Shaft Design Calculator

def shaft_diameter(T, M, tau_allow, Kb=1.5, Kt=1.0):
    """
    Minimum solid shaft diameter under combined bending + torsion
    (ASME maximum shear stress theory).

    T, M      : N·mm
    tau_allow : MPa
    Returns   : diameter in mm
    """
    import math
    if tau_allow <= 0 or Kb <= 0 or Kt <= 0:
        raise ValueError("Invalid parameters")
    equivalent = math.sqrt((Kb * M)**2 + (Kt * T)**2)
    d_cubed = (16 / (math.pi * tau_allow)) * equivalent
    return d_cubed ** (1/3)


# Example
T = 350000      # N·mm
M = 180000
tau = 72.0
Kb = 1.5
Kt = 1.0

d = shaft_diameter(T, M, tau, Kb, Kt)
print(f"Required diameter: {d:.2f} mm")

function d = shaft_diameter(T, M, tau_allow, Kb, Kt)
    % Minimum solid shaft diameter (ASME max. shear stress)
    % T, M in N·mm, tau_allow in MPa → d in mm

    if nargin < 4, Kb = 1.5; end
    if nargin < 5, Kt = 1.0; end

    equivalent = sqrt((Kb*M)^2 + (Kt*T)^2);
    d_cubed = (16 / (pi * tau_allow)) * equivalent;
    d = d_cubed^(1/3);
end

% Example
T = 350000;
M = 180000;
tau = 72.0;
d = shaft_diameter(T, M, tau, 1.5, 1.0);
fprintf('Required diameter: %.2f mm\n', d);