Ken is spot on with his observation regarding the names given to carbide turning tools.
The square, Rougher, cutter actually finishes better on a pen blank. It acts kind of like a tiny hand plane when moving across a straight spindle, the straight edge shears wood fibers evenly at a uniform depth leaving a flat more glass-like finish that usually permits sanding to start with a much higher grit. They were called roughers by industry because their initial intent anyway was to knock down the corners and irregular areas of a blank. They are much more stable than round cutters to do this job because they resist twisting or catching when hitting uneven edges, so the idea was that they would be used for the roughing phase of turning.
The round, Finisher, cutter actuality roughs in blanks better because round cutters concentrate all of the cutting pressure onto one small, focused area. This lets it dive deeply through wood fibers with less effort making it efficient at hogging out material, i.e. roughing. However, because the cutter is round, every pass essentially cuts a "U-shaped" groove which in actuality makes the surface rougher than a square flat tool. They got the Finisher name because the round cutter can create a more fluid geometry, seamlessly transitioning through curves and coves without sharp corners that would dig into the wood. Since it is better at defining a fluid curved shape manufacturers dubbed it as a Finisher.
Their names certainly are counterintuitive with how many pen turners (such as myself) use them.
For square cutters anyway, industry did try to bridge the gap by making square cutters with radiused corners. This was their attempt to provide the flat, plaining benefit of the square cutter but with the the rounded corners to help eliminate the risk of gouges/catches from their sharp edges. These work very good for making smooth finishing passes to pen blanks (except where there are tight curves or coves of course).
Dave
