In addition to what Jerry mentioned, there was recently a thread here started by Bob Pastor. he gave a bunch of info on some indexable hss tooling and that may be of interest to you.
When you're trying to find the sweet spot in the angles, don't forget that just as important as the side of the tool, the tool height is a big piece of the pie. If you can sorta visualize the insert as it cuts, remember that for specialty cuts, there may be a different angle on the front of the insert (tool) as there is on the side. Feed rate that is light might require a itty bitty bit less angle than if you are feeding at a "proper" rate. Much of what we do in gunsmithing is at speeds and feeds way below ideal for the tool. So, angles have to be changed accordingly.
The height of the tool effectively alters the angle. Visualize the end side of a round in the chuck and you're getting ready to reduce the diameter. If you raise the tool, you need to increase the tool relief angle to allow the tool to cut. Makes sense since the part is round and as we move up, the point has to be extended more. There will be a sweet spot where you achieve the finish you want, and that might depend some on the machine. I'd say that the more sloppy the machine, the less likely you are to get away with good results when you raise the tool way above center. At some point, the tool might begin to pull itself in and that's generally not desirable. I think a lot of times, people will put too much angle on the left side of the tool because they made it equal to the front, and with a slow feed and a not so solid carriage, that's not a great idea.
Nothing said here is going to really solve things to where you get perfect results. Finding that spot is something you just have to try by grinding. As Jerry said, using the approximate angles used by commercial insert companies is a great place to start. And, if you go take a look at some of the websites, they will give you detailed drawing of the inserts that will really help you get your head around the angles. Start there, and don't get too far from their example, even though, your feeds/speeds are no where near what production stuff runs.
Most of all, find a way to put a nice radius on all your tools, and make sure the angles are kept intact when you do. On fine stuff, I put them on by hand with a stone cause I simply can't make .003 radii on a wheel. Remember when you cut, you're supposed to bury the radius. So, if you want to make decent looking cuts and not take a lot of material each pass, then ideally the radius needs to be smaller. I've got one particular boring bar I like to use for small work and I've got .003 and .007 radius tools for in it. There's a noticeable difference between the two when doing fine, slow work.
Last but not least, use the feed lever any time it's possible. I know it's not on the compound, but, think about it, if you don't maintain a consistent speed, then the tool angle is effectively changing every revolution, and it's no wonder a part looks ugly.
