I had cut the slab into a 40"x40" piece for the coffee table top, and next needed to reduce it down from a 3" thickness to a 1.5" thickness. There were a few options as for how to do that slim-down, as noted in the previous post.
After much head scratching, I decided that the risk/reward for slicing a 3/8"~1/2" piece off of each face was not favorable, and decided that the safe course of action was to mill material off of each face in a series of rounds, letting the panel rest and move for a few days between rounds, was, regrettably, the best way to proceed. Yes, half the panel went up the dust collector, but this method gave the best chance of the desired outcome of a flat and stable tabletop.
I could have gone the route of many when faced with processing a slab of wood larger than their equipment (jointer and planer) can handle, namely fabricating a leveling and support system and some sort of giant router sled. I decided to go another route however, and took the slab to a CNC facility in upstate New York. I know that this would produce the flattest result, and I don't process large slabs too often so the fabrication of a large specialized jig, plus the rather boring nature of endless passes back and forth to mill the surfaces, led me to take a pass on that option. I also sent the CNC place a CAD drawing of the completed panel, as I wanted them to also use a ball mill to cut relief grooves on one side of the panel, in the hope that it would dampen down any tendency for the board to cup or curl with seasonal movement. I provided a detailed milling schedule as well, and discussed the matter at the company with the very person who would be doing the work. And that person would remain the same for the duration of the project. Just trying to forestall potential problems that can come up when sub-contracting a project phase.
The milling took place in three steps, which meant three separate set ups on the CNC router deck, which made the work a bit expensive, however what came out in the end was a dead flat board:
Click on the picture for a larger view. The 'working' surface of the slab, shown above, is the face which is closer to the pith of the tree. The wood is looking quite spectacular, like a 'topo map'. If I had wiped it with alcohol for photographic purposes the figure would be more apparent to see, but I left off doing that.
On the backside, on the bark-facing side of the slab, the relief kerfs were milled just as designed:
The middle kerf is shorter as there will be a central tenon at that location. Please note that while the board is at finish width, it remains an inch long on each end at this stage.
Another view of the grooves:
I've applied a coat of anchor seal wax to the board ends to dampen down any moisture exchange and will let the slab sit for a while -several weeks at least- and keep an eye on it to see what movement tendencies it may have. Fingers crossed of course! I'm sending happy thoughts towards the piece - stable...stable...stable....
I'm contemplating making a slight revision to the breadboard end design, and am waiting and watching the board first to see what it has to say.
Thanks for coming by the Carpentry Way. On to post 8.