a 2x72 grinder and will not have the $$ for a VFD for it, so I will start with a step pulley setup. Seems that everyone likes a slower grinder, rather than a fast one? My thought was that with a 1 HP motor that runs at 1750 RPM, by running a smaller drive pulley, rather than a larger one I typically see on peoples grinders, I can actually have lower belt speed and more torque available? Is my thinking correct? I turn my own wheels so I can make a drive pulley pretty small! I am thinking a 2" drive wheel. Thanks, Don
 
That is correct. Smaller pulley on the motor and larger on the grinder will give you a slower speed. Perhaps someone will chime in with a ratio to determine the actual speed, as I'm curious about this myself.

Motor:
2012-09-24_09-01-51_291_zps9546540c.jpg


Grinder:
2012-09-24_09-02-14_808_zpsa7b765f3.jpg
 
You can just use a ratio of the diameters to determine the new speed, for example if you have a 1" pulley on the motor and a 2" pulley on the belt drive an a 1750 rpm motor you will have a new speed of 1750 x 1/2 or 875 rpm. To put this in perspective the small pulley must turn twice to rotate the big pully once. You can determine the belt speed in feet per minute but using the formula, RPM x drive wheel diameter/12= belt speed in FPM. Two step pullies mounted oposit of each other gives you a slower speed, no change and faster speed.

Torque is an odd animal, a smaller pulley will have less torque, you have less lever arm to pull the belt. You can maintain torque buy using a larger pulley and make the pully on the grinder twice as big, so rather than a 1":2". use a 3":6"
 
I am confused? I ride a mountain bike. When I use my 22 tooth "granny" gear in the front and a 34 tooth on the rear, I go slow, but w/lots of torque compared to using my 32 tooth middle gear in the front and a 34 tooth in the rear? Am I comparing apples to oranges in my thinking? Thanks! Don
 
Large drive wheel in the front where your pedals are, small faster turning wheel in the rear where the wheel is.
 
Yes, mgysgthath, that is correct. Thus the thinking to slow down the grinder, do the opposite. Small drive wheel (where the pedals are) and a larger rear wheel for slower speed but higher torque.
 
I'd think the issue Patrick might have been trying to get at is that the belt is more likely to slip on a smaller gear. 3":6" makes more sense than 1":2" pulley setup.
 
zaph1 said:
I'd think the issue Patrick might have been trying to get at is that the belt is more likely to slip on a smaller gear. 3":6" makes more sense than 1":2" pulley setup.
Click to expand...

My solution was to use 3 step pulleys instead of 2. The setup will produce speeds too slow to be useful and speeds too high to be comfortable using. I have no plans to go to variable speed. My 2c
 
And to answer the OP's original question......
Yes, a smaller drive wheel will lower the belt speed and increase the delivered torque.
 
Thank you all! I am turning my drive wheel and my idler wheels tonite after work! Can't wait to get this thing done! I have been taking my time to make sure it's done once, done right! Thanks again to all of you for info! Don
 
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