Step by Step Motorizing a Grain Mill

Thank you to HBF Reader Aaron N for this step by step how to!  Aaron is a long time reader and a serial tipster!

This is an advanced project that requires a good bit of materials, tools, knowledge and skill.

Motorizing Your Mill, Purpose Built Solutions

Important: These are the steps that Aaron took to put his build together.  This post does not constitute an endorsement of this process.  It is provided for informational and entertainment purposes only.  Your situation and equipment may by different.  Make sure the components you use are compatible and rated for your intended application.  Contact manufacturer with questions about suitability or a specific application.  Always read and follow manufacturer directions.  Always exercise caution around electricity, moving motors and moving mills.  If you have questions about wiring, contact a licensed electrician.  We recommend a purpose built solution for motorizing your mill.

Related Resources:

Note: A critical part of this build is incomplete.  This is a safety issue.  Aaron mentions in step 19 that he needs to add a guard and asks for ideas.  Leave a comment on this post if you have an idea or email us and we’ll forward it on.   As mentioned previously we recommend a purpose built solution for motorizing your mill.

How To: Step by Step Motorizing a Grain Mill

Step by step instructions on how to motorize a grain mill for milling barley.
Part of the joy I have in being a homebrewer can also be described as a sickness. Once the buying of equipment and accessories begins one becomes infected and may find it difficult to stop buying and making in the name of supporting the hobby. Writing this in the time of COVID, the homebrewing sickness may be even more appealing – it can help to satisfy the thirst for delicious brew without having to leave home and it also satiates a desire to make and to build at a moment when many of us have more time on our hands. The motorization of a grain mill for me was a project that satisfied my desire to get even deeper into the all grain aspect of brewing, remove the reliance on my local homebrew shop’s mill (which incidentally closed not long after I finished this project), and allow me to engineer something that would help support my hobby for hopefully a long time.


  • Grain Mil
  • Drive Sheave
  • Motor Sheave
  • Bore Collar (depending on diameter of the motor and/or mill shaft)
  • Electric Motor
  • Belt
  • Electric Switch
  • Single Gang Electrical Box and face plate
  • 12/3 Romex
  • (2) Cord Clamp
  • MDF Board
  • 2 x 4 board
  • 1 x 2 board
  • Wood screws
  • (2) 22-inch Drawer slides (rated to support weight of motor and mill mounted on the MDF platform)
  • (2) Large worm gear clamps
  • Flat corner braces
  • 2 x 4 joist hanger

Tools Needed:

  • Saw
  • Drill
  • Drill bits
  • Screw Gun/Driver
  • Tape measure
  • Metal file
  • Wire strippers
  • Multimeter
  • Rubber mallet


