helix axis for non regular helices

 Some time ago someone asked for routines that calculate the helix axis in the
 case of non regular/bended helices. However, I have lost his mail address.
 I'm also interested in founding out if such routines are available.
 I' will appreciate if someone can send me some informations and/or
 references about it.
 You can anwer to me directly  (paterlin "at@at" msvax.mssm.edu)