reaming vs. boring steel alloy

[wmpy]

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?

[mc_n_g]

What state is the 9310 in? Is it getting hardened after your operations?
Are you running the reamer at least 1/2 the speed of a HSS drillbit? The only other thing I can think of is you should only be cutting about 0.010" to 0.025" with the reamer (meaning the hole should be undersize by 0.010" to 0.025" before reaming).

[wmpy]

The 9310 is annealed, and yes, it gets hardened after my operations. I don't remember exactly, but I believe I was leaving about .010" for reaming and running it about 40 sfm.

[christinandavid]

Have you had any success reaming any type of material on said machine?

DP

[wmpy]

Actually, no, I don't think I have ever reamed on this machine. I much prefer to bore when I can. If you're thinking that the machine might be out of alignment... it's a gang-tool lathe, so I aligned the holder with an indicator to be in line with the spindle. I tried holding the reamer rigidly and also in a floating holder. No luck.

[dertsap]

Originally Posted by wmpy ? Maybe trying a coated and/ or carbide reamer? Thoughts?

best bet would most likely be a solid carbide reamer that is dialed in dead nuts

[wmpy]

I think I'll try that. Do you recommend a floating holder? or holding rigidly?

[dertsap]

rigid and dialed in dead nuts

[mc_n_g]

I think your reaming speed is at the low end of recommended drilling SFM. I think you are reaming too fast for HSS is low carbon. I would say 10-15 SFM for the HSS reamer rather than 40 SFM in that material. You might be smoking the reamer and forcing the galling.