Chucked a 1" X 2 1/2" steel round bar in the 3-jaw chuck. Took small outside cuts to clean and ensure concentricity. Faced the end and relieved all but 0.150" around the rim. Swapped ends in the 3-jaw, faced, center drilled and slightly trimmed the diameter of a 1/2" or so to show the other end is the "square". Drilled through with a #36 drill bit in increments of 0.075" to remove chips. Expanded the hole with a #22 drill bit followed by a #6 drill bit. Repeated to deliver two very accurate cylindrical squares.
Use of the four jaw chuck may have been a better choice.