On Tuesday, January 12, 2016 at 1:59:13 PM UTC-8, amdx wrote:
I have one of the Harbor Freight 7 x 10 lathes.
I have a bicycle seat post that I want to reduce the diameter by 0.025".
[but it's a 12" post}

One out-of-the-box suggestion: turn a tapered steel mandrel that
goes from x inch diameter to x - 0.027". Get a honkin' big hammer
and drive it down the seat tube. Use lubricant, and start at the
narrow end of the mandrel, of course.