i want to mill a connecting rod out of 1/4 plate alum to start so lets say I have a piece of plate 4 inches wide 10 inches long a mount that in the mill do I need a hole in the center of the connecting rod to hold it to the machine or what happens when it is cut out.

Usually the two holes at either end of the con rod are cnc drilled/milled and these are used to secure it to a sacrifical plate (wood perhaps) then it is profile cut.

Hope this helps.

Tweakie.