Pressure calculation

[hexalobe]

Hello,
I'm trying to calculate the amount of pressure required for rotary broaching. I've found a few charts online, and we can see what the machine is telling us the pressure is, but I'm looking for a formula for calculating thrust lbs. in different materials, using a 1/4" hex for example. The pilot hole is already drilled, so the calculation is just for cutting the corners out of the hex hole.
Thanks!

 

[BillPSU]

The minimum broach force for a round hole is calculated

Force = 3.1416 x hole dia before broaching x number of teeth engaged x rise per tooth / 2 x constant

Constant is based on material in psi

Aluminum 200,000 - 300,000
Brass 200,000 - 300,000
Bronze 350,000
Cast Iron 200,000 - 350,000
High Temp alloy steel Up to 600,000
Lead 60,000
Mild Steel 450,000
Steel Casting 400,000

This calculation does not take into account other factors such as cutting fluid, chip breakers, hook/face angle, sharpness.

 

[hexalobe]

Looks great, thanks for your help!