I just finished a small project that needed a core to make the inside hollow and at the same time fairly smooth.
The end result was a ball mount for an old tractor light.
The ball shape is about 3" in diameter. The slot in the ball is for tightening up the light bolt with a wrench.
I started with a turned wood pattern, that I put in a plaster of paris mold.
Then I used ceramic slip to pour in and then drained out after it had set for about an hour.
The resulting core was then put in a small electric kiln and heated to 700 F.
It was not enough to make it rock hard, but it dried it out enough that 720F zinc wouldn't make it POP when poured.
It also is easier to remove if not cured too hot.
This is a very inexpensive way to make a good core.
Ceramic slip is about $4.00 a gal. The plaster of paris is cheap also.
The picture shows the progress from wood pattern to finished casting.
The part was originally made in cast iron and when this is painted and installed, that is what it will look like.