  1. Begin to source the materials starting with the grain mill. I chose the Cereal Killer mill from Adventures in Homebrewing after reading the reviews as it was highly rated and on the lower end of the cost spectrum. The next piece to consider would be the motor. Many electric motors could be configured to run the mill and there are even some that are manufactured expressly for running grain mills. I chose an old Maytag washing machine motor after finding it locally on Craigslist for $25. It is at least five decades old and still running strong. If you choose to use a motor not designed expressly for powering your mill be sure that it will be powerful enough to do so.
  2. Once the mill and motor are in hand it is time to crunch some numbers. The mill will have a recommended operating speed in RPMs. The Cereal Killer mill specifications stated that it should be run at 300 RPM, however, I decided on shooting for 200 as it was in line with most recommendations I found online for milling brewing grain. Next, determine the RPMs of the motor (mine was listed on the manufacturer’s tag on the motor). My Maytag motor runs at 1725 RPMs, so I had to find a way to slow that down. I found a pulley calculator online like this one and played with the numbers until it was clear what size pulleys would work to lower the RPMs to the desired rate. I found that a 12-inch pulley (aka sheave) for the mill and a 1.5-inch pulley for the motor would slow the RPMs to 216 RPMs.
  3. Knowing the outer diameter of sheaves, I set about to find ones that had the same inner diameter to match the motor and mill. The mill shaft was 10mm. I ended up finding a 12-inch sheave on eBay with a ½ inch bore for $44. In order to fit the ½ bore on a 10mm (.394 inches) I found a 3/8 to ½ inch collar and filed the mill shaft down ~.02 inches. I found a 1 ½ inch sheave with a ½ inch bore on Grainger for the motor for $10. Make sure that both sheaves support the same size belt. Mine were for ½ inch belts which I believe is common.
  4. For the belt, I found an adjustable version called a link belt that would give me the flexibility for the spacing I needed between the motor and the mill. There are fixed length belts, like the kind you would find under the hood of car, that would work, but then the distance between the motor and mill will be fixed as well. Harbor Freight has a highly rated “vibration free” link belt ½ inches wide that I have found to work well. Over time it has stretched a bit and all I had to do was take out one link.
  5. Determine where the final assembly will be located, especially if employing the drawer slide option or other static location. It would be feasible to mount both motor and mill to a platform that could be transported like on a cart. What follows will be for mounting to a sliding platform in a fixed location as this is what I ended up doing in my basement brewery. I had a small space between my chest freezer and my brewing equipment shelves that was just wide enough for a sliding platform with the mill and motor.
  6. My platform is 24.5 inches long by 12.5 inches wide which will fit the motor in the back, positioned so that the drive shaft is parallel with the short side of the board. The sheave is located 9.5 inches from the long side of the board and the center of the drive shaft is 5 inches from the short side of the board leaving 19.5 inches to the front of the board. I lined up the grain mill (without attaching the sheave yet) and marked the location to mount it based on how the mill drive shaft lined up with the motor drive shaft. They should be parallel aligned to allow for the correct sheave and belt arrangement. My mill is 5 inches from the long side of the board and the drive shaft is 12 inches from the motor drive shaft measured from the center of each shaft. With the positions roughly marked, I determined where the holes need to be cut/drilled to secure the motor and mill and marked them but did not drill them yet. The other measurements detailed later may impact placement a bit, so it is best to wait until all positions are known before drilling/cutting. For the motor I used two 4-inch worm gear clamps that wrap around the two mounting points on the motor and are fed through holes in the platform that I drilled with a ½ inch bit. I marked those positions but did not drill them yet. The mill came with mounting hardware which consisted of two machine bolts. I marked the location of the holes on the platform for the mounting holes as well as the for the mouth of the mill.
  7. With the mounting positions known I then determined where the slat would need to be to allow the mill’s drive sheave to be attached. I had to consider not just the overall size of the sheave, but also the belt travel from the mill to the motor. To give proper clearance to the sheaves and belt my slat measured 1-5/8 inches wide by 17 inches long with 6.5 inches measured from the center of the mill shaft to the near side of the board (away from the motor) and 10.5 inches to the far side (toward the motor). One factor that I didn’t consider until mounting it all was the outer width and thickness of the mill sheave’s throughbore, what I learned later is called the “stick-out”. It is the center part of the sheave where the drive shaft will be mounted which does indeed stick out more than the main part of the sheave wheel. I marked a small depression on the platform to account for this which I later drilled out.
  8. The only other component that needs mounted to the platform is the electrical box for the switch. This can really be placed anywhere that is out of the way of the operation of the drive belt and is easy to access when the mill is in operation. You don’t want to position it where there is any danger of getting fingers, clothes, or anything else caught in the sheaves or belt while in operation so somewhere on the opposite side of the platform from the drive belt is sensible. This can be mounted after the motor and mill holes are in place.
  9. With the platform accounted for I measured and cut the supporting wood pieces that would be used to hold the platform. I used a combination of 2 x 4 and 1 x 2 boards, the former for the support structure and the latter for mounting the drawer slides to the platform. My structure is tied into existing wood shelving in my basement as well as the wall studs. That left the following as necessary supports: one vertical support leg, a horizontal support that would hold one part of the drawer slide, a back support to tie into the wall studs, and a cross brace that goes between the shelving upright and the vertical support leg. In order to get measurements for these pieces I determined the desired height of the mill to be 28 inches and cut the pieces accordingly. This resulted in the vertical support leg being 27.25 inches long, the horizonal drawer support being 23 inches, the cross support being 15.75 inches, and the back support being 24 inches long (my wall studs are 24 inches apart). The 1 x 2 drawer supports measured 22 inches long.
