The faceplate in Night Gryphon's Logitech c270 webcam manual focus adjust ring is perfect, but the lenses on newer C270s have a slightly smaller diameter than old ones. As a result, the focus ring doesn't fit.

I adjusted the inside diameter of the focus ring to grip the lens, and changed the ring to have a smaller diameter and protrude from the camera (so that the screws aren't covered). I also tightened the fit of the ring in the faceplate.

I've made two rings with depths of 6mm and 8mm. I printed the 6mm and it works, but I think the 8mm will be easier to grasp.

You'll need to get the faceplate from Night Gryphon's thing, and follow the standard instructions for removing the glue that holds the C270's lens in place.