Cheap DIY Option for a Motorized Grain Mill

If there is one thing that can be said about homebrewers, it is that we are a DIY-type crowd. In fact, the very act of homebrewing is DIY, in that you are brewing it yourself, instead of buying in from the store. It is no wonder, therefore, that homebrewers tend to fabricate or re-purpose items to perform a variety of the tasks involved in homebrewing. Whether a homebuilt stir plate made from a computer fan and hard drive batteries (I’ve made two), re-purposing kegs as brew kettles, or converting freezers into fermentation chambers, there is no limit to the ingenuity of homebrewers to accomplish a task or simplify a process. Oftentimes the goal is also to save money. Take the DIY stirplate as an example. A basic stirplate usually runs close to $100, but can be built from spare parts for less than $20.

I am usually combing the homebrewtalk forums for ways to improve my process. I began brewing about two and half years ago and quickly transitioned to all-grain brewing after doing two extract recipes. I have slowly upgraded my equipment and now do 10 gallon batches using two keggles and a cooler mashtun. I also invested in a keg setup and built a kegerator. In an effort to save costs on supplies, I began to incorporate many of the cost-saving measures well-documented on this site—buying hops in bulk, creating a yeast bank (first using slants now freezing vials thanks to a great article by Pete “PoppinCaps” Geisen), and buying grain by the sack. However, the immediate problem with buying grains in bulk is that you can no longer rely on the LHBS to crush it. So I bought a cereal crusher grain mill from Adventures in Homebrewing for $100. The cereal crusher, like most grain mills, comes with a handle for manual operation. But—much like bottling before it—I quickly found the process tiresome, especially after I began brewing 10 gallon batches.

Motorizing Your Grain Mill

So, as usual, I turned to the homebrewtalk forums for ideas on how to motorize my grain mill. The problem is that a grain mill requires a fairly low rpm, high torque drive. Some have just attached a drill to the drive shaft. Unfortunately, my cheap corded drill did not possess enough torque to get the job done without spinning at an excessive speed. I did not want to get another higher-torque drill (at least $50-$75) just to mill grain, and I was hoping to find a solution that allowed a bit more autonomy—i.e., where I would not need to hold the trigger down the entire time.

This meant installing the mill on a board with a dedicated motor. Most electric motors, however, operate at an rpm that is much too high to properly mill grain—usually around 1750 rpm. The most common solution for this problem is to use a belt and pulley system to reduce the speed down to a workable rpm. In order to do so, the pulley (technically called a sheave) affixed to the grain mill needs to be quite large, usually around 10 to 12 inches in diameter. While motors are fairly inexpensive (~$50 used) and easy to come by, you also have to buy pulleys (~$30-$40) and a belt. The other solution is to use a direct-drive motor that has a built-in gearbox that reduces the rpm. These gear motors are considerably more expensive, however, usually running close to $200. Although I had a ½ HP motor that was gifted to me, I was having a hard time finding the right pulleys locally. More importantly—having several young children who are keen on “helping” me brew—I really was not fond of the idea of having an open belt and pulley system. At the same time—again, having several young children—I did not want to spend the money on a direct drive gear motor. So, for the time being, I just continued to mill my grain by hand.

Fast forward to about a month ago, I was in my garage troubleshooting my daughter’s John Deere Gator toy car. After tinkering with it for a few minutes, I realized the problem was simply a loose battery lead. While I had it open, however, I noticed that each of the rear wheels was propelled by a small electric motor attached to a plastic gearbox. That got me thinking though—the wheels on the car turn at a nice steady speed, and the motor must have a decent amount of torque to propel the kids all around the yard. After a few moments of thought, I prudently discarded the idea of cannibalizing the toy car for parts for my grain mill, and decided to see if they were available online. A few minutes later and I had a link to the electric motor and gearbox sold as a single unit—for $23.50 shipped!

Link to Motor/Gearbox: Now $29.95 (was $23.50 when purchased in November).

A little additional research led me to an online forum where people “mod” the toy cars. Among a lot of other valuable information, I was able to determine that the 12V motor runs at an eye-popping 17,000 rpm, which is then drastically geared down to produce approximately 120 rpm and 150 inch pounds of torque. Although the rpm was on the lower end of what is the desirable range, the torque was excellent (the general consensus seems to be that around 50 inch-pounds of torque is needed to reliably mill grain).

Given the low cost—and figured that if it didn’t work out, at least I would have a spare motor for the kids toy car—I went ahead and purchased the motor. Because I wanted the spare in case it did not work out, I got the model that fit my kids’ car. There are other motor/gearbox variations available online (including 24V versions) that might produce a higher rpm. I opted against going with the 24V version because I did not have a readily available 24V power supply, and the 120 rpm produced by the 12V version was already faster than I could crank it by hand.

motor for grain mill

Looking at the pictures online and upon receiving it, I realized it would be a bit of a challenge to connect the motor to the grain mill. The motor/gearbox does not turn a driveshaft, but instead turns a plus-shaped cog that fits inside the toy car wheel, as shown on the image above.

