The experiences whether hammering or pulling to remove shaft/gear box/ bearing seeks high attention from the maintenance people. There is no specific Engineering theory for this. The practical experiences/methods and environment will suggest what to do and how to do. So don't panic. Before doing such types of work/job try to look for every possibility to pull out the shaft/gear box/ bearing rather to hammering. The hammering will cause a great damage/loss in the long run. Sometimes it needs some arrangement to pull out the object with the on hand Puller and it may take time. From my practical experiences i like to share an incident happened in my workplace. The technician tries to take out a Gear box which was coupled in a solid shaft with key way. They tried for a long time , but unfortunately they were failed to take out gear box. As the gear box body didn't well suited for pull out the gear box, technicians were engaged in hammering behind from the gear box. Another things were the gear box was in top vertical position and there were little space for maintenance work. However at last decision were made to take out the gear box by pulling . So they made arrangement with the on hand puller and finally they succeed to took out gear box. I like to draw attention of maintenance people to share such kind of experiences .