I bought some of the foam from one of the knife making supply web sights and made a press. the amount of spring retention can be controlled and adjusted later if necessary.
another thing I found out the hard way is to NOT EVER use a belt sander or sand paper on the Kydex, unless you can scrub the inside of the sheath/holster. if you get one tiny grain of sand in there, it will scratch the knife every time you use it and it will never go away. I use files or rasps for final shaping.
