The final phase of creating a core blank is joining a pair of book-matched slices from a Slicing a stack to form a blank that is approximately 14” wide. (Of course, if you’re building skis then you don’t need to do this step, as one slice is plenty wide enough for a single ski!) The blank will be as long as the stack, which will at a minimum accommodate a board 180cm long. I create a small set of blanks each season that will yield a board up to 200cm long, but those are less frequently used. The thickness of the blank is determined by the thickness of the slices, with a goal of at least 0.400” thick to allow for the extra passes thru the planer required as a final core is formed.
The slices are joined with a little polyurethane glue along the center, and clamped with six or seven “4-way” clamps. These hold the slices perfectly aligned top-to-bottom while providing excellent pressure between the slices. You may notice some spacers in the pictures between the core and the clamps. These are to make up for the fact that most core blanks are thinner than the clamps are designed to accommodate. It’s a problem easily solved with a few strips of 1/4" hardboard waxed or taped a bit to prevent the glue from sticking.
I find that sometimes the edges of the slices aren’t perfectly straight because, after all, it’s difficult to get the top and bottom of such a heavy, long stack perfectly flat. I usually solve this by clamping my slices together and running the edges to be joined across the joiner in a few light passes. You could also rip them straight with a tablesaw and a jig.
When the blank comes out of the clamps it has a nice bead of dried glue along both sides, and some smear from the clamps. This is simply scraped off with a hand-scraper. The foamed poly glue isn’t very strong and comes off easily, leaving a core blank that is ready to finally become a core.