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 at the interface. It also reduces the bending load on the knob mechanism, which was never meant to see such a cantilever load.

I should note that this handle isn't as terribly short as it seems. The default length (the black print photo) is about 20% shorter than a typical lockset length (the gray print photo), but it seems grossly short compared to other printable concepts because it appears most everyone else ignores the radius of the existing knob, resulting in an abnormally long assembly. It's not a suitcase handle. You don't need extra room to monkey-grip the lever. Even a 75mm handle is long enough to open with your knee or butt (or elbow if you're a hobbit).

There are two main files included: a smoothed approximation, and the original square-edged version it's based on. Use whichever you prefer. I'm including a handful of example STL files, though it's unlikely that any of them will be the right size for you. There's also an extra SCAD file for generating test rings for double-checking fitment.

See the original SCAD file header for notes about printing and assembly.