After walking through Lowes for a few hours I was able to cobble together a potential solution. Basically, I took a PVC bushing and cut out notches that corresponded to the raised portions of the gearbox cog.

PVC bushing for grain mill motor

Link to PVC bushing:

I then screwed in some cheap black iron bushings, sequentially reducing the size until I was able to screw in a 1/8” brass nipple (it was not available in black iron at that size). The reason for the 1/8” nipple was that the diameter of the nipple was close to the diameter of the grain mill shaft.

Grain Mill Motor Shaft…itting/4331470
Not Pictured: Black Iron Bushing Fitting ¼ x 1/8 in (male/female).…tting/50380680 (actually is 1/8 x 1/8 threaded brass nipple)

The next challenge was to figure out how to mount and secure the somewhat awkwardly shaped motor and gearbox. I ended up mounting a metal plate to one face of the gearbox.

mounted motor for grain mill

I then cut out a slot into a wooden board, slid in the gearbox, and secured the gearbox by screwing the metal plate to some wooden braces I had screwed into the board. It is not pretty but it works. There are surely better ways to mount it; this is just the way I went about it.

Finally, the best method for attaching the drive shaft to the mill shaft would have been to use Lovejoy couplings. However, I am cheap and did not feel like waiting, so instead used a section of reinforced 3/8” vinyl tubing with a hose clamp on each shaft. Since the shafts directly abut, resulting in a short cross-section, the vinyl is able to handle the rotational force without tearing. However, it is my hope that if the mill became caught on a rock or other impediment, the vinyl might shear off rather than destroy the mill rollers.

diy motorized grain mill

The nice thing about the setup is that it runs on the 12V battery from the toy vehicle, for which I also have a charger. I just snatch the battery out of the vehicle and hook it up via alligator clips. Perhaps soon I will install an on/off switch as well. Because the mill is battery powered it is highly portable, and I could mill grain far from an outlet if the need ever arose. If you don’t have a battery, you could try to find a power supply, although it would need to be around 25-30 amps based on what I have read. Alternatively, I believe you could just hook the leads up to your car battery.

All in all, the project cost about $30.00. A short videos of the mill in action is available below. The batch of grain being milled in the videos was about 60% wheat and it started with a full hopper without the slightest difficulty.



36 Responses to “Cheap DIY Option for a Motorized Grain Mill”

  1. Traveler733 on

    This is great! Thanks for posting! I hope to try this, when the weather warms up. It is hard to control the speed of my drill. I keep a spare motorcycle battery, so this is doable for me.

  2. harrke on

    This was and awesome article. I had begun thinking about motorizing my mill and you have perfect timing! Thanks for the details and pictures.

  3. pricelessbrewing on

    How quickly does it go through 12 lb of grain?

    Not a fan that it’s battery operated and not outlet powered, otherwise I would probably go down the same route.

  4. BrunDog on

    Nice. I am surprised that little motor can do it at that speed. I have a unified DC motor/worm gearbox mounted to my mill… the motor is larger and the output is half that speed. Works great but I didn’t think much less would work.

    • bacgabe on

      I agree. I was surprised as well. Especially when you compare it to most setups with a 5-10 lb electric motor. It really does have a lot of power for its size. I couldn’t believe how small the motor was when I opened up the back of the toy car. I also figured it would hold up to a 5 – 10 minute grind every few weeks, considering the abuse it sustains on a weekly basis driving my kids around the yard, kicking it back and forth between forward and reverse, ramming things, etc.

  5. binabik on

    Nice article. I am looking at motorizing mine, however I am repurposing an old shredder motor. It has plenty of torque, already has an on/off switch and runs on120 V. I can also repurpose the sensor to automatically stop the motor when completed.

  6. bschot on

    I found this link: and in the comments someone said that the motor only pulls about 2.2 amps when running. If that is the case finding a 12V power supply would be a piece of cake; in fact I found a 5 amp model on Amazon for $11.50 shipped. I think if I end up using this motor I’ll use a battery and an ammeter to see the draw and purchase an appropriate power supply.

    • bacgabe on

      That would be great if that’s the case. You’re right, power supplies in that range are easy to find. I really need to measure the amount of current it pulls on my next grind. I’ll report back when I do.

      • bacgabe on

        I ran some more grain through it last night while hooked up to my multimeter. Without any load it runs at about 1.7-2.0 amps. While grinding basic 2 row it pulled about 3.5 amps. I put 100% wheat in it to give it a real exercise and it pulled about 5 to 5.5 amps. My gap setting is around .34. So IMO you should be good to go with a 5 amp power supply.

        • bschot on

          Sweet, that is really promising. I looked on Amazon for a 6 amp power supply and it looks like they are little cheaper than the 5 amp models, 10 amp models are about $20. I had a thought, what is the peak draw on starting with grain? I know the lead/acid or lithium batteries can handle the momentary high draw but I don’t know if the power supplies could handle it. It may not be that big a deal, just start the mill and then pour the grain in.

  7. jimdkc on

    I’m going to try this too. Should be pretty easy to adapt to AC power. There is no way that little motor draws 25-30 amps! 2-3 is much more likely! I’m pretty sure I have a 12VDC 4A power supply around here somewhere!

