Shooting using cast bullets can lead to a dirty cartridge. The burnt gun powder, sizing lube and cast bullet lubricant can build up along with general dust to clog the cartridge. This can lead to feeding and extracting issues and will make it difficult to see cracks in the necks and head splits. Case tumblers will clean your cases to prevent these problems. You can make a tumbler to help leave your cases sparkling.
Alter the motor. Cut a piece of wire about 2 feet long and use it to wrap a small weight (you can use an old bullet casing) to one of the blades of the motor fan. This will unbalance the motor causing a vibrating effect.
Construct the platform. Take the 1 foot square of medium density fiberboard and place the ice cream bucket on top. Trace a circle around the bucket with a pencil then remove the bucket. Nail your plastic tubing along the circle so that it is the exact circumference of the bottom of the bucket. The bucket should fit snugly within the tubing.
Bolt the platform to the top of the motor. Place it securely so the vibrations will not cause it to unscrew.
Place the motor on top of the other piece of medium-density fiberboard as a base. Draw an outline about an inch from the edges of the motor. Nail plastic tubing along this line. The motor should fit inside the tubing with plenty of room to vibrate.
Fill your ice cream tub with either crushed walnut shells (traditionally used) or rice, leaving just enough room for the casings to fit in.
Put it all together. Fit the ice cream tub onto the platform and place the motor on the base. Add your cases to the walnut shells or rice and fit the lid on tightly. Turn on the motor for about two hours and let it tumble.