Building a stack
Once the boards are ready to go the next step is to sort thru them and find nine that make a reasonable stack. The boards don’t have to be perfectly straight so long as they’re all not perfectly straight in pretty much the same way. It’s okay if the stack is a bit bowed end-to-end… we’ll correct that later. The most important part of selecting boards to form a stack is that they are as similar as possible, so the broad sides are as close to smooth as you can get them. We’ll need to make them perfectly smooth later, so the better you start off the less waste there will be later.
Once you have a set of boards ready to go, lay them out on a bench in the order and orientation that you’ll be needing them during glue up.
I use 8 pipe clamps, each with 12” wide 2” x 2” oak cauls on each side. I will alternate these on each side of the stack as I clamp it, so I start with half of the clamps on my workbench spaced to ensure that the other half wont overlap them much. I place butchers paper under the clamps to protect the workbench from the dripping glue later.
I use Polyurethane glue for my stacks because it has a reasonably long working time, and it will take about 15 min to actually get a single stack clamped up. I take the cap off the bottle and pour a bead of glue down the entire length of the first board, then spread it with a plastic spreader the same way I spread epoxy during layup. (I use old bits of base material as a spreader here.) It takes some practice to start to recognize how much glue to apply in a single pass. Start with too little and add more but don’t take too much time as there are seven more applications to make. Take the next board and lay it in place on top of the first one, then rinse and repeat. Once the final board is in place you’ll have a gooey stack ready to be clamped. Carefully push the stack over so it lays flat on the bottom set of clamps and adjust the board placement as necessary. Note that the ends of the stack don’t have to align perfectly! It’s common to have boards of slightly different lengths and that’s okay; we’ll trim it up later.
Once the boards are aligned, tighten the center clamp on the bottom, then add top clamps on either side and tighten them. Tighten two bottom clamps on either side of those, and so on until you reach the ends. Try to avoid getting any glue on the cauls so you don’t glue your clamps to the stack, or take precautions like tape on the cauls.
I usually let a stack dry for3-4 hours so I can make a few stacks per day.
The clamps: Pipe Clamps
The Woodworking Resources page has a number of articles on proper clamping. These are all worth a read and will help you understand how much pressure you should use in order to get a good glue up.
Preparing the stack for slicing
Once the stack is dry and out of the clamps it need to be prepared to be sliced. The wide sides of the stack will be uneven, since it’s almost impossible to find boards that are perfectly straight, and to align them perfectly for clamping. I first pick the side that looks the flattest and remove the excess glue with a scraper. Next, I run that side over a 8” jointer until it is flat. Once that face is flat, I turn the stack 90 degrees and flatten the bottom of the stack using the newly flat face against the fence of the jointer. Now we have one flat wide face, one flat adjacent base and those two surfaces are at 90 degrees to each other. Next, I flatten the other wide face by running the stack thru a planer with the jointed side down. This yields a stack which has two good sides, and one good base. Surfacing the fourth face is optional at this point and I usually skip it. I then take the stack over to my chop saw and trim the ragged ends square.
Finally, clearly mark the bottom of the slice with a few triangles along the length. This will help you identify the bottom of the slices later for book-matching.
The stack is now ready for slicing.
- Pictures, pictures, pictures! Each stage of glue up, and pics to make the final stack preparation clearer.