feed and speed formula for glass

Hi all,
new here on the forums. i searched through the forums for speeds and feeds for milling glass. i am looking for a formula to figure out the opitmal numbers. seems most people just work it out by feel and expericence. i am not new to cutting glass but i was recently watching a youtube video with a guy from Iscar tools and he is a wealth of knowledge on metals. i was inspired to try and get more technical knowledge about the SFM, feeds and speeds in milling glass, seems there is not much out there.