Mac's Shop Marble Mills

Home About Me Random Musing on Sphere making Pre-forming With Core Drills Marble Mills TUMBLER PLANS Machines for Sale Other sphere machine and plans Diamond Wire Saw Beads Contact me		Marble mills use a centuries old technique to make several marbles or beads at one time.  Contrary to what I've read, it seems quite possible to mix rocks of different hardnesses with good results.  I have loaded the machine with garnet and emerald and it worked just fine with them all getting round at the same time.  The grinding pad can be silicon carbide or diamond depending on the material.  However, the granite and marble polishing pads that come in sets to polish floors and countertops do not work at all in this mill.  This particular marble mill has a groove in the bottom plate that forces the marbles to move in a circular path while the top plate is an abrasive pad the grinds away at the uppermost part of the bigger marbles.  Eventually the marbles are worn round and to the same size.  The gearmotor turns at about 60 RPM which is just about right.  The grinding plate can be a cheap 6" silicon carbide pad or a somewhat more expensive diamond lap.  By putting the mill in a pan, water can be added to cover the marbles and the mill will happily run for hours and hours.  I find this machine to be fun to use, but it is a bit tedious making up a load of roughs.  They do have to be round enough to roll rather than slide and they should be close to the same size.  This picture shows 2 bottom plates with different grooves illustrating some of the possibilities.  The marble mill can make a dozen marbles or as many as 30 beads at one time.  I actually have not tried to make 30 at one time because of the tedium involved in getting 30 small rocks round enough to go in the mill.  The most that I have done at one time is 12.  The rocks need to be round enough to roll rather than slide and, since they will end up the same size, it helps if they are close to the same size to start with.  Like I said, tedious.  However, once the mill is loaded, it requires very little tending.  As you can see, it is possible to build a miniature version of the marble mill to make 5 to 10 small beads at one time.  The grinding disc is a diamond disc 1.75" in diameter.  The center hole was enlarged to allow mounting with a #6 machine screw.  This little mill takes up very little room.  My experiments have indicated, however, that when there are too few marbles in the mill, there is a tendency for them to be egg-shaped instead of round.