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How to Build a Large Rock Tumbler

Tumbled stones are lustrous, smooth and rich in color. They are popular in jewelry and as household ornaments. Refining a batch of them from more ordinary stones requires a large rock tumbler. A rock tumbler is three shafts and a motor mounted on top of a wooden frame. One shafts is attached to the motor and spins a barrel filled with rocks. The construction process involves screwing the wooden frame together and then mounting the mechanical parts onto the frame in the correct positions. Then you just plug it in and tumble away.

Things You'll Need

1750 RPM Motor
4 surface-mount bearings
2 8-inch shafts
2½-inch pulley
8-inch pulley
Pulley belt
2 28-inch 2-by-4s
24-by-28-inch sheet of plywood
24-by-14-inch sheet of plywood
12-inch diameter by 20-inch length barrel
Screwdriver
Wood screws

Instructions

- 1
  
  Drive the wood screw through the 2-by-4 and into the plywood
  
  Place a 2-by-4 along the 28-inch edge of the larger sheet of plywood. Screw it into the plywood with one wood screw on each end of the 2-by-4 and one in the middle for added stability. Do the same with the other 2-by-4 on the opposite 28-inch edge of the plywood. You should have a 24-by-28-inch sheet of plywood with a 2-by-4 screwed along each of the 28-inch edges.
- 2
  
  The smaller plywood sheet fits over exactly half of the larger sheet.
  
  Lay the smaller sheet of plywood on top of the 2-by-4s and along one of the 24-inch sides of the frame. It should cover exactly one-half of the frame. Screw the smaller sheet of plywood into the 2-by-4s with a wood screw in each corner. Half of the 2-by-4s will be exposed.
- 3
  Screw two surface-mount ball bearings into the exposed half of one of the 2-by-4s. They should be 9 inches apart from each other. Do the same on the other 2-by-4. The bearings should be positioned equivalently on each 2-by-4 so that the shafts can go through them.
- 4
  Mount a shaft through two bearings that face each other on opposite 2-by-4s so the shaft is perpendicular to the frame. Mount the second shaft through the other set of bearings in the same way. The shafts should extend over the 28-inch edge by 4 inches and be parallel to each other.
- 5
  Screw the motor into place on top of the smaller sheet of plywood with four wood screws. The shaft of the motor should also extend 4 inches over the 14-inch side of the smaller sheet of plywood, perpendicular to the frame, and all three shafts should be parallel. The shaft closest to the motor shaft is the drive shaft and the one farthest away is the free shaft.
- 6
  Place the 8-inch pulley on the drive shaft and the 2-1/2-inch pulley on the motor shaft. Connect them with the belt. Make sure the belt is tight. Rest the barrel on the two shafts mounted to the ball bearings, hook up the motor and start tumbling.

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