How To Rotocast Resin for Lightweight Displays


Jacob Johnston of Little Rock, AR, was contracted to supply 250 bust replicas of President Bill Clinton for the opening of the Clinton Presidential Library in Little Rock, AR in November 2004. The castings had to be lightweight and be able to be handled and dropped without breaking and Mr. Johnston was convinced that rotational casting these pieces was the way to go. His original prototypes were rotationally cast by hand in plaster, and even though hollow, the customer rejected plaster as being too heavy and fragile. But hand rotationally casting plaster for production of 250 pieces would also take a long time and this project most definitely had a deadline. There had to be a better way.

After contacting the Smooth-On technical help line, he narrowed his options down to two materials: Task® 15 and Smooth-Cast® 65D. Not needing the high performance properties (and cost) of TASK® 15, he decided to try Smooth-Cast® 65D. Mr. Johnston rented a rotational casting machine for producing the castings. What remained was creating the final sculpture and mold. 

The original model was sculpted in clay and Brush-On® 40 mold rubber was used to make the rubber mold. Plasti-Paste® support shell material was used to make the mother mold with 2 x 4 pieces of wood being imbedded to make level supports.

With the rotational casting machine set up and ready to go, Mr. Johnston determined the optimal amount of Smooth-Cast® 65D resin to be used in the mold to generate a uniform hollow casting surface.

Smooth-Cast® 65D performed flawlessly, yielding hollow castings that looked as though they were cast solid but weighed just under 2 lbs. (0.9 kgs) each. All 250 castings were then back filled with Foam-iT® 5 rigid foam to provide lightweight support and additional impact resistance. Each pieces was then painted and delivered in time for the opening of the library.

Mr. Johnston calculates that he saved thousands of dollars in material and labor costs by rotationally casting these pieces.

Materials Used in this Tutorial

Step 1: Preparing Mold For Casting