In the upper part of this shot, you can see a goodish surface, but notice the lines running the length of the work. They're very faint and can't be felt by hand, but they are there. I think that they're the marks of tool vibration caused by the chain drive. The Logan shaper is driven by a chain running on two sprockets. When sprockets wear, they tend to develop a bit of a hook in each tooth. The hooks grab the chain a little bit, possibly causing these small ridges in the surface.

I may replace the chain, but that's risky. A chain and a sprocket tend to wear together. If the wear is severe enough, a new chain will run worse than the old. It will have short links, while the teeth will want slightly longer (worn) links.

In any case, a final cut of about .001" seems to get rid of the ridge pattern, leaving a better finish. You can see that near the bottom of the photo, below the line of dust shaved from the iron by the cutter.