Cutter head loads....anyone?...anyone?

I'm interested in determining nominal milling cutter loads. Because
I've changed my design from steppers to servos, I want to make sure
I'm able to generate the required forces at the cutter head. While
I'm building a 3-axis machine primarily to cut PVC and wood, I'd like
to have the option of replacing the router with a spindle, allowing
me to cut metals. I'm willing to accept slow, even minimal, feed
rates.

Question: What are typical axial loads for slow to average speed
mill/drill operations?

Many thanks,
Ron