Answers to Lewm and timeltel questions are HERE. Be SURE to download attachment at bottom of page.
There is no centripetal force vector that consistently aims toward the spindle. It has been a long time since I read Kogen, but if he claimed the existence of centripetal force in skating then he either was referring to a condition similar to the one in my first slide of the download (depiction of the treadmill), which is a minor component of skating force, or he used the term in a figurative sense, not literal.
The profile of the very tip of the stylus will have no impact on the force vector directionality but may have an impact on coefficient of friction.
By the way, Wally passed away in 2018. This is J.R. Boisclair. I did not use my name as my moniker not because I am "hiding" but because I felt I should make it clear that I have a direct interest in this industry and it would be best if you knew who was doing the posting. Most people know WallyTools and fewer know my name. Cheers!