DIY Rock Tumbler
My wife recently started making beads and other things from polymer clay, and wasn't getting quite the finish she wanted using sandpaper. It turns out that even children's toy rock tumblers are relatively expensive and the professional models are definitely out of our price range, so she asked me to see if I could assemble something from old bits and pieces we had laying around.
The kind of tumbler I've seen before seemed like a fairly simple arrangement — some kind of barrel turned by horizontal rollers, similar to a tumble dryer, so that's what I set out to build.
Parts list — these parts all came from my junk pile. Nothing was purchased for this project, so technically it cost $0 to build. As suggested by several people (iceng and ottwafm), the tumbler would be more durable if some kind of wheel bearings were used for the rollers. Bearings for skate board wheels or ride-on mower decks should be easy to find locally.
1) electric motor from Grand Am electric window lifter.
2) old PC power supply. This one happens to be a 90W supply.
3) rollers — could be broom handle or any round pole. These are actually mini rolling pins from my wife's craft supplies.
4) various bits of wood to make a frame and base board.
5) 2 inches of garden hose.
6) power switch.
7) screws, coach bolts w/ nuts
8) anti-slip shelf liner
3) Drill + appropriate sized bits
5) Sharp knife
6) Soldering iron (or use crimp-on spade connectors)
Cut several length of plank to make the ends of the frame, then stand them in their approximate locations. The position of the driven roller depends on the size of the motor mount. The position of the other roller is variable, depending on the size of the drum. The rollers here are 5" apart on centers. Later I decided to add a third roller at 3.5" to accomodate smaller drums.
The holes for the rollers are somewhat oversized. This should eliminate binding and the weight of the drum will hold the rollers down. The large hole is for the garden hose that connects the drive shaft to the roller.
The motor is built into its own mount, which is offset from the side of the motor, so I cut a shim out of a piece of scrap plywood.
The static end just has holes for the rollers. The slot above the middle hole allows the roller to be removed when a larger drum is being used. In fact, a single non-driven roller could be used, with multiple slotted holes to suit different drums.
Check the Spacing
The spacing between the ends depends on both the size of drum and the available rollers. These are ready-made rolling pins, but broom handle or other round stock could be cut to length.
After measuring the separation for the ends, rails are cut and attached. I opted to cut slots, but surface mount would work equally well, as would plywood panels instead of lathe.
Mount the motor along with the driven roller. I used coach bolts, which present a rounded head in the roller section.
The roller ends have a small amount of furniture finishing wax applied, to reduce friction in the holes.
Take a look at the PC power supply cabling. There should be a single green wire going into the big connector block. That's the "power on" wire — it enables the motherboard to switch off the power supply when the PC shuts down. Clip that wire and one of the nearby black (ground) wires. Connect those to the power switch (any switch will do). I soldered mine rather than buying spade connector clips.
Next, take one of the flat, 4 pin connectors and clip off the yellow (12 volt) and black (ground) wires. Solder those to the motor. I cut away the connector shroud to be able to get the soldering iron into it. Again, spade connectors would work, as would the proper connector if available.
Plug in the power supply, flip the switch and watch the roller turn!
Tidying Things Up a Bit
1) clip off remaining wires. I wrapped each end in tape, then bundled them with more tape.
2) screw the frame to the baseboard.
3) secure the power supply. I had a length of pipe hanging strap available, which also sufficed to hold the power switch. I oriented the power supply with the fan blowing towards the motor to provide cooling.
4) I had some spare storage drawers that just happen to fit nicely on the other end of the base board.
5) tests showed that the barrel would sometimes slip, which is why the rollers are now covered in anti-slip shelf liner.
Test Run on Assembled Frame
First trial run — the glass jar originally contained a candle. It has a plastic ring that makes a good, tight seal. The jar contains a few beads and a slurry of water and sand. This would eventually achieve the desired result, but it demonstrated the need for some kind of internal vanes to "lift" the mix as the container rotates.