Why do I get a taper when turning?

[Robin Hewitt]

Face the end, that will tell you if you have the tool height spot on.

Only possible culprit I can add to the above is angle the tool edge 5 past 12 on the clock. That way it pushes against the work rather than pulling on it. If it shies away from the tool you can fetch it square on the next pass. If angled 5 to 12 you expect a crummy finish and awkward taper.