Although you don't need to know exactly how to mill a log into usable lumber, it certainly will help you choose you lumber wisely.

The process of taking a whole log and sawing it into usable lumber is quite simple. After a tree is fell it must be cut or bucked into usable lengths depending on the capacity of the mill. Usually 8 - 12 feet is a standard length of log. The log is put onto the mill and boards are cut.

There are a couple of ways of milling lumber: plains sawn vs. quarter sawn

There are some variations in the way lumber is milled. The first and most common method is plain sawn. This is how most commercial lumber is milled. Boards are milled from the log until about 1/3 of the diameter has been sawn. The log is then turned 90 degrees and the process is repeated.

This method yields boards with and arched pattern on the face of the board, and the end grain of each board will show a series of concentric arches. Boards milled from the outer edge of the log will be more stable then those closer to the middle.

Another method to mill a log is to quarter saw it. This method yields high quality boards that are more stable and less likely to expand then plain sawn lumber is.

With quarter sawn lumber a log is first milled in half and then into quarters. The quartered logs are sawn into boards. Since the grain on quarter sawn lumber runs vertical through the lumber it is less likely to cup or bow then lumber using the plain sawn method. This makes it ideal for large glue-ups like table tops or shelves. Quarter sawn lumber takes more effort to mill and there is more waste, this result in higher cost.

Drying lumber

Once a log has been milled into lumber it is stacked with a spacer strip between each layer. This promotes air movement which helps the lumber dry (season). In most cases this is all that is needed to be done for the lumber to dry. In an ideal situation you could leave a stack of freshly milled lumber in a covered structure with open sides for 4 - 6 weeks (during the summer). The air movement will be enough to dry the lumber to about 15% moisture content. In the long term a piece of wood will find a balance with the natural relative humidity.

Alternatively when you want to have production milling a kiln will be used to speed up the drying process. A kiln will simply bake the moisture out of the lumber. After the lumber has reached its desired moisture content (6% - 8%). It can be stacked and covered and left outdoors for the short term but for long term storage, lumber should be stacked indoors.

It is important that lumber remains in neat stacks that have wood strips dividing each row of lumber. This will ensure that the lumber remains straight. If the humidity where the lumber is being stored is too high it will need to be reduced. Obviously if your lumber is stacked outdoors you will need to move it inside but if your wood is indoors a de-humidifier will be needed to reduce and maintain a lower humidity level.

I believe it is important to know the basics of how lumber gets to the lumber yard. This allows you to make wise choices about which stock to choose and when a lessor grade of material will be sufficient.