Many people ask why its so hard to find very thick wood such as 3 or 4 inch thick. When kiln drying, every time the thickness is doubled, the defect rate, or the number or things that happen to the wood to make it undesirable, squares. In addition, the amount of time it takes to dry the wood also doubles. So 2 inch thick wood will have 4 times the drying defects, and 3 inch wood will have 9 times the drying defects. There is a tool to produce the thicker wood, it is called a vacuum kiln, and they start at about $100,000, a little out of reach for us. It is possible to air dry thick stock, but it also takes a very long time, the last load I did took 18 months.
I have been asked several times about lumber grading in the past few years. The best and easiest way to understand that process is found on Robert Milton's web site. I have copied and pasted that below. Now just remember this is not log grading, but lumber grading. There is a big difference between them. Hope this helps those that are wanting to increase their education on this subject.
FAS or "Clear, Select" FAS or "Clear, Select" grade, which derives from an original grade "First And Seconds", will provide the user with long, clear cuttings - best suited for high quality furniture, interior joinery and solid wood mouldings. Minimum board size is 6" and wider and 8' and longer. The FAS grade includes a range of boards that yield from 83% clear-wood cuttings over the entire surface of the board. Number 1 Common (No. 1C) or "Cabinet Grade" The Number 1 Common grade is often referred to as the Cabinet grade in the USA because of its adaptability to the standard sizes of kitchen cabinet doors used throughout the United States. Number 1 Common is widely used in the manufacture of furniture parts as well for this same reason. The Number 1 Common grades includes boards that are a minimum of 3" wide and 4' long and will yield clear face cuttings from 66 2⁄3% (8⁄12ths) up to, but not including, the minimum requirement for FAS (83 1⁄3%). Number 2A Common (No. 2AC) or "Rustic" The Number 2A Common grade is often referred to as the Economy grade because of its price and suitability for a wide range of furniture parts. It is also the grade of choice for the US hardwood flooring industry. The Number 2A Common grade includes boards that are a minimum of 3" wide and 4' long that yield from 50% (6⁄12ths) up to, but not including, the minimum requirement for Number 1 Common (66 2⁄3%).
Post written by Robert Milton: https://www.hobbyhardwoodalabama.com