Yep, title says it all. The last few days, instead of doing any drills, I've just been setting up shots that are giving me trouble and working on those for a few hours, mainly cut shots into the side pockets and thin cut shots into the corner pockets with the object ball just slightly off the rail. I've made a lot of progress in the first but very little in the second.

I know if the ball is frozen on the rail, I put English on whichever side the pocket is on and aim to miss the object ball by a hair. But when it's slightly off the rail, I consistently undercut it. I'm able to make the shot if the object ball is one diamond away from the pocket but if it's further than that, it usually contacts the side rail before going into the pocket. Sometimes, I'd over adjust and I'll end up sending the cueball into the rail first then into the back of the object ball, kicking it somewhere not even close to the pocket.

I've set up ghost ball shots in which I freeze another ball right up against the ball I want to pot and I'll hit the ghost ball head on. The object ball always goes in and I could pound the ghost ball at almost break strength and the object ball will still pot. But when I try to visualize where the ghost ball would be, I'd end up undercutting again.

The silver lining in all this is my cut shots with more angle to work with and/or with the object balls further off the rail is getting way better. But how do I improve on thin cuts off the rail?

Frank, I use the ghost ball technique on almost all of my shots. Just keep practicing that and you'll eventually be able to hit the spot consistently without using another ball to line it up. Rail shots like this, IMO, are one of the harder ones to get consistent on even though lining up the angle is no different than other shots. It's mainly because you have less wiggle room to get the object ball into the pocket.

Have you always had this issue or is it something that just happened? If it just started, our mechanics are off. If you've always had trouble, start with easier cuts and practice them progressively more difficult.

I used to have the same issue, but I can't remember a simple fix.

Always had the issue. Decided to do something about it.

You'll get some contact-induced throw on this type of shot, and given the small margin of error, that's usually enough to create an undercut miss.

Since it's pretty challenging to adjust your aim correctly because you'll feel like you might miss the ball completely, the easiest fix is to apply some outside English if it's a "standard" shot and there's not too much distance or velocity involved. Otherwise you might have to correct your aim some, if you want to use this technique (see "squirt").

Note that you will be using inside English when the ball is frozen to the rail, if you like the "miss it intentionally" approach. You could also try NOT missing it intentionally and using outside English just like I described above, since that approach works also even if the ball is completely frozen. All this might be a bit confusing at first. But I'm sure you'll get the idea.

The trick here isntommove both the cue ball and the object ball about two inches into the middle of the table and then shoot that shot. See, here's the thing, the actual shot you're playing is no different here than from the original position -- the angle is the same. The only reason people tend to miss when the ball is a little closer to the rail is because it's a little harder to see and because they get intimidated. Don't be that guy.

The direct angle is the same but there's less room for error. You don't need to be quite as exact when the shot is off the rail because you can cheat the pocket. That luxury isn't available on rail shots. I, personally, would just keep the ball at the rail to practice it.

Disagree. Shoot it ten times from the easier position, then ten times from the rail. Rinse and repeat. By the third rotation you should make all 20 without missing any.

As with about everything in pool practice will solve your problem in the end.

Have you tried CJ Wiley's Touch of Inside technique? I was messing around with it yesterday and it seemed to really improve my thin cuts.
http://www.cjwileybilliards.com/
Try the day pass for 5 bucks and mess around with it. I was very impressed with my results and look forward to practicing more with it.