Knob for 3/8"-20 UNC camera mount bolt

thingiverse

Warning: requires lathe work to create a metal washer that is 2mm thick overall, has a 9.5mm central hole, and a stepped external diameter. One step diameter measures 19mm by 1mm thick, while the other is 21mm by 1mm thick. A standard 3/8"-16 UNC bolt is used on larger cameras and telescopes, whereas the ordinary camera bolt (Canon, Nikon, etc.) is a smaller 1/4"-20 UNC. Camera knobs, even a cheap Desmond D-ring, cost $6 or more. However, this particular knob, designed for a telescope, costs no more than $0.50 in materials. I aimed to embed a bolt into the print but compromised by capturing a metal washer instead. The knob is printed with the "washer-side" facing the print plate. A steel or aluminium washer is inserted just after the recess is printed, ensuring it sits flush with the bottom of the knob. Before inserting the washer, ensure that hair-spray has been applied to its surface, or the plastic extrusion laid on top will not stick to the washer! Additionally, pre-heat the washer by placing it on the heated bed before insertion. The washer cannot fall out due to its stepped edge (although this feature is not essential). In practice, the plastic knob only exerts force onto the bolt sides. Once tightened, clamping forces are 100% metal-to-metal (which is why a metal washer was used). My objective was to ensure that zero 3D printed plastic parts were crushed when tightening equipment using this knob. I have not yet pushed the tight-fit plastic cap home as I still need to machine the bolt shorter and create a slot for a retaining washer. I will likely epoxy on the cap, then sand it flush and paint. Form Futura ABS pro sands down exceptionally smooth.