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.
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.
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.
Not Pictured: Black Iron Bushing Fitting ¼ x 1/8 in (male/female).
https://www.lowes.com/pd/BrassCraft-…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.
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.
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.