After another week with the planer, here are a few more observations. Even though the cutting depth is only 1/16th of an inch, that’s a fair amount of soap for the size bars I make. My Plan B is to plan for planing! I have also discovered that planing is not a good way to “square up” a soap bar. The planer is well designed to cut a uniform slice of soap from whatever edge is being planed. If the sides weren’t square to begin with, they’re not going to be square after planing.
Although there’s more waste, and the planer can’t compensate for my bad slab cutting skills, planing and beveling definitely produce prettier soap.