    • bacgabe on

      You’re exactly right! I should have done a bit more testing before posting the article. The motor draws about 3.5 amps on a typical grind.

  8. rekoob on

    Nice article. I have yet to motorize my mill but have thought about it a time or two (I do use a drill).
    I will keep this info in the hopper for future reference. 😉

  9. fosaisu on

    Love the MacGyver approach to the problem. And just think you’re probably one of the few people on earth milling beer grain on battery power!

    For anyone considering powered milling, a high power 1/2″ corded drill from Harbor Freight will run you ~$40 with the ubiquitous 20% off coupon. You’ll need a carriage bolt and some scrap wood shims to mount the drill at the proper height. But given that this build requires a number of connectors, it’s probably not much more expensive to go with the drill, and you also get a powerful tool that will make quick work of your next backyard carpentry project. Of course if you’ve already got one of these motors lying around, it’s the much cheaper way to go! And more of a conversation piece for sure.

  10. plan_ahea on

    Awesome project. I did some looking online for something like that in Canada, and I found your motor/gearbox, for $45… Any tips for finding something cheaper on amazon/ebay/aliexpress? (Keywords, websites, etc.)

  11. bupalos on

    Hey just another option that is maybe a little less costly and involved, I just spent 4 hours playing around with converting a pasta roller before coming up with something that works really well and would have taken me 10 minutes if I had tried it first. All I’ve done in the end is remove the scrapers that press up against the rollers (5 minutes) which allows me to put one layer of textured cloth tape on each roller. The textured tape is required for the smooth rollers to suck in the grain. On this Imperia roller on the “1” setting and adding the thickness of the tape I end up with a .038 gap (measured by 1 mil card stock and .2 mill paper and I think there’s even a little bit of “cushioning” to the crush and less shred than my buddy who’s got one where he textured the rollers by running a drill bit all over it to kind of rip them up. It’s as good a crush as I get from the LBS. It might be marginally better, or I might just be in love with my own baby. I’m stoked! Made a little hopper just taped up out of coroplast and hooked it on with mini-bungies that does the trick, that took maybe 1/2 hour.

    For motorization you can just stick a beefy 3/8 flat sided drill bit in the rectangular receptacle than accepts the crank and let it rip, probably wouldn’t want a high-speed drill, my cordless dewalt turns it about the speed you want to go and does me 10 lbs in about 5 minutes. Or just crank it if all the drinking hasn’t already ruined your elbow.

    Pasta roller can be had for 25 bucks (or 3 at a garage sale), roll of textured cloth tape is 3 bucks, you’ve got the drill. It’s a really great crush. Extra advantage (in my case) that I used our existing pasta roller and I can tell the wife if we ever want to make pasta (which is like once a year, tops) I can just pull the tape off, and put the scrapers back on, I haven’t wrecked it for it’s original purpose.

  12. MagicMatt on

    Just curious, but I noticed you said the grain was about 60% wheat…….you don’t mill your wheat separately, with a tighter gap?

    I made the mistake once of mixing the wheat with the barley and milling it all at the same gap. What I got was perfectly milled grain and mostly untouched wheat.

    Now I set my gap for normal grain at 22 mil and for wheat at 12 mil, and never been happier.

    • bacgabe on

      Interesting. It never occurred to me to mill them separately, but you do have a point. I guess I never noticed enough of a hit to my efficiency to think of it. I may give that a try. Thanks.

  13. bruce_the_loon on

    Has anyone tried using a windshield wiper motor, those are 60rpm and 50-70 lb-ft torque and run off 12V DC well. 2nd hand ones from a scrapyard should be $10-$20 at the most.

  14. N3Bruce on

    I was thinking a power supply from an old desktop PC might do the job. I picked up the smallest one I had laying around (in this case a 250 watt ATX supply) and looking at the rating label, it says it is good for 8 amps on the 12 volt section. Just pull the yellow and black leads off of one of the Molex connectors for power. If your power supply has no switch on the back, you will need to wire the green wire going to the motherboard connector to a black wire to a switch. If the supply does have a switch, you will need to tie a the green wire to a black wire, then use the switch to turn the motor on and off. If you are using an ancient AT supply, verify the 12 volt section has adequate power, then just tap a yellow and black wire off of a Molex connector.

  15. N3Bruce on

    I was thinking a power supply from an old desktop PC might do the job. I picked up the smallest one I had laying around (in this case a 250 watt ATX supply) and looking at the rating label, it says it is good for 8 amps on the 12 volt section. Just pull the yellow and black leads off of one of the Molex connectors for power. If your power supply has no switch on the back, you will need to wire the green wire going to the motherboard connector to a black wire through a switch. If the supply does have a switch, you will need to tie the green wire to a black wire, then use the switch to turn the motor on and off. If you are using an ancient AT supply, verify the 12 volt section has adequate power, then just tap a yellow and black wire off of a Molex connector.

  16. KudzuHighlander on

    Sweet idea, my uncle used a treadmill motor (there will be lots of those for sale soon). The motor is DC and “dashboard” has variable speeds built in. I think is paid $10 for it at a yard sale.


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