Hello Bill and welcome to the forum.
I see that you already have a couple of responses on the lathe size and tool post questions.
Let me start some dialog on cutting tools. This is a really big field. I am sure some of the other members will jump in to add some more or make corrections if they think I am steering you wrong.
I hope I am not being too rudimentary here - I am trying to base the response on what I am reading into your question.
As I see it, cutting tools (these days) come in 3 flavors:
- Traditional high speed steel (HSS)
- Brazed carbide cutters
- Index-able carbide cutters (with replaceable inserts)
HSS cutters can be had "pre-ground" or you can buy blanks and grind them yourself. HSS tooling can be a little more messing around than the carbide route, but I think that all the professionals will quickly point out that there are things you can do with HSS that is difficult to get with carbide. Not only can the HSS get you complex cutting surfaces, but it can also give surface finish improvements over carbides. Let me stop there with HSS and let others add to this.
Brazed Carbide Cutters were new on the market when I was first exposed to machining. (Tungsten carbide is usually just called "carbide" amongst machining circles). This is a small piece of carbide brazed to the end of a steel tool shank. To the tool holder, it looks like a piece of HSS. Carbide holds an edge much longer than HSS. Carbide can usually be run at much higher surface speeds than HSS. The hardness that makes carbide hold an edge also makes it subject to fracturing. It is possible to break the corner off a brand new brazed carbide cutter just by bumping it into a steel, non turning part such as a chuck or tool post. The brazed version can be re-ground (with the proper grinding wheel) until there is almost no carbide left on the shaft. The brazed cutter can also be ground to get profiling shapes not available "out of the box." Carbides come in several variations of hardness / toughness depending on the application. For example, turning with an uninterrupted cut usually requires a tough rather than a hard carbide. I'll leave it to others to go into more details here.
Index-able Carbide Cutters have a replaceable carbide "insert" in place of the brazed-on version. Furthermore, the carbide can be "indexed" one or more times to expose a new cutting edge as one becomes worn or damaged. The carbide insert is either screwed or clamped into position. The "holder" is reused indefinitely as inserts are replaced. Index-able cutters come in many shapes and sizes with many types of chip breakers for different applications. Some can be indexed as many as eight times before they are replaced. Each carbide shape requires a different holder. Holders for the same shape are also furnished in RH, LH and several other versions.
You mentioned thread cutting. This can be done with any of the above three types of cutters. All can be purchased with the necessary angles already ground into the tool. Or, with HSS, you can take a blank and grind your own (I have never been good at this - I like to buy preground thread cutters). The most common USA threads use a 60 degree angle cutter. But, there are other threads that use different geometries.
I recommend getting a hold of "Machinerys Handbook." It goes into great depth on cutting tools, thread geometries and a thousand other topics important to machining. You can find used copies on EBay. Amazon sells new copies. It seems that the used versions are not that much cheaper than a new one. There is enough reading in there to put you to sleep for many nights.
Terry S.
