Bubinga slab top

[Chris Hall]

I've been watching the bubinga slab top in my shop for the past two weeks. It's an expensive chunk of wood and comes from a grade and size of slab which likely will never be seen again, so I am on pins and needles. I have done all i could think of to make it possible to use a thick flat-sawn slab and not have problems with movement. It's a challenging problem.

My solution has been to mill the 3" thick lab down over a two week period in increments, letting the board sit and move between steps. Then I figured that if a series of relief grooves were cut on the bark side of the slab would effectively neutralize the ability of the slab to move.

But you know, these are ideas and theories and solid wood cannot be predicted entirely. That's why I like solid wood - never boring!

The board, when i picked it up from the company that machined it down to 1.5" thick, was very slightly cupped towards the bark side. A 0.5mm gap -1/32" could be seen in the middle of the board with a straightedge laid across. That was how the board had moved in the 4 or 5 days since the final milling step.

I brought the board to my shop and set it up on an old table saw that is stored a few feet from my space. I left it alone for a couple of days and reinspected. Now it had bowed the opposite direction, towards the pith side, by about 1/16". I was a bit concerned, wondering where things were heading. I obtained a slab of metal weighing close to 100lbs and parked it on the middle of the board to force it back down, and added several clamps across the width.

I checked the next day and saw that it was now sagged in the opposite direction by nearly 1/16", so i removed the weight and left the clamps on. I also raised it onto 3" sticks so there was better air circulation.

Now a couple of weeks on, I have concluded that the relief grooves have worked as I had planned. While the board can still move up and down with humidity gain/loss, it is clear to me that the resilience of the board is much lower - it is very easy to push it back into a flat position. I am quite optimistic that the frame of the table will be more than enough to keep the table slab flat over time.

The relief grooves, therefore, have me grooving in relief!

Should be starting in on cutting the legs and apron parts tomorrow.

[Yxoc]

Congratulations Chris!

I really admire your work. You take great risks, putting your reputation and client's money on the line to create things that most people don't understand let alone produce. In this case with a piece of wood that is literally a jewel due to its rarity and cost. Your technical understanding of the medium has paid big dividends here.
Can't wait to see how the rest of the build progresses.
Regards

Derek

[John Whitley]

Glad to hear the bubinga top is working out. I've been following that project with some interest. Not sure I'll ever work with wood of that scale or that rarity, but it's incredibly valuable to get a view into the strategies you've been contemplating for handling this material.

[Chris Hall]

I guess I hope to show with this project is that a slab with a significant band of flatsawn wood can be used in a way which controls movement and yet allows for it. So many assume that schmeer is the only way to achieve the visual of a continuous wide surface with stability.

The safe alternative would have been to do a frame and panel top with dovetailed battens underneath - a very traditional and sound form of construction. With frame and panel tops though, you need those expansion gaps, which, on a tabletop, are places for crud to accumulate. It remains one of the back up plans though.

I am very fortunate as well to have a client who is willing to both take the financial plunge of buying this large slab of wood and who allows me a lot of freedom on the creative side. It's a rare combination, in my experience at least.

I appreciate the kind words.