The nose radius typically dictates the minimum depth of cut, something like 1/2 the nose radius. There are many factors, also the type of insert, rake, molded vs. ground, etc.
Even among experienced machinists, choosing the right insert for boring a hole remains a difficult process that is fraught with myth and misconception. However, it is no myth that insert selection can completely save or kill performance on an application.
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You will find that something like a CCMT 32.51 is a good all around and durable insert for metal removal, if you want a better surface finish then go to a 32.52 and increase the feed. The feed rate is typically 1/2 the nose radius, but may be slower which may or may not improve surface finish. So for a 32.51 a feed of something around 0.008' (nose radius is 0.016"). Go too slow and you will push the material and not cut it. Metals like stainless 300 series and steel like 4140 require higher reguire higher feeds (and adequate depth of cut) otherwise they work hardened. Also increase the feed rate to break the chips. If you want to cut a very small depth, then I would switch to a sharper ground positive rake edge, (like a CCGT) as is often used for aluminum. You can get very fine shavings, almost like steel wool. But you are much better off taking the last 2 or 3 cuts at something like 0.005-0.08" and measuring the actual cut vs. expected and compensating for the difference. Going to a larger nose radius will give a smoother finish, but applies more force on the cutting edge which can cause chatter in a less rigid setup, also you need to increase the feed rate.
HSS, it is probably how it is ground and the nose radius/geometry. I do not use it because of the convenience of using the inserts, they last a long time, and they are quick to switch out for different materials without changing the cutting position. I can purchase a box of the Iscar CCMT32.51 IC907, a great all around grade for $30-40, and they can last me 2 years. Korloy polished carbide CCGT inserts for aluminum. I have some Kennametal inserts that I picked up for more exotic materials, but haven't had to use them. I find on boring bars that I do better with something like a CCGT 32.52 insert, I seem to get less chatter even though the nose is bigger. Probably the sharper edge decreases some of the cutting pressure. I also use a CPGT 32.51 insert in my positive rake boring bars. This decreases the cutting force, but the geometry make the insert edge more fragile. Worth reading up and experimenting, I am always learning new information and seeing what works.
