CNC frame rock tumbler

Heavy duty rock tumbler / barrel rumbler

Polish rocks or metal 3D printed parts!

This design uses a mains powered AC synchronous geared motor which runs quietly and reliably for long durations.

The barrel is made from cheap, durable PVC plumbing components and can be optionally lined with rubber or a printed insert. Mine is lined with checkerplate rubber sheet.

Note that I am in Australia. Barrel parts are available from Bunnings 'Holman' brand. Electrical parts from Jaycar. The motor and rubber mounts are from eBay and the O-rings came from a kit from Aldi.

Bill of materials

Frame

• 6 parts, CNC cut from 18mm plywood
• Cover plate, from thin acrylic / aluminium etc (I used 2mm clear acrylic).
• 10 x 10G x 30mm wood screws
• 4 x small self tapping screws approx 3mm x 10mm long for cover plate

Printed parts:

• 4 x drive wheels
• 1 x motor pulley
• 2 x shaft pulleys
• plug to cover motor shaft hole
  (STL is included with all parts for printing)

Hardware - barrel:

• 2 x 100mm PVC threaded access coupling (105mm long overall)
• 2 x 100mm PVC screw on cap
• Short length of 100mm PVC pipe
• PVC glue / primer

Hardware - mechanism:

• Motor - AC Synchronous geared 100RPM 60mm x 60mm
• 4 x M4 15mm x 15mm rubber mounts, Male - Female threads
• 4 x M4 x 25mm machine screws
• 4 x M4 nyloc nuts and washers
• 1 x M3 grub screw + nut (for motor pulley)
• 2 x 300mm lengths of M8 threaded rod
• 20 x M8 nuts, 13mm hex (I used 8 x nylocs and 12 x plain nuts)
• 4 x 608ZZ (skateboard) bearings
• 2 x O-rings 50mm ID x 3.55mm for drive bands
• 4 x O-rings 28mm ID x 3.55mm for drive wheel tyres

Hardware - electrical:

• IEC power socket + fuse + switch (optional)
• Mains power cable
• Wire, lugs, solder, heatshrink etc.

Instructions

1. Barrel

• Measure the distance inside the threaded access coupling up to the ridge, from the non-threaded end.
• Cut a length of 100mm PVC pipe just shorter than twice this distance.
• Assemble the 2 couplings to each other with the pipe, using PVC glue (primer optional).
• Screw on the end caps.

1. Frame

• Cut all 6 parts from 18mm Plywood
• Contersink screw holes if preferred
• Assemble frame with screws
• Rout a rebate around the inside of the underneath of the motor box, to fit the cover plate. I used a 9.5mm rebate bit, 30mm diameter, 5mm deep using a hand router.
• It is easier to take the outer ends and lid back off the frame for the remainder of the assembly.

Notes:

• All cuts can be made with a 6mm tool except for the 4 x motor mount holes which are 4mm diameter.
• Outer pockets for 608 bearings are 7mm deep
• Outer pocket for IEC power socket + fuse + switch is 16.5~17mm deep, allowing the clips to hold on the thin ridge left.

1. Mechanism

• Press M8 nuts (preferably nylocs) into the drive wheels and shaft pulleys.

• Press 608 bearings into the outer end frame and inner end frame.

• Push the motor shaft plug into the inner end frame.

• Thread drive wheels, lock nuts and bearing nuts onto the shafts (see photos).

• Insert shafts through the bearings in the inner frame end.

• Fit the outer end frame with the shafts poking through the bearings.

• Fit M8 nuts (preferably nylocs) to the outer end of the shafts.

• Fit M8 plain nuts to the inner ends of the shafts, plus an extra plain nut to lock the shaft pulleys.

• Adjust the position of the drive wheels so that the barrel fits properly.

• Fit the shaft pulleys onto the shafts.

• Fit the motor pulley to the motor with the grub screw and M3 nut. Note the boss goes towards the outside end of the shaft.

• Attach the 4 x rubber mounts to the frame with M4 x 25 screws.

• Loosely place the drive bands and fit the motor to the rubber mounts with washers and nyloc nuts.

• Adjust the shaft pulleys to align to the motor pulley.

• Tighthen all lock nuts.

1. Wiring

NOTE: This design uses mains voltage, which is dangerous! It may be illegal in your country to wire this yourself. Do not attempt to wire this unless you know what you are doing!

• The motor has 3 terminals. The middle terminal is Neutral and the outer terminals are each active, for a different rotation direction. Connect the active to only 1 of the outer terminals and leave the other one unconnected.

• If you are using a metal cover plate, it is a good idea to connect the Earth wire to it. Otherwise, connect Earth to the motor housing via one of the mounting screws.

Fit the rest of the frame plus the cover plate with 4 x small self tapping screws before operating.