Sam's Motorized Grain Mill

Many of us with a passion for brewing beer at home seem to follow a progression in the hobby. We gobble up every bit of information we can, learn new things, and challenge ourselves by experimenting with new techniques and equipment. If you've recently made the move to all-grain brewing (or are contemplating it), one of the things to consider is the purchase of a grain mill. Of course, you can have your grain crushed by the homebrew shop but you'll quickly learn that owning a mill provides some great benefits. A couple of the most important benefits are the flexibility you'll have when planning a brew-day and the ability to produce a consistent crush that is matched to your system and produces a predictable efficiency.

What's that you say? You already have a mill and want to know the next step in the progression of your homebrewing obsession, er, hobby? Well, duh… it's adding a motor, of course!

I've documented the building of my motorized mill below… I'm not an electrician and this isn't a how-to (don't blame me if you electrocute yourself). However, it should give you some ideas if you decide to proceed with motorizing your own mill.


  • (1x) cabinet (garage sale find)
  • (1x) small length of 2×4 lumber (final length is about 9 inches)
  • (1x) grain mill : Barley Crusher MaltMill [website]
  • (1x) gear motor : 105.7 RPM 115 VAC GE GEARMOTOR [website]

  • motor to mill coupler:
    • (1x) Flexible Spider Shaft Coupling Hub 3/8" Bore, 1-5/64" OD (for the Barley Crusher shaft : McMaster Part #6408K113) [website]
    • (1x) Flexible Spider Shaft Coupling Hub 1/2" Bore, 1-5/64" OD (for the gear motor shaft : McMaster Part #6408K711) [website]
    • (1x) Buna-N Spider for 1-5/64" Outside Diameter Flexible Spider Shaft Coupling Hub (McMaster Part #6408K84) [website]

  • (2x) angle brackets (4-1/2” by 4-1/2” by 1-1/2”)
  • (1x) old computer power supply with cord (this will be dismantled so it doesn't need to be working)
  • (1x) single-pole-double-throw (SPDT) ON-OFF-ON switch [website]
  • (1x) blank 2-gang wallplate cover (for mounting switch)
  • (7x) insulated female disconnects for 16-14 AWG wire [website]
  • rubber grommets (for passing wire through cabinet and/or power supply case)
  • heat shrink tubing

  • hardware to mount 2×4 to top of cabinet:
    • (4x) 5/16" x 2-1/2" oval-head phillips machine screws (length depends on thickness of cabinet)
    • (4x) 5/16" finish washers
    • (4x) 5/16" x 1-1/4" fender washers
    • (4x) 5/16" nylon insert lock nuts

  • hardware to mount mill:
    • (2x) 1/4" hex bolts (length depends on thickness of cabinet)
    • (2x) 1/4" cut washers

  • hardware to mount angle brackets
    • (4x) 1/4" hex bolts (length depends on thickness of cabinet)
    • (4x) 1/4"cut washers
    • (4x) 1/4" x 1-3/8" fender washers
    • (4x) 1/4"lock washers
    • (4x) 1/4"hex nuts

  • hardware to mount motor to angle brackets
    • (4x) 1/4"lock washers
    • (4x) 1/4"hex jam nuts

  • hardware to mount wallplate cover
    • (4x) small (#4?) oval head sheet metal screws

The Build

I had been following some forum threads that discussed motorizing mills for a while but never really got motivated until I saw my friend Josh's setup. As soon as he flipped his mill on, I moved this project to the top of my list. It was awesome. The motor was quiet and ran nice and slow (unlike the cordless drill that I had been using with my mill). His mill was sitting on a butcher block table that wouldn't tip over if bumped (unlike my bucket which had tipped over on more than one occasion while full).

That weekend I found a sturdy wooden cabinet at a garage sale… perfect. The doors would keep the grain dust contained and an adjustable shelf would allow me to position a bucket right underneath the mill.

The first step was to figure out where things would go. I laid everything on top of the cabinet and took some measurements.

I wanted to make sure that the mill's hopper didn't protrude past the sides of the cabinet when coupled to the motor and that I could position a bucket directly below the outlet of the mill; also keeping in mind a place for the switch and where to mount the motor's run capacitor.

I also wasn't quite sure how to line up the shaft of the motor. I had found some angle brackets to mount the motor and was trying to stack some pieces of plywood under the mill when I came across a piece of scrap 2×4 in my garage; turns out it was just the right thickness. I laid out my lines, cut with a jig saw and drilled for the bolts.

To mount the motor, I used a couple of heavy-duty angle brackets. The brackets came with some off-centered holes for small screws or nails. I drilled new holes to accommodate both the motor's mounting bolts and the bolts used to attach the bracket to the cabinet.

