Flattening Really Wide Boards

Years ago I came to possess a really large walnut log and had it sawn to my specifications on a band mill. I then air dried it and have stowed most of it ever since. Many of the plain-sliced slabs yielded widths of between 20″ and 33″. Yes, I consider myself a lucky man.

I’ve used a few of the wide slabs over the years for special projects, mostly tabletops and doors where the beautifully colored walnut displays all its glory. And no, I don’t rip the boards into narrow pieces and glue them back. I just use these wide pieces as they are.

But wide stock like this can be problematic when it comes to flattening it. Jointers don’t have the capacity and sending it through a planer, even if you had one that big, would not remove twist or cupping. Flattening could be done with handplanes, but I don’t have the requisite planes and blades; besides, it’s not my style of working.

So over the years I’ve tackled the problem by doing some work with one handplane then switching to an 18″ “C-arm” drum sander. First, I make sure that the board I’ve selected is reasonably flat to begin with. Most of my stock is, because I stickered it carefully while drying it. And this log, and maybe walnut in general, didn’t have a lot of stress in it.

I put the board on my bench and assess how much twist may be in it by looking at the corners. Are any off the table and by how much? Next I use a straightedge the check across the width for high/low spots. There usually are some near a knot or at the edges of the new wood growth.

When I’ve made these determinations, I use my handplane to knock down the high spots and the corners that show the twist. By flipping the board to the side I’ve planed, I can reference the side to my flat benchtop. This work may take 15 minutes at most.

Next I go to the drum sander with an #80-grit belt installed. The thing about these relatively small drum sanders is the infeed and outfeed rollers that hold the work down don’t really exert much pressure like a planer does, and therefore they don’t force the stock flat to the table. The other thing is, I’ve found these sanders will consistently sand widths wider than their 18″ capacity with differences edge to edge of only a few thousandths. All you do is turn the board and send through the portion that didn’t pass under the sanding drum on the first pass.

Because only light passes are possible on these machines, they will first sand high spots on the board. And because the side that will be reasonably flat from the handplaning is always down, you just keep sanding the one side until it is uniformly sanded. Then you turn the board over and follow the same procedure on the opposing face. Depending on the board, the whole process may require 30 passes or more in all. Then, when both faces are cleaned up, I switch to a #120-grit belt for a couple passes to get rid of the coarse sanding scratches.

I won’t claim the process leaves this wide stock dead flat. But given it’s width, and given that it’s often being used for a top of some sort, any minor twisting can be pulled out when fastening it to it’s base. Using the sander this way has been effective for me. My only complaint is it can be a bit boring.

– Steve Shanesy