Does Counterbalancing Weight Differ From Concrete Weight in a Spinning Mould?

[lwasmund]

I am forming a concrete utility pole centripetaly in the mould (lathe). I need to have it form with an aperature(box shaped hole). I need to place a box to form the hole for the aperature and it needs to be of proper weight. the weight the concrete would of been had there been no aperture. It is best if i place the box in without it being of the desired weight, and counter balance it on the outside of the mould. My question is would the wieght needed to counterbalance the pole when spinning need to be different then the aproximated weight of the concrete(403lbs). Since the weight is on the outside of the mould?

thanks

 

[lwasmund]

I understand a little about physics. My main study is civil eng. I am looking for the factor that I can add to my equation to calculate for the difference with the counterbalance being on the outside. think of a ball on a string. except no the ball isn't on a string but held in orbit by the perimeter. How much mass/weight do I need to counterbalance. When it is to counter 403lbs of misplaced concrete.