aah... purpleheart.... beautiful..... and burns if I look at it sideways.... and the burn marks are terribly stubborn to remove
I always have the same problem with purpleheart unless I use VERY light passes with the router or sander... finer grits of sandpaper seem to burn things so fast that I can't react in time (just ask my drum sander.... I've lost a sanding belt to purpleheart burning... it couldn't be salvaged even with little green)
I wish you luck and double berts suggestion that you sand end grain farther to seal it and create even grain soak, but purpleheart (and bloodwood for that matter) really require extra effort to minimize burning. You may want to try sanding minimally with rough grain and then sealing the end grain with shellac and then sanding by hand... this worked for a stopper I made
Lawrence