I've got an old Bosch corded hammer drill, model PSB 500. It's not the "RE" (reversible) model. The chuck is a traditional one with the jaws and the key to loosen and tighten the bits.
Since this model is not a reversible one, the chuck has not the central screw to remove. There is only a sort of flat head, it seems like a pin, and a really small hole on a side of this flat head. I can't understand if the hole has something to do with the removal process.
I followed the procedure I found here and on YouTube to unscrew the chuck: - lock a big Allen key in the chuck - hit it with a hammer in counterclockwise but: 1) the drill model doesn't have a lock button to avoid the rotation of the entire engine group; 2) the chuck shaft doesn't have a wrench friendly grip (the notches you see in the picture are at 120 degrees so useless for a normal wrench); 3) I tried to lock the shaft with a pliers but the chuck doesn't loosen the same.
Is there a way to remove this kind of chuck?