If you've been to a home brewing supply store or happen to grind your own grain then you know how loud grain/barley mills can be. I built this setup for Company Shops Market, my local cooperative grocery store when they started carrying home brewing grains in the bulk food section (best idea ever, now I can grocery shop and pickup brewing supplies in one trip). The problem was that a traditional bare-bones grain mill and power drill setup would have caused too much noise for the peace and quiet of our neighborhood grocery store. This setup cut down the noise from the mill by 12 dB. It's still noisy, but it doesn't resonate through the whole store anymore. A friend of mine built the wooden box and platform. Adding the noise canceling Sorbothane bushings, acoustic sheets and mounts took about an hour.
Most grain mills come with a hand crank. Removing the crank arm exposes the shaft which usually fits into the chuck of a power drill. In this installation we used a pretty standard 120V corded power drill. Lots of torque but lots of noise too. We built a wood box with a variable speed controller to allow for easier operation. The controller plugs directly into the stock cord of the drill. This controller allows the mill to operate at lower speeds which is better for the grain and noise. The whole setup is mounted on a wood shelf which will be installed near the bulk food section of the grocery store and allows a 5 gallon bucket to sit under the mill to catch the grain.
The most important part of any vibration isolation project is fully decoupling the vibration source from the structure. In this case we are isolating the mill and power drill from the shelf. To float the mill above the shelf I used 3/4" diameter Isolate IT Sorbothane hemispheres. 4 of these gave me a nice stable base to set the mill on. I used the urethane coated version because milling creates a lot of dust and the coating will keep the dust from sticking to them. Raising the mill will create a gap between the shelf and crusher so I added some 1/2" foam weather stripping to keep grain and dust from collecting in the gap.
Next we need to keep the mill from moving around but still allow it to float above the shelf. Again the key is to prevent any direct contact between the two structures or any of the solid fasteners. To do this I used Isolate IT Sorbothane 0510005-50-12 bushings. These fit 1/4" bolts and have a nice shoulder on the bushing that keeps the fastener from contacting the mounting plates. I drilled 1/2" holes to fit the bushings into. You can also get them with a deeper shoulder, that Isolate IT part number is 0510002-50-12. Either would have worked for this project. Make sure to use 1" metal washers with the fasteners to keep them from pulling through the Sorbothane bushings. Tighten the bolts so that they compress the Sorbothane by 20%. This gets it into it's sweet spot and isolates the most vibration. I used 50 durometer (softness) bushings and hemispheres for this project. You can use 30 (softer) or 70 (harder), since the fasteners can be tightened to create/adjust to the correct compression (load), the listed load ratings for the bushings can be ignored.
Since most of the noise originates from the power drill, I decided to add Isolate IT Sorbothane X-Tra Flex acoustic sheets to the inside of the drill box. This was also the best way to isolate the drill. The Sorbothane X-Tra flex sheets are 3/16" thick and have an egg-crate dimple on them. We used the softest durometer available, 40 duro (Shore OO) as this absorbs 40 dB per 1cm thickness of material. The dimple pattern also creates destructive acoustic interference which further decreases the noise level (granted not by a huge amount, but anything helps). The sheets come in 12 x 14" and can be cut with a scissors. I used Loctite High Performance Spray Adhesive to bond the Sorbothane to the wood. It worked pretty well, just make sure to clean the Sorbothane with rubbing alcohol before applying the adhesive. Apply as directed and allow the full dry time.
Make sure everything lines up and that there isn't any wobble in the drill when it's spinning. We heard a 12 dB reduction in the noise from the mill following this upgrade. A lot of that was from the decoupling of the mill and shelf which prevented the whole shelf from resonating every time we ran the mill. I'm been home brewing for over 5 years now and every time I visit a brewery I love checking out their equipment. Here are some photos of a grain mill that I saw in Amsterdam. They also used vibration isolating feet on their grain mill to help reduce the noise and vibration. If you've got a big mill like they do, a simple option is Isolate IT Sorbothane Anti-Vibration Leveling Feet.