For most learning to go from a high Z rim delay to a center delay marks a whole new level of understanding in disc control. It means being able to bring most any angle throw back to the center, increased center control, and leads to understanding angle changes and off center tips. For me this skill took some practice.
To accomplish this task it helps to be able to throw a high Z steep angle to your self. To learn clock right hand throw a right handed backhand throw with tons of spin. It should come off on a steep angle, nearly perpendicular to the ground such that the bottom is pointing more downward than the top and the nose is pointing to the right. It should also be perpendicular to your chest plane. Now that the disc is in the air use your right hand and take it on a rim delay. Your palm will be facing to your left and your finger(s) should be curled under the rim. Let the disc hang in this position long enough to get it under control but not so long that it tilts around so the nose is pointing to your body. From here there are two common methods of getting to the center.
1: Give the disc an upward tug. As it lifts up hold your hand still so that the bottom of the disc rides along your finger nail(s). Once your nail is near center push hard to the left. The ideal location is it about 6 o’clock halfway between the rim and the center. As you push to the left the disc will flatten out. Once it is flat get the center delay under control.
2: Gently swing the disc forward. As the disc swings forward the rim will pull against your nail forcing the disc to level off. Once it is halfway flat move your nail to the center and gain delay control.
To learn counter left reverse the right/left directions as if looking in the mirror.
Once you become proficient at this maneuver try it on a different angle or the opposite hand. Example, once the disc is on a rim delay let it drift around on your nail until the nose is pointing upwards to the left perpendicular to your chest plane. The motions are the same. Give it a tug so it rides up your nail. Now push right at 12 o’clock between the rim and the center. It will flatten out as before. Note: you may have to duck your forearm below it to keep from knocking it off your finger.
The biggest thing to learn is that the location to press in with changes based on the direction of the nose. It’s always 90 degrees ahead of the spin from the nose. So, with clock spin, if the nose is pointing away from you (12 o’clock) push it out so the disc rides up your nail, then push towards you at 3 o’clock. With counter spin you’d push at 9 o’clock.
Once this becomes second nature try flattening the disc directly from the throw with a tip. The physics are the same. Just tip it up 90 degrees ahead of the spin from the nose. You can also try to flatten it out from a rim delay to a flat set. This set it the beginning to many moves and catches such as a scarecrow and a one and a half btb.