Wild guess, if you use the app I do to calculate how many layers of tape you need on a wedge to get an 18 degree angle on the bevel my guess it would also work with a worn down spine on a full hollow. It takes into account how wide the spine is and what size the blade is to get you into the ballpark of an 18 degree bevel which is , from what I have been able to gather, is the bevel angle spec for a brand new razor with the proper geometry.

Bob