How to Make Models of Joints

Carve the ball of the joint and the connecting bone carefully cut from a block of bass wood. The ball of the joint should be very smooth and approximate a sphere. Use sandpaper to finish the joint. Alternatively, screw a small wood sphere, available at hobby stores, to the bass wood block or to a wood dowel to simplify the construction of the joint. Ensure the wood screw heads sink into wood, without extending above the wood surface, to avoid additional friction in the joint.

Melt paraffin in a small pot on the stove. Follow the instructions provided on the paraffin container to melt the wax into a consistent liquid state, without solid particles. Lower the stove temperature to cool the paraffin wax slightly. Dip the spherical ball of the joint into the wax many times to create a coating approximately 1/16 to 3/32 of an inch thick on the ball. Turn off the stove and allow the wax coating to cool for an hour or more.

Construct a mold for the socket of the joint using cardboard coated with layers of packing tape to seal the mold. Approximate the shape of the joint to add realism to the joint model. If necessary, create multiple, connected molds until you cast a realistic joint.

Pour fresh, uncured plaster into the socket joint mold. Follow the instructions provided with the plaster to create the best consistency for the mix. Place the paraffin wax-coated ball of the joint into the mold. Ensure only the paraffin-covered portion of the ball is submerged in the plaster. Allow the plaster to set, supporting the ball to limit motion in the joint while the plaster cures. The plaster should take 24 to 48 hours to cure.

Heat the wax that is coating the ball of the joint with a heat gun until the paraffin melts away. Orient the socket upside-down to allow the melted wax to drip away from the socket. Slowly move the bass wood or dowel to work the joint and remove the remaining wax. The joint model should work just as the natural joint.

Tool the form of the plaster socket with a rotary tool to create a more realistic joint. Remove small amounts of the plaster with each pass of the rotary tool; do not attempt to remove great masses from the plaster, which can crack or damage your joint model.