Robust Parametric Doorknob Levers (SCAD)

Unlike other printable doorknob levers, these must be sized to fit to the knob and glued in place permanently. The method of attachment does not leave the printed part under constant mechanical stress; consequently, it's less susceptible to creep deformation or cracking due to exposure. It also means that there are no screw holes, counterbores, or flexure slots to weaken the structure (or fill with insects), and it wastes none of the available material strength merely to effect a meager friction force.

The torque load isn't the main problem. It's the load applied when pushing and pulling the door -- especially entrance doors with tight weatherstripping and a habit of accumulating ice. Keep those loads close to the spindle, instead of treating the assembly as if it were originally designed to be a lever. A shorter handle and large hook encourage a normal inboard grip (thumb over the knob), instead of a grip solely on the lever. This reduces the bending load on the lever and shear