I use a Harbor Freight saw now. Had to buy the carbide discs separately. The metal blade it comes with is too coarse, IMO.
Before that I used a hack saw. First put a layer of masking tape around the shaft where you're going to cut. Then lay the shaft alongside a (1x4) board using the squared end of board as a guide to get a straight cut. Saw gently. Remove the tape and use a sanding block to true up the edge, again using the end of the board as a guide. Slightly champfer the outside edge with sandpaper. QED.