Treenails, or "trunnals" are made in the following fashion around here
(includes Dutch and English history):
  Start with a dry section of a hardwood tree the length of the nail that
you want (if you are using 10 inch timbers the total length will be 10
inches. It is not necessary for either end to be protruding (you of course
may like that look but the ends of the pegs can in fact interfere with the
finishing of the work).
  I use a froe to split the log into 1 inch slabs. I then split the one inch
slabs into 1 inch square pegs. Normally at this point I go to the shaving
horse and take a small bit off each square edge. The pegs are more square
than octagon - you have heard of a square peg in a round hole - well that is
exactly what you want. One end of the peg is sharpened, starting only about
an inch back from the end giving a rather short point.
  When you have bored the one inch hole through the mortise you insert the
tennon and mark the spot in the tennon where the hole would like up. Take
the tennon out and move about 1/16 of an inch in the tennon toward the cheek
and there drill the one inch hole. This will cause the joint to tighten up
when the peg is hammered through the assembly.
  It really is best to use green wood for the frame and dry wood for the
pegs as they will tighten up greatly as it all dries out. By green wood I do
not necessarily mean just fallen timbers, it is normal to fell the trees in
the winter and then build the structure the following spring and summer.
This is so that the majority of the sap is down in the roots and not in the
tree itself.

> -----Original Message-----
> Off-hand I'd say I'll be needing at least a couple hundred
> treenails.  Is there some trick to producing these in a timely
> fashion, or does one have to hack them out one at a time using
> a hatchet ?  Hewing each one by hand could easily amount to
> the most time-consuming operation of the whole construction.