Can someone tell me how I can stop flipping my hands at or before impact?
Stop using them. Your hands are over active.
Only the left half of the Flying Wedge moves vertically to uncock- and on the swing plane. The right wrist remains bent at impact. Drive the hands to an AIMING POINT past the ball and there is no need to flip them. Maintain Lag beyond ball poistion.
On another thread there was talk about the hands remaining "frozen." Frozen is just keeping the Flying Wedges intact and OPERATING correctly. Left -cock and uncock and the right -bent and motionless. Frozen does not mean stiff, static or rigid. Frozen means NOT wobbly.