  10. With all the support structure measured and cut it can be assembled. The back support was screwed into the wall studs with the top of the 2 x 4 measuring 26.5 inches off the ground. I used a joist hanger to tie the horizontal drawer support 2 x 4 into the back support and flat corner brace to attach the vertical leg support to the horizontal drawer support 2 x 4. I used another flat corner brace to attach the horizontal cross support to the wood shelving upright and the vertical leg support with the top of the horizontal cross support measuring 18 inches from the ground.
  11. The 1 x 2 drawer supports were attached to the platform with the short side of the 1 x 2 edge being flush with the front end of the platform where the mill is located. The long sides were flush with either side of the platform and attached. Following the instructions provided with the drawer slides I mounted the inner slide (male) on the 1 x 2 drawer support and the outer (female) on the horizontal supports of the structure. To finish the platform support I added a 2 x 4 piece to the face to act as a handle that mounted to the front of the platform, screwed into the MDF and the 1 x 2 drawer supports. This measured 15.25 inches long.
  12. Not knowing a lot about the motor and having only hobby experience with electrical (read as a disclaimer: I am not an electrician and you should consult one if you are not comfortable taking the risks I did with the wiring), I hoped I could reverse the polarity to throw the mill in reverse if needed to dislodge stuck elements in the mill so I picked up a double pole, double throw switch. When I powered it on, despite checking the wiring and re-wiring in different configurations, I found that my motor can only go one way. I haven’t had a stuck mill in the two plus years I’ve been operating it, so I now know this was an unnecessary consideration. Ergo, I would recommend using a single pole/throw (SPST) switch. The wiring for a SPST switch will take the black wire from the motor on one post and continue that black wire out on the other post. The white and green wires from the motor will bypass the switch to the out cord going to the power outlet side. The motor I got had a long cord which I cut in order to tie the switch in so you may need extra 12/3 Romex or similar wire to support. Just be sure that the wire and the switch are rated to accept the voltage and amperage specifications of the motor.
  13. The electrical box I used was a single gang box. I used a blank face plate and drilled a hole large enough for the switch to go through. I mounted the switch to the face plate after determining the wiring and punched out two holes in the box for the input of the power cord and the output. I then used cord clamps to secure the cords and ensure that any pulling of the cord would not disrupt the wiring in the box.
  14. Moving back to the motor and mill I needed to secure the sheaves to their drive shafts. Having done the hard work of fitting the mill drive sheave earlier, this step was straightforward and involved placing the sheaves on the drive shafts and tightening the keyhole screws on each sheave. A rubber mallet came in handy to fit the sheave on, especially on the mill shaft as it was a tight fit.
  15. The mounting of the mill and motor were next. I secured the motor using the 4-inch worm gear clamps, keeping it loose to allow for the addition of the belt in the next step. The mill was secured using the two bolts provided with the mill and was fastened tightly.
  16. Next, I put the link belt on. The handy feature of this belt being that the links can be added or removed made this part simple. I started out with an estimated length of the belt and positioned it around the drive sheaves, taking out links until it was the right length. Once the belt was in position, I tightened the motor’s clamps, ensuring that it would not move at all.
  17. When in operation, the mill will put out a lot of grain dust. In order to capture some of that as well as provide an avenue for the crushed grain to travel I attached a makeshift chute to the bottom of the platform directly under the mill’s mouth. Having a 55-pound bag of malt ready to be crushed, I filled my grain container with grain and used part of the empty bag as the chute. I cut a section out about 12 inches long and stapled it to the bottom of the chute.
  18. Before operating the mill, I set the mill gap. A set of feeler gauges is helpful in this endeavor but doing it by sight. You want the grain to be crushed with the husk intact. I have mine set to .021 inches. Without a feeler gauge you can experiment by passing grain through, inspecting it, and adjusting as necessary. Start with the closest the mill can be gapped without the rollers from touching one another and widen the gap as necessary. You don’t want to completely pulverize the grain as some believe that can lead to astringency in the finished beer.
  19. The last step is one that I have yet to do myself: put on guard over the drive sheaves. When in operation, the potential for getting fingers, long hair, clothes, etc. caught in the sheaves or between the sheave and the belt it high. If you can mitigate that risk at all I would advise it. Mine is in a corner of my basement where I can maneuver around it without being on the operating side of the apparatus. However, I still leave mine unplugged when not in operation and leave the switch off, too. I never reach around or over the spinning sheaves and keep care to not let anyone else around it while operating. If I had a sheet metal bender, I would get some HVAC sheet metal and construct a small guard over the mill sheave and belt. If anyone has any other ideas for a guard, please let me know!

Motorizing Your Mill, Purpose Built Solutions

We recommend a purpose built solution for motorizing your mill.


These are the steps that Aaron took to put his build together.  This post does not constitute an endorsement of this process.  It is provided for informational and entertainment purposes only.  Your situation and equipment may by different.  Make sure the components you use are compatible and rated for your intended application.  Contact manufacturer with questions about suitability or a specific application.  Always read and follow manufacturer directions.  Always exercise caution around electricity, moving motors and moving mills.  If you have questions about wiring, contact a licensed electrician.  We recommend a purpose built solution for motorizing your mill.

Homebrew Reviews: Grain Mills

Homebrew Finds makes no representations as to accuracy, completeness, currentness, suitability, or validity of any information in this article and will not be liable for any errors, or omissions in this information or any losses, injuries, or damages arising from its display or use. All information is provided on an as-is basis. To use Homebrew Finds you must be 21 years or older. toppost:motorizemill tag:tpr

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