I use sandpaper on a file to shape my tips by only sanding downward.
I do not like to do it on the lathe because it will, in my opinion, cause the fibre to go up on one side, and down on the other, on my tip. I want all the fibre to go downward, as it is the direction the pressure will be applied when the cue ball is striked.
Even when I trim the tip on the lathe, I always only go downward with my blade.
I tape the layers on the tip that I do not want to take off, and the ferrule as well, since sometimes the sand paper seems to leave traces of scratch marks on the ferrule, especially soft ferrules such as Predator's.
I do not use any of the tip tool, I do not know why anyone would want to generate an unnecessary amount of heat to one's layered tip, and mess up all the fibre on the surface of the tip, by spinning the tip like an ancient man would when he tries to generate fire.
Anyway, I think in order to provide the most contact surface area, the radius should be the same as the radius of the cue ball. So, it depends on what game you play, 3 cushion, snooker, or 9 ball...because the cue balls used in these games are different.
I like to leave the top relatively flat, but the side shaped to the radius of the cue ball. I will tap the side of the tip, in order to push the fibre inwards, rather than the top, which would push the fibre outward. Then I will just leave it. The tip will be shaped from my shot selection as I play with it.
The only thing I do to it after a while is to trim off the mushroom if it occurs.
I have never compared my tip to the shape either a nickel or dime because in my opinion, those shapes were not designed for billiard tips comparasion; they are shapes of coins we use on a daily basis. I think it would make more sense to compare the shape of a billiard tip to that of a cue ball.
That is my opinion on this matter.
Richard