The original focusing knob of the Plaubel PL69 is a 18 mm diameter knurled turning knob. The knob is attached to an axis which holds a cog wheel that matches with the toothed rack on the monorail of the camera. Two springs apply some force to the wheel rack system, so the friction guaranties little backlash when the dovetail with the standards moves along the rail.
For me the knob is somewhat small and a first idea was to change it to a geared knob with the possibility of somewhat finer focusing adjustment. I bought a prefab geared know which I attached to the axis on the opposite site of the standard knob. This was mainly because I could not manage to get the original knob off the axis, which I did not want to damage. A small brazen hull and an aluminum plate had to be made to connect the knob.
In principle the new know worked fine and the focus adjustment was in general more precise. However, at some places along the monorail, some increased friction was too much to be handled by the geared knob. Actually in the knob the friction between two plastic gears handle the rotation of the axis. This delicate connection was not strong enough to move the front standard of the camera smoothly along the complete rail due to overrunning.
In consequence, I removed the geared knob and made a new larger knob which is basically an aluminum ring which tightly fits on the original camera knob, secured by three set screws. First, due to its 30 mm diameter producing a higher torsional moment, and second due to two attached brazen handles, the new knob gives a much better feeling when focusing.
