How to draw celtic knotwork from "Celtic Knotwork", by Iain Bain, Constable London, ISBN 0 09 469810 4
1)
Draw the grid. u is the unit of measurment.
2)
Mark off a margin, width n (1/2u) all around the pattern.
3)
Spot the quarter-points, (1/2n or 1/4u) all around the pattern.
4) Draw
in the diagonals.
5) Extend
the diagonals that intersect the grid lines.
6) Draw
the outter curves of the cords. Merge those at the ends into the boarder.
Avoid kinks and reverse curves.
7) Draw
the inner curves maintaining the cord thickness. Complete the corners with
short straight lines.
8) Erase
the lines to form a braid.