Motorized Grain Mill Ratios

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klickcue · #1 Post by **klickcue** » Thu Mar 01, 2012 10:39 pm

Here is some help in pulley ratios for a grain mill.

Since a grain mill runs at a fairly low speed, cast zinc pulleys should be fine for the application. Cast zinc is fairly cheap also.

Assume that you find a 1/2 electric motor that works and has an RPM of 1750 on the nameplate and is 110 volts.

Things that your need to know before buying pulleys. What is the output shaft size on the motor? What is the input shaft size on the mill? Below is going to be generalize because of the unknown elements of the motor and mill.

So, you want your mill to operate at 175 RPMs at the input shaft and you have a 1750 RPM motor. So 1750 / 175 = 10:1. You need a 1" pulley on the motor and a 10 " pulley on the mill.

Let's take it step further, you want the mill to run at 200 RPMs. 1750 / 200 = 8.75:1. This would be a 1" pulley on the motor and an 8.75" pulley on the mill. It may be hard to find an 8.75 pulley since 9" is more common. What can you do? You buy a 4L belt pulley but use a 3L belt on the drive system . A 3L belt is narrower than a 4L belt so it rides farther down in the pulley and gives the little bit of gear reduction.

You may find that the bore of the pulley that you have chosen is larger than you need. You can buy both step up and step down reducers. These are fairly expensive so it is better to find pulleys to you want to operate at. Let us say that 300 RPMs is maximum for a mill.

Another thing that can be done of to buy a bronze bushing with the ID and OD for your purpose. You can glue the bushing into the pulley or onto the shaft with epoxy. You may get a little more run out on the shaft, but at the low RPM, it may not be even noticed.

Try Grainger or McMaster for all you options:
http://www.grainger.com/Grainger/wwg/start.shtml
http://www.mcmaster.com/#

You may be able to get away with a 1/3 HP motor but given that you might have a rock in the grain, 1/2 HP is safer.

A quick calculator that is on the web:
http://www.culvermotor.com/Engineering- ... lator.html There are other available.