Connecting the motor to the mill with a spider (or jaw) coupling has some advantages. It allows a small amount of play so you don't have to line them up perfectly and the rubber "spider" dampens some of the vibrations to keep things quiet. Driving the mill shaft directly like this is also safer; i.e., there are no belts or pulleys that could accidently grab hold of a piece of clothing, finger, hair, etc.

One of the things I was having a hard time with was how to wire the motor up with a reversing switch. A few of the examples that I found online were wired with DPDT switches but the wiring diagrams just didn't make sense to me. Finally, I came across a post by the BN's codewritinfool that made perfect sense (thanks Code!).

From the motor's wiring diagram we can see that when power is supplied to the blue wire, the motor will rotate in a clockwise fashion (which is the direction the BarleyCrusher needs to turn). To reverse the motor, the hot wire needs to be switched from the blue to the red wire. You can accomplish this with either an SPDT switch or one side of a DPDT switch.

When I bought my switch I paid a little extra to get a lighted rocker. (When the green side is pressed down, the red side is illuminated and vice-versa; not the way I intended but oh well… I guess it makes sense if you're in a dark room.) You'll notice this SPDT switch seems to have an extra center terminal. This extra terminal is just used to light the switch. You can see where I've jumpered the black (hot) wire to it in some of the pictures. To mount the switch, I used a rotary tool with a cut-off wheel to make an opening in a blank wall plate. (I love my cut-off wheels… same ones I used in my keg-to-mash-tun conversion.)


For the physical wiring, I took the guts out of an old PC power-supply and reused the wires. I mounted empty power-supply case towards the back of the cabinet and used a hot-glue gun to attach the capacitor. Female disconnects (spade connectors) were used to connect the switch and capacitor. Since the motor came with a Molex connector already attached, I was able to just reuse one from the power-supply.


Colored electrical tape made it easy to keep track of the wires and a rubber grommet added a nice finishing touch. The Molex connector will make it easy to switch out the motor if it ever goes bad.


Here's the view from underneath. Some of the bolts were longer than I wanted so I cut them to size with my dremel and cutting wheel.

Time to blow through some grain!

Some links that inspired me…

BeerPal's forum threads:

BCMaui's motorized grain mill:

Other motorized-mill links:

To see some of my other builds, visit my page on the ALEien's website:
Sam is a Senior IT Consultant and partner at Fox Wyndrum Associates. He lives in Bridgewater, NJ with his wife Sarah, two boys Jacob & Ronan, and chocolate lab Cisco. When not expounding on the importance of fermentation temps at the ALEiens Homebrew Club, he can be found at home roughhousing with his kids and loving every minute of it!
Jeff Louella on 03/25/11 10:36 am writes
Great post. You have inspired me to start looking for a cabinet at yard sales.
BBrocker on 10/25/11 04:46 pm writes
Thanks for the tips and the links!.. I ordered the same motor and couplings.
Kevin on 11/07/11 06:02 am writes
I just built this yesterday, and love the great detail in your instructions. Thanks!

I wondered if you get good speed on the motor, though? I had used my drill on the barley crusher before and would crush 30 pounds in about 5 minutes. This appears much slower.
Larry B on 11/20/11 02:18 pm writes
I really don't see the pupose of the capacitor. The connectors are U shaped and the energy will byepass the capacitor. Two reds at one wires at one terminal and two blue wires at the other terminal.

Can anybody help with this question???
Sam on 12/04/11 06:10 pm writes
Kevin, slow is good! When using my drill at high speed, the husks on the grain would end up torn and shredded. I've found that the slower speed provides a much better crush. It only ends up being a couple minutes longer and I don't stand there and watch it... I just dump the grain in, switch it on and go do something else for 10 minutes.

Larry, the capacitor comes with the motor and is wired according the the manufacturer's diagram (check the link above labeled "motor's wiring diagram"). I'm no EE but the switch sends power to one side of the capacitor or the other... this controls the direction of the motor's rotation.
Nick W on 12/14/11 12:52 pm writes
@Larry B: The capacitor is not bypassed. The motor is a capacitor-start, capacitor-run motor, aka Permanent-split capacitor motor. The capacitor provides more starting torque, and it also adjusts the power factor of the running motor so more energy goes into making the motor spin rather store energy. You can read the wikipedia page here: It's not the easiest concept to grasp, but without the cap, the motor could turn in either direction on start and wouldn't have enough power to start under load.
Tony Legge on 02/04/12 05:43 am writes
You inspired me to motorize my mill. While mine isn't contained like yours is, I went with a folding table set up where the side that had legs folded under the table and the other end was supported by the receiving bucket.
Other than that, mine is very similar.
Thanks for posting your build.

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