I have a bunch of castings to mill on a horizontal which are tubular in shape but arent straight, they bend around into different angles and elbow shapes. The ends are the only thing needing machined. So i was thinking about making some fixture pads out of concrete to clamp the parts down onto using a part to make the mold with. There are dozens and dozens of different styles and sizes of these parts and dedicated fixturing is about the only way i see to make it happen. Concrete is cheap and easy to make so one fixture for each different family of parts shouldnt be to much $. And quickqrete would dry and set in about as much or less time than we could make a dedicated fixture.

So has anyone here tried using concrete before? Im sure its not a new thing but ive never seen it done around here. Do you think bolting or clamping say a 2" thick pad of concrete to the table would hold up to the vibrations of machining and to the compression of clamping a part down onto it.

Somebody tell me im not crazy.