I've been using lead shot and epoxy for over two decades to add strength and mass to hollow plastic and die cast metal parts of tools. I use #9 lead shot (steel shot could be substituted) to add mass to lightly molded parts. The epoxy doesn't need to be high strength as it's being used to encapsulate the shot in the cavity, so pourable resin works fine. The epoxy binds and seals the shot into the cavity(s) of the part. The fineness of the shot allows it to fit into odd or irregular shaped cavities without an special molding. The sides of the cavity have small recesses cut into them to key the epoxy to the part. Multi part assemblies need to have joints sealed with CA glue to keep the epoxy from leaking out until it sets. The pourable (or casting) epoxy is introduced by pouring it into one end or side of the cavity and allowing it to flow down and across the cavity until it is full. This forces out any air between the shot eliminating bubbles which strengthens the infill. This method is an easy way for users to make cheap parts far more usable and long lasting. The application is limited only to the imagination of the tool owner.

Some plastic knobs from my bandsaw and CMS filled with the matrix.



A two part table saw tilt/elevation crank strengthened with the mix.




A 12 oz. die cast aluminum lathe tailstock filled with 5.5 pounds of the matrix. Also the bottom clamp and plastic locking lever which received the infill.




The lower bed rails of a shop built lathe filled with the matrix.