As with anything, quality tooling makes the job easier. One thing I've come to lean on over the years is insert choice. My tool package for barrel work is tailored towards inserts intended for "hard turning". Simply to mean the edge prep on the insert is sharper than one that's going to be used for production threading on softer materials.
The reason is I'm not spitting out thousands of parts pert shift. I'm fitting the thread to a receiver or a thread gauge. Trying to do this a .001" at a time when chasing down a pitch diameter is harder to do with the wrong insert. The one's for production work lack a sharp edge. They rely on tool pressure and consistent material. A sharp edge erodes faster where's one with a healthy radius on the cutting surfaces lasts longer. These inserts are designed to heat the material and make it go into a plastic like state. You see this immediately in the chip formation. It'll come off the tool a lot hotter than a "sharp" tool.
-One thing I avoid in barrel work is a full profile insert that dresses the entire thread profile (thread crest). Once the insert gets to depth, that's it. I have no control or say in what my OD is vs the pitch diameter. A partial profile insert doesn't do that.
When you install a variety of barrels made to different heat treat specifications and different lots of steel, the way the tool behaves when cutting will vary. A "sharper" tool designed for hard turning will have an edge that cuts with less tool pressure. This means its less likely to work harden the surface when trying to squeal that last .001" or .002" from the pitch diameter. Its because these types of inserts are intentionally designed to "get in, get it done, then get out". You don't try to finish with these on a .001" pass. You might do a 16 pitch thread in as little as 4 passes. The setup when writing the program here is the ticket. You take into things like tool rigidity, work holding, Surface Footage, Depth of Cut, material type, and the need to get a cycle time down to where the job is profitable.
What your paying for when hanging a barrel is someone's time to stand there and fit the two parts elegantly. That commands a different choice in tooling.
What often happens with production minded tooling when trying to fit something is that it'll work harden a candy shell on the surface of your part. You keep picking at it trying to get that last bit, then it suddenly gets under the "skin" and rips .005" (or whatever, more than you want...) from the material. Now your thread is like hot dog in hallway.
It does this regardless of whether you have an old chunk o matic manual machine or the latest, greatest cnc that's built like a brick shit house. Machine rigidity plays into it considerably, but the tool package has to be right to start. With a clunky old lathe, it's even more relevant. This is why guys who grind their own tooling from HSS often have better results (assuming they can grind a tool properly). The tool pressure goes way down because the edge prep either doesn't have a radius or its very, very small. The issue here is getting it right every time and keeping up with the maintenance. HSS wears a great deal faster than carbide so tooling resharp becomes more relevant.
It's been my experience that for the most predictable outcome, just choose a carbide insert meant for hard turning. You'll change inserts more often, but its a small price to pay for the results.
Make sense?
