Figure #2 shows the decreasing stepper torque as speed / PPS is increased. Added to the motor curve is the RPM and IPM when threading for a ¼ - 20 thread. The graph is for the Z axis. Won’t know how much torque will actually be required until after installing and adjustment of the ballscrews are done. At least it’s obvious that with the back gears engaged, there will be enough motor torque to do the threading. Note that in using the SmoothStepper , velocity increases of 2X and greater were achieved on my other machines so speed is will be increased relative to the torque. Also not that the motor curve is for a lower voltage than what will actually be supplied to the motor. Even though you have a motor curve, if the curve is not truly representative of your actual drive, current and voltage and wiring configuration, you can only use it as a guide for anticipated performance. Knowledge from past experience really helps!
RICH