some_angle += 5 *time_step;
ent_animate(me,null,0,0);
ent_bonerotate(me,"bone2", vector(0,0,some_angle)); //pan/tilt/roll so in this case you changing bone's roll but you want change bone's pan

So You should play with vector(some_angle, some_angle, some_angle) to check which one rotates your bone aroud axis you want to?