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Chris, it sounds to me like your lathe headstock may be angled just a bit. If that is the case then even taking multiple passes at the same setting can still result in a taper. Not sure how long your cylinder is but it wouldn't take much to misalignment to give you a tapered bore though .010" sounds like a lot if the cylinder is pretty short.Put a good piece of truly round stock in the lathe and use a dial test indicator. As you move along the round bar, check to see if you are getting any indicator movement. My suspicion is that you will get some, meaning the headstock is out of alignment even if by only a fraction of a degree.Bill
I mounted a Dial indicator perpendicular to the chuck. Spinned the chuck around and saw that it varies from 0 to 3 thou. I moved the saddle to about how much my work piece was and noted that it varied about 1.5 thou.