Ergonomic Door Knob Lever, Fully Parametric

thingiverse

This adapter converts a round door knob to a door handle with a lever, inspired by the design of tbirdrv. I reimagined this concept from scratch in OpenSCAD to let dimensions be fully customized for various door knob sizes with a precise fit, ensuring that parts align seamlessly. I'm passionate about creating smooth ergonomic 3D printed parts, so this design calculates a curved hand-friendly structure with rounded edges that are both comfortable and visually appealing. This results in additional calculation time for OpenSCAD to render the final result, but the wait is worth it. If you lower the sfn parameter to 0, rendering will be quick for adjusting dimensions, but I recommend raising it back to 4 for a smooth finish. The most stunning appearance comes from matching the nom_knob_diam variable in the .scad file within at least 0.3mm of your door knob's correct diameter. Calipers and precise calibration are essential for this; otherwise, you may need to adjust and reprint. You can also try terminating a test print early and using the first few layers to check your measurement. When perfectly sized, the nut and bolt sides will clamp together tightly as it reaches the desired grip on the door knob. The example stl file is designed for a 54.8mm diameter door knob, held in place with an M5x12 bolt and an M5 nut. Note that the OpenSCAD file uses my threading library to create properly sized recessed bolt and nut holes - check it out here: http://www.thingiverse.com/thing:1686322. Installation tip: If your print is slightly wider than needed, or you want to increase grip on the door knob, try stretching a thin strip of standard poster putty around the knob before mounting the lever. This will significantly boost the coefficient of friction between the two surfaces in a removable way, providing a sturdy hold without needing excessive tightening. Print Settings: Printer: HICTOP 3DP-11 Resolution: 0.5 x/y, 0.2 z, 1.5 perimeter, 1.0 top/bottom Infill: 50%-100% Notes: Using solid infill can add strength for handling the leverage applied to this part when installed on a door. If you use PLA and print slightly low in temperature, increase your temperature at least to 210C to avoid delamination under normal strains. The design is symmetric, so left and right side door knobs work with the same stl file. Slightly better aesthetics are obtained by orienting the design so that the printed side faces toward the door.