I've never used a collimator, only a piece of stiff plastic with frosted tape on the lens side. It's cut to the dimension of a 6x9 negative, plus a little on the length, so I can be sure it will sit in the proper place (and BTW, the film and paper are so close to the same width, a stepped plane can't be for film in the lower and paper in the upper; rather, it's to keep the pressure plate from making scratches in the film by insuring a fixed amount of space). I use a loupe (or the back element from a triplet) to examine the image and establish critical focus on an object *at least* a quarter mile away, preferably a mile or more.
The cameras I've reset this way have produced some of the best images I have (including my Wirgin Auta, Kodak Reflex II, and Argoflex EF).
The ring vs. lens barrel varies from camera to camera. My Wirgin has four starts, and only ONE of them will allow setting the focus correctly and mounting the name and focus scale correctly as well. What I found worked well with this camera was to set the focus, test the fit of the rings, and if it wasn't right, back the front element off carefully, while pushing it *on*, until it "clicked", then screwing it back in, and going again. This allowed me to proceed sequentially around each of the four starts until I found the one that allowed the correct scale and name ring installation with the focus correct.
Other cameras are easier on this; the Reflex II and Argoflex both have "infinitely adjustable" settings, so it doesn't matter which start you get the lens on when reassembling.