Peter Follansbee and Mike Siemsen
have cleared up the mystery of the pinwheel-shaped wooden nails. The
pinwheel shape of the nails is caused by the shell or gimlet bit used to
make the hole. The long edges of the bit bite into the grain, tearing
it. When the peg is driven into the hole, it takes the shape of the
Siemsen demonstrated this process with a square peg. Follansbee (who took the photo above) uses more of an octagonal shape.
Shell bits are similar to spoon bits and aren’t used much anymore (you can read about them here on the Full Chisel
blog). I’ve used spoon bits in chairmaking and have noticed that they
do tend to tear at the end grain in a hole, but I’d never seen such
dramatic deformation in a peg. I use a lot of dry oak pegs when
drawboring and have noticed that in my work it’s the hole that tends to
deform instead of the peg. So I might start with a round hole that turns
into an octagon as the peg is driven in.
In any case, thanks to Peter and Mike for setting us all straight.
— Christopher Schwarz