Setting focus at near distance is the wrong end to do it at. Check and set it at infinity.
The focusing ring should be an empty tube with three screws to fix it in position, so put a ground glass at the film plane, focus at infinity and once you achieve that, set the focusing ring.

The score mark should be aligned with the edge to it's left in the picture. That's the infinity stop and the focus ring may have a machined section that gives a "hard stop" at infinity.The fact that it's there says someone has been into the lens before, they don't come from the factory that way.

The helical threads are called "interrupted threads" and they have as many start points as grooves. If, the focus is off by a significant amount, it's likely been assembled one thread off. If it's close enough, and works, leave it be, but at close distance it may just unscrew again.