PM-1640TL problems getting reasonable surface finish

1045,1144sp ,303 stainless, 416 stainless all seem to machine well, even on smaller machines with HSS
 
Are you using the inserts that came with the Accusize tool set? If so I suggest getting some quality, name brand inserts, Korloy, Iscar, Kennametal, Tungaloy. @davidpbest on this site has written a book on lathe insert tooling, well worth the cost of the book. While mild steel doesn't turn the best, you should be able to get better results.
 
Also, carbide likes at least 200 SFM at a minimum, so ( 200 sfm x 12 in/ft) / (pi x diameter in inches). For 1/2inch stock, that comes out to roughly 1600 rpm. 400 SFM isn’t unreasonable although your lathe probably won’t spin at 3200 rpm.
 
There's a reason they make special files just for lathes. We do what it takes to get the finish we want, it's not cheating to sneak up on the dimension you're shooting for with emery paper.

John
 
That is a mighty small diameter you are cutting. You will have more control over chip production with a hand-ground braised carbide tool. The tool pressure which most carbide inserts need to cut (due to their edge geometry), can encourage more of a smearing (versus cutting) action on small diameters. Tools for cutting small diameters gain a benefit from a smaller radius Chip Breaker groove cut into them. A stone honed edge helps as well. They guys who work with "mini-lathes" are constantly dealing with small diameter parts. It may be counter intuitive, but read some of the tool-grinding postings by the folks who have the 7 X 12/14/16 and Sherline lathes. They swim in these waters daily. They get great finishes, even with less horsepower and rigidity.
 
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