Pictures of a ball mill rack that you can make yourself
No industrial plant that mixes its own raw glazes would be without a ball mill. Yet potters lack them for a couple of reasons: Expense and awareness.
A ball mill is a porcelain jar a little more than half filled with porcelain balls (they can also be alumina or natural stones). Glaze is poured in, a lid secured, and it is rotated on a motorized rack (often for hours). The tumbling of the balls within grinds particles smaller and smaller. The creamier glaze applies better, has more stable viscosity, fires more consistently and cleaner with less specks and imperfections (eg. pinholes and blisters), and melts better. Ball mills also enable you to employ native materials.
Jar: Jars need to be heavy and strong. They are expensive, a 1 gallon jar typically costs about $100 US and weighs 15+ pounds. These jars are not easy to make. They must have a water tight lid. A jar must be a true cylinder or it won't rotate without hopping in the rack. They are not glazed on the inside. They are best made by casting a low shrinkage porcelain (it would be extremely difficult to dry and fire a thick thrown perfect cylinder shape made from a plastic porcelain). Typically small jars have a range of ball diameters from 1-4 cm. The pebbles cost about $6 US per pound and you need about 10+ lbs for a 1 gallon jar.
Rack: A rack (or stand) costs $700-1300 US. However you can build your own for much less.
Front and Back View
Unit weighs about 50 pounds. The lower assembly is welded from angle iron, the upper from 1/8" flat steel.
One rod is longer and extends out the other side of the bearing for the large pulley to mount on. It is driven by a 1/4 hp 1725 rpm electric furnace motor (this type of motor is mass-produced and inexpensive). The motor does run quite warm.
Pulleys & Rollers
The pulley ratio is about 5.5:1. The large is a self locking mount type. The rotating rods are 1" cold roll. Hydraulic hose with slightly less than 1" inside diameter has been pulled over the rod to grip the jar and make it run smoothly. Apply grease to the rod if the hose is difficult to pull on.
Use a caster wheel welded sideways at both ends to keep the rotating jar on center (the jar needs an unobstructed shoulder to ride against these casters).
Four pillow block bearings hold 1" cold roll steel rods in place. The rods are far enough apart so that the shoulder of the jar runs low enough to contact the caster wheels.
Legs and Feet
Thread bolts into the feet as shown so the rack can be leveled and to prevent it from rocking on the floor.
You can use a vertical-sided plastic jar in a pinch, the grinding action between the jar walls and balls is lost but the balls will still crush the particles between them if you mill for longer periods. Wine making carbuoys are good also since they are very straight cylinders that will roll without hopping in the stand.
The jar must be cylindrically true or it will rock and hop while turning.
Fill the jar 55% with balls.
The jar should not turn too quickly (about 30 RPM).
Ball mill jar and rack made by @andygravesstructures
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Ball milling A method of grinding particles in ceramic powders and slurries. A porcelain, metal or rubber vessel filled with pebbles tumbles and particles are ground between colliding pebbles.