If the dimensions are not too critical, I reckon it could be done with an electric drill (corded or cordless, but with variable speed so you can run it slowly), a file and some way of supporting the rod.
For the supports, make up a baseplate with two uprights, about 2.25" apart, each with a 3/8" hole in it. Start with just over 33" of rod, and pass it through the holes so it will rotate. Power the rod's outer end with the drill, and use a file followed by emery paper (and then metal polish if you need a smooth surface) to reduce its diameter between the uprights. Once you have got it down to your "0.345" or so", cut the unwanted bit off the end so you are left with 2" of the reduced diameter.
Some lube in the crude 3/8" bearings would help, and might stop them marking the plastic too much. But oil or grease sometimes makes wood swell sightly, which might cause binding, so if you use wooden uprights, a wax-based furniture polish might be a better choice. If you can find some aluminium say 1/2" thick, that would be a better option for the uprights, though it might involve you in unwanted metalwork in fastening the uprights to the base.
Andy
