Motorize Your Grain Mill


Like many, I started out with extract, moved to extract with specialty grains, partial mash, then all-grain. Up until I reached partial mash, I used zip-top bags and a rubber mallet to crush my grain. When I reached partial mash, I found I could not continue my process and had the local homebrew shop crush my grain. Worried about my crushed grain going stale and consistency of the crush, I wanted my own mill.

I purchased a Monster Mill 2 and began making plans, scrapped plans, and made new ones. Rinse and repeat. Five years later, I finally finished and ran grain through it for the first time.

Monster Brewing Hardware, makers of the Monster Mill, suggest running the mill at approximately 150 rpm. I initially looked to follow suit of many brewers with a standard farm duty (or similar) 1725 rpm motor (available at many retailers) to drive the mill using a belt and sheaves. This would require a small sheave (driven pulley) on the motor with a large sheave (12+ inches/30+ cm diameter) on the grain mill. I did not like the idea of such large sheaves. Others also use low-speed drills to drive the mill, but these are a pain not only to mount, but also to maintain the proper speed. I also looked at a gear system, but I could not locate an inexpensive set for low horsepower motors. It then occurred to me that there is a piece of equipment that many of us use every day, is inexpensive, and has a gear system built in — a garage door opener.

Chain drive garage door openers are typically in the 1⁄2 to 1 horsepower range. They operate with a worm gear on the motor shaft, which turns a gear on a secondary shaft attached to the chain sprocket. This would be perfect. To the best of my knowledge, belt drives also operate the same way. Screw-drive openers, however, will not work.

A major obstacle was how to attach the mill to the opener. Because the opener and the mill had two different shaft diameters, I chose to use a Lovejoy connection. They are removable, allow for some slight misalignment, and can absorb a small amount of torque in case a rock or something makes its way to the rollers.

Another obstacle is to rewire the opener to run continuously instead of the short distance to lift or close the garage door. I removed the circuit board and wired the motor directly to relays (details in the step by step).

The last major obstacle is heat. Garage door openers are only designed to move the door a few times an hour. To crush 12 lbs. (5.4 kg) of grain, it needs to run continuously for upwards of five minutes. I chose to place a fan in the bottom of the opener to blow air up through the motor.

As of today, I have crushed around 36 lbs. of grain without any issues. As the gears are plastic, I will keep an eye on how they wear. If (or when) they get bad enough, replacements are available for under $20.


Garage door opener (chain drive)
Monster Mill and hopper
Lovejoy 10208 L050, .375” bore (mill side)
Lovejoy 10210 L050, .5” bore (motor side)
Lovejoy 37786 L050 coupling spider
5VDC cell phone charger
2-channel relay board (, Item 144140)
2 switches, SPDT
Project box
Replacement extension cord plug
115VAC 120mm muffin fan
Dust covers for fan
3⁄4-inch plywood or orientation
strand board (OSB)
2×1 and 2×2 boards
5-gallon (19-L) bucket