Raising this thread from the dead, I have revived and edited the Spool Thread Co. formula document. I am sharing it because the link in the first post is dead.
If you have any comments or other feedback, feel free to comment on the google doc, reply here, or PM me.
Also, the Airetic String School page is gone, but the Airetic Strings youtube videos for making string without a rig and making string with a rig are still accessible.