I used to grip the cue with only my thumb and forefinger touching the cue. I have been trying to change it to where all of my fingers are on the cue. Since doing this I have noticed that towards the end of my backswing the friction from my pinky sliding up the cue causes it to rotate a little. And when my cue comes forward it reverses rotational direction. Is this normal.
KingJerryO:
The action you describe is called "corkscrew" and is the natural result of your fingers opening and closing during the grip's transition through the stroke. Earl Strickland has a bit of a corkscrew motion via his wrist turn at the end of his stroke (but it happens *after* contact with the cue ball).
It can be both a good thing and a bad thing. If you can keep the corkscrew straight in-line with the cue's direction of travel (e.g. sort of like the way the "lands and grooves" of a rifle's barrel imparts desired spin on the bullet), but without wobble or yaw, there's no consequence to it.
However, any action imparted to the cue besides just straight back and forth motion, is UNNECESSARY motion, and is something "extra" that can break.
If you look at the architecture of your hand (hand placed in front of you as if you were a traffic cop issuing the "stop" signal), you'll see that all of your fingers are of different lengths -- your middle finger is the longest; your index and ring fingers are approximately equal in length; and the pinky is the obvious shortest finger. You'll want to adopt a grip that compensates for the different lengths of the finger. Most instructors will advocate either a two- or three-finger grip (we're talking just the fingers here, not the thumb -- we're taking the thumb for granted). "Two-finger grip" would be the thumb, index, and middle fingers. "Three-finger" grip would be the thumb, index, middle, and ring fingers. Very rarely will you see all fingers being used. (A notable exception would be Jim Rempe -- and the corkscrewing of his cue is readily visible.)
Personally, I use a two-finger grip. Once in a while, I'll use a snooker grip, which uses the rear fingers of the hand, and the index finger is loose, pointing somewhat straight down. A good example of this "rear-fingered grip" can be seen used by Ronnie O'Sullivan:
http://youtube.com/watch?v=W2Ye61WiLMk#t=485
In either case (front-fingered or rear-fingered grips), not all the fingers are used in the grip. There's a reason -- because the cue surfaces itself do not change, you want the hand, instead, to adapt ("give") throughout the stroke.
Hope this is helpful!
-Sean