Yes , that is right .. What is the tool that a repair guy uses to fix that gap..?
The thing is that from your description alone, it's hard to tell exactly what the problem is. Here are a few possibilities, each of which would require different tools:
1. There could be a very small amount of space between the hinge tubes and the rod and/or small gaps at the ends of the hinge tubes, in which case a set of swedging tools could help. However, this should not lead to several mm's of movement.
2. There could be a small amount of extra space in the post hole, allowing the entire rod to move around, in which case a post-fitting tool might help. Again, this should not lead to several mm's of movement.
3. The original rod may have been replaced in the past by an undersized rod, in which case the problems described in (1) and (2) would be fairly severe and probably not addressable using swedging tools and/or post-fitting tools alone.
The amount of movement you report and the fact that you indicate that shellac may have been used in the past to ameliorate the problem suggests that you're probably in a situation close to (3), either because the rod is the wrong size or because the hinges/post have suffered from severe wear. If this is true, then the problem won't be easily addressed at home, unless you have a lathe, some brass and/or rod stock, and some soldering skills.