I often approximate roundovers by taking several passes over the edges
at different angles with a small palm plane until the edge feels round.
When just a few edges need doing, this is much more convenient than
setting up a router. But I was starting to wonder how many passes
at what angles would be ideal.
I started playing around with the concept. Just sketching it by
hand, I concluded four or five initial passes at 45 degrees would be best,
but then I drew it up in CAD. It turns out, five
strokes at 45 degrees, followed by one stroke each at 22.5 degrees from either
side will approximate a circular roundover almost perfectly, with the radius
12 times the shaving thickness.
If I want the edge to feel really smooth, I'll go over it briefly with some
coarse sandpaper. At left, cutting through the middle of the piece I was
demonstrating with above, followed by sanding, and you
can see the edge really is a roundover.
I also use a small palm plane if I just want a chamfer.
Of course, there are dedicated chamfer and roundover planes to do this sort
of thing, but in my view, these don't work as well as just a palm plane. The problem
with chamfer and roundover planes is that there is nothing to prevent the plane
from cutting full depth on one pass. That's usually too much, and it makes
a mess of the wood. So my preference is to just take many passes with a small plane.