Most of the advice here is fine, but I would take exception to a couple of observations. A 20"dia. tree is more than adequate to generate any number of stock blanks. while it is true that a "boxed heart" will ultimately use up 4 to 6 inches of heartwood ( typically mills will use 4x6 for good quality logs, sometimes even less to maximize yield. This boxed heart ordinarily ends up as pallet wood or ties. boxing the heart is intended to contain the trees pith, which will indeed split and spoil any flitch that contains pith. However, if the log is flat-sawn (plain-sawn) through and through (called "in the boule", which is the way a great deal of European timber has traditionally been sawn -- and dried) you will end up with 20" "flitches", the centers of which will assuredly split or check. When the preliminary drying period has elapsed -- which will vary from locale to locale depending on relative humidity, wind conditions,etc., but will never get lower than the outdoor humidity and will need additional drying down in an indoor environment if you live in the northeast to achieve the 6 to 8 % moisture content required for stabilization. If you attempt to dry wood too rapidly, there will be significant degrade -- warp, checks, twist,etc. This is one reason why stock blanks take a long while to air dry safely -- and why, along with other reasons, that air dried stock blanks are generally considered superior to kiln dried blanks. It is a relatively simple matter to cut out both the pith and other defects from 20" flitches (slabs if you will) by laying out your stock blank dimensions in chalk and rough sawing with band saw, saber saw or other. The finest figure will be found, as others have stated, near the base of the tree and where the tree divides (crotch figure) and this figure will vary according to how the log was oriented when sawn through and through. You may achieve crotch feather or swirling configuration, all of it beautiful. The log may also be sawn conventionally by ripping bark and sapwood from each side and turning the log repeatedly to present the best face for a following plank ; again, the sawyer can still achieve 14, 16, 18" planks by sawing from two opposite sides until the pith will interfere. The remaining lumber sawn from the last two sides will give only 4 - 6" boards or planks.
