Sprue design quiz: test your knowledge on getting optimal fills when casting
By J. Tyler Teague
Many factors must be taken into consideration when designing a sprue or feed system for a model, the most important of which is the alloy you are casting. Platinum group alloys are typically considered the most difficult to cast because the metal purity (950 parts per 1,000) causes more shrinkage and gives you less time to fill the cavity in the mold before the metal solidifies.
Regardless of which alloy you are using, if the casting doesn’t fill, it doesn’t count. Also, if the casting is full of shrinkage porosity and requires more labor to fix than the profit you’ll be making from the part, it doesn’t count either.