[doug_1279]

and to think that in the near future, a 3-D Printer holding and squirting hot molten bronze metal can do the actual piece in one day. (you do great work - keep it up).

The impellor would be ideal for the method you mention due to the extra complexity it takes to mold then cast one with its twisted blade shape..
Printing can also go a step further with blade designs that are optimal to the point where they become impractical to make any other way.
The best method is always a balancing act of many variables, I see sand casting holding a place in that equation for many years to come for the right mix of numbers required from relatively cheap tooling..

 

[doug_1279]

Latest project up on the table.
Don't know where the boss finds these job's that fit between the columns by millimeters.