Hi. I make a bunch of various sized gear blanks on a CNC lathe from either 9310 or 4140. Average bore size is about .188, and I need to hold .0005" tolerance on that bore. I've been making the parts using solid carbide boring bars. When I make a job out of 4140, I can usually make about 2000 parts without having a single part undersize on the bore. With 9310, it's a different story. I'm always struggling to keep the bore size off the bottom. My best results so far are with a brand new TiN coated tool, but once that tool starts to get just a little dull, the bore size starts closing up on me. I originally tried reaming with a HSS tool, but that was awful. The material just welded to the tool and cut oversize or tapered right away. I was using oil, by the way. Anyway, I'm wondering what you would do? I'm fine making the 4140 parts, but with the 9310 should I stick with the boring bar and just keep sharpening / changing bars frequently, or should I go back to reaming? Maybe trying a coated and/ or carbide reamer? Thoughts?