Here is a rapid fire medley of several players rotating the double bend into the ball.
In the first frame of each sequence, the butt cap of the racket points at the ball.
The butt cap of the racket must point towards the net/ball so that after rotation,
everything is lined up properly on contact.
Focus your eyes on the shoulder line/torso of these players. Watch how the shoulder line/torso
rotates into contact. Notice as well how the elbow angle never changes during this rotation.
If you snap or move at the elbow joint (which most people do), you lose the mass of the double
bend structure coming into the ball as a unit.