Motorize Your Mill

Crushing grain immediately prior to mashing is one of the hallmarks of homebrewing at its finest and is well documented in numerous articles. I have used a drill-powered mill for years, but recently undertook the challenge of motorizing it.

In milling, the roller speed and gap between the rollers are of utmost importance. Too slow and it takes a very long time to mill the grain. Too fast and the grains will not be crushed for optimum efficiency in the mash.

By doing some simple calculations, we can determine the correct pulley size based on the motor’s RPM. Electric motors are built with standard speed ratings. Most are either 1725 or 3450 RPM. Unless you are using a jackshaft arrangement with four pulleys, the 3450 RPM motor is seriously too fast

Another consideration is motor horsepower. If the horsepower is too small it will have problems running the mill, but the cost goes up considerably with the more horsepower you have, so there is no need to overdo it either.

For this project I decided to use a ½ horsepower motor that runs at 1200 RPM and it is under slung on table, thus allowing additional workspace for scale etc. This motor is also TEFC (Totally Enclosed Fan Cooled), meaning grain dust cannot get into the motor and possibly ignite. If you are like many homebrewers and enjoy fabricating your gear, no worries; motors can be salvaged from many sources such as washers, garage door openers and HVAC blowers to name a few. Many times they can be had for free, but may require some work to remove from original mounts. If you don’t have an old, out of commission electronic to take a motor from, they can often be sourced online from sites offering free classifieds.

Under mounting also keeps belts and pulleys safely hidden, which is important, as I really want to keep all of my fingers.

There are a few things that will not be covered in this article … namely building a cabinet, frame or another structure supporting the motor and mill as the options are endless. I will focus on mounting the motor, the pulleys (sheaves), belt sizing and speed requirements.

Before we get started; one word of safety. If you are not absolutely comfortable working with electrical connections, find a friend that is comfortable working with electricity or contact an electrician. Perhaps you are a member of a local brewclub and can ask for members’ assistance. Our club ( sees this type of posting on our website regularly and many members are more than glad to help … possibly in exchange for some homebrews.

Parts and materials
Pulleys – McMaster-Carr
1 ½- inch pulley
9-inch pulley
Angle steel and rod