Hey Assaf, congrats on embarking on your bench build! Here are a few lessons I've learned from building pieces that are based on large face laminations. Take them for what they're worth, and there are lots of good tips already in this thread as well. And, if you haven't yet, you may check out The Anarchist's Workbench from Lost Art Press. The pdf of the book is free, and even though your design isn't the same it has a lot info that applies to designs that use face laminations.
It's hard to say how much yield you can get from your lumber without seeing it. However, with face laminations remember that the faces can have defects (within reason) because the faces will be glued together, which will stabilize and hide the defects. So as long as the defects don't extend to the edges, you're good. For the bench top, I honestly just look for one clean edge; you put the other edge with defects on the bottom. Considering this, I bet you can get pretty long boards out of your rough stock. You really only need two boards with a clean face for the outsides of each lamination.
Getting bow and twist completely out of the length of long boards can be somewhat challenging. If you can get them "pretty good" (but not necessarily perfect), your clamps will pull them straight during the glue up. Same goes for if they move after planing. If it's just a little, don't worry about it and strong-arm them with the clamps. Doing a dry run with the clamps to see if they can pull the gaps closed will show you if you need to do more work or not.
Orienting the boards with matching grain direction if possible is a good suggestion as it'll make flattening the top easier. If it's not possible and/or the top is giving you fits with hand planes, you could rig up flattening jig for your router as was recommended previously.
I wouldn't worry too much about getting the edges aligned perfectly with cauls. If you've got everything reasonably straight with your No. 7 and your clamps are sitting in the same plane, putting the jointed edges facing down on the clamps should make that side come out reasonably flat without cauls. It'll probably be easier to flatten any slight misalignments afterwards than potentially chasing your tail during the glue-up with a caul system. Hard to say for sure though without seeing the prepped lumber and your clamp set up.
As for the number of clamps, as many as you can get your hands on of course
. I find with thick laminations it helps to have clamps along the top and bottom (as opposed to just a single row of parallel clamps). 3/4" pipe clamps would work well, maybe 6-8 on each side? You might start with four or five on each side, then add additional clamps where there are gaps.
Hope that helps, and good luck!
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Originally Posted by Jim Matthews
