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Donald Babcock

Planning mods to my grinder

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Ok, first thing is first. I'm trying to figure some basics out before getting to deep into the planning phases.

 

The main thing I need help with is as follows (per the manual):

 

The motor speed is 1725 rpm,arbor size 5/8 inch with a speed of 1750 rpm, and it comes standard with an 8 inch contact/drive wheel, which gives a belt speed of 3600 feet per minute. I'm completly stumped on how to figure out what the belt speed would be with swapping out the 8 inch drive wheel with a standard 4 inch drive wheel. Would the speed be faster or slower with the smaller wheel? And if anybody knows how to figure out what the speed would be that would be great as well.

 

Any help would be appreciated.

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When you calculate the speeds of wheels in relation to size all the pi's and squares and such cancel each other out and all that is left is the ratio of diameters. Therefore if you halve the diameter of the wheel then you also halve the surface speed of that wheel. The same thing applies when you calculate the speed change cause by the relative sizes of the pulley on the motor and the pulley on the grinder. The ratio between the two will give you the answere. That is if the pulley on the motor is 2" and the pulley on the grinder is 6", then the ratio between them is 1:3. Therefore the speed (rpm's) of the driven pulley on the grinder is 1/3 the driving pulley on the motor. I hope this helps, I don't do simple well. I could probably complicate the recipe for mud.

 

Doug Lester

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When you calculate the speeds of wheels in relation to size all the pi's and squares and such cancel each other out and all that is left is the ratio of diameters. Therefore if you halve the diameter of the wheel then you also halve the surface speed of that wheel. The same thing applies when you calculate the speed change cause by the relative sizes of the pulley on the motor and the pulley on the grinder. The ratio between the two will give you the answere. That is if the pulley on the motor is 2" and the pulley on the grinder is 6", then the ratio between them is 1:3. Therefore the speed (rpm's) of the driven pulley on the grinder is 1/3 the driving pulley on the motor. I hope this helps, I don't do simple well. I could probably complicate the recipe for mud.

 

Doug Lester

 

Doug, you just broke my brain! Not really sure what all that means. But let me take a stab at it. The end design will have 4 wheels (for the flat platten attachement) with the motor spindle directly connected to the 4 inch drive wheel. Then there will be a 3.5 inch tracking/tension wheel, and two 2 inch idler wheels in the platen.

 

Now with your explanation above it sounds like the motor and the grinder are not directly connected (thinking like a step pulley setup connecting the two drive shafts). In my case the main change would be the half size drive wheel (going from 8 inches to 4 inches) so this would take the belt speed from 3600 feet per minute to 1800 feet per second. Is that correct or do I need to also factor in the other wheels as well?

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No, don't factor in the other wheels. the only time you have to worry about them is if you are going faster or using very small wheels.

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I don't have any belt grinders, but as a man who has studied lots of arithmetic, I will tell you, Doug Lester is right. You can ignore all the pi's. Just look at the ratio of the wheels. If you're going from an 8" (diameter) drive wheel to a 4" drive wheel, you will cut your belt speed in half.

 

Read this additional text at your own risk. If your wondering where the pi's come from, it's from the following equation.

Speed of Driven Gear = Teeth on driving gear multiplied by RPM of driving gear divided by teeth on driven gear

I know you don't have any gears with teeth, so let's just say inches,

Speed of Driven wheel = circumference of driving wheel multiplied by RPM of driving wheel divided by circumference of driven wheel

= (pi)*D1*(RPM) / (pi)*D2

= D1*(RPM) / D2

where D1 is the diameter of the driving wheel, and D2 is the diameter of the driven wheen, pi = 3.14159...

 

. . . and excuse me for wasting your time if this doesn't apply.

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