Wood selection, drying, and prep
You can make a core blank out of pretty much any type of wood. The only wood I use in my blanks is poplar; I add a bit of ash along the edge of the core later when adding sidewalls. Many people use combinations of various types of wood throughout the core, in different patterns. Almost anything will work, so be creative.
No matter which type of wood you use, selecting quality boards is critical. You want clear boards with even grain, no knots, and preferably as straight as possible. Ideally all of the boards should be a bit longer than the final core blank length.
The best place to source your core wood is a dedicated lumber yard that sells rough cut wood. It is rarely cost-effective to get your wood at a big-box store like Home Depot or Lowes, even if they have the wood you want. In the Seattle area there are many excellent options. I always get my core wood from Compton Lumber. They have an excellent selection of rough poplar as well as poplar already machined to the size I need. I also get my ash from them, always rough cut. You can spend the time at a place like Compton to pick through their stacks of wood and find just the boards you’re looking for.
Purchasing wood from a real hardwood supplier is often confusing. There are a lot of odd terms that you may not initially be familiar with. The Language of the Lumberyard at Fine Woodworking is a good introduction to the topic, as is the video blog entry A Lumbering Feeling from The Wood Whisperer.
You want FAS (firsts and seconds), as clear as possible, and straight with minimal twisting or bowing. If you want it already prepared so you don’t need to do much work to the wood get S4S (surfaced on four sides). Note that if a board has a knot or other blemish near the end it may be alright. Often blanks come out much longer than they need to be and a knot near the end would not be included in the final core when cut.
Preparing the boards
We need poplar boards which are at least 7’ long, 2.5” wide, and about 0.75” thick, and we’ll need nine per stack. Happily, Compton Lumber sells poplar already machined perfectly to 2.5” wide and 0.75” thick in lengths ranging from 6’-8’. If I find a bunch of 6’ board I’ll tend to make some blanks for shorter boards… these blanks will tend to end up about 175-180cm long, which can yield cores of 173-178cm.
If you can’t find your wood already cut as you need then you can start from rough stock. This is the way I used to start before I got lucky with Compton. There is an excellent article from Fine Woodworking on turning rough cut lumber into useful boards here: @TODO. Following this process requires a table saw, a jointer, and a planer, all of which you need anyway for steps later in the process. It takes some extra time to do this, in particular some extra acclimation time for the wood (see below), but it’s a bit cheaper to start with rough wood that it is to buy it pre-machined, and you can customize the thickness of the strips in your core.
Acclimating the wood to your shop
No matter how you get your boards you need to first let them adjust to the climate in your shop. Wood moves with moisture changes, and the moisture content of your shop if often quite different than the place you bought it from. Stack the wood on a flat bench with “stickers” in between; small pieces of wood used to separate the boards and let air flow around them. Place some heavier boards on the top of the stack to help ensure that the wood remains as flat as possible, and make sure that the stickers line up one on top of the other. Let the wood rest in your shop for at least a few days if you have narrow boards, and longer for thicker/wider boards. The wood will change shape slightly then stabilize. It’s better for it to change shape before you try to build something with it than during or afterwards.
- Article link on taking wood from rough to S4S.