i usually do it by hand. spit, then burnish, then dye, then gum trag, then burnish.
i just converted(kind of) this table top buffer from Harbor Freight.
left side is a cotton buffing wheel. right side is the same, but covered with denim. makes edges like this.
the line running down is my fault.
i'll probably stick to doing it by hand unless i can get this smoother.
but i've been doing leather work for 2 months, so i'm sure i'll get better.