Resawing Lumber

The Snowflake, Bandsaw in Residence

A note came into the Studio mailbox asking this question:

“While resawing a flatsawn 3/4″ black walnut board, the board cupped. Then after letting the board acclimate for 30 days I hand planed the one face flat and then thru the bench top planer. The board cupped again by the next day, Is there a way to have the lumber come out flat and stay flat?”

There are too many variables in this question to give a simple answer. Was the wood dry or properly kiln dried? If not, then a moisture imbalance occurred when you resawed. Did you resaw right down the middle of the board? If so, then cupping towards the cut is very common on both boards. Wood here gets wetter on the outside than the inside that has been kiln dried. Sitting around the lumber yard or even in your shop, the wood will take on moisture on the outer faces and stay dry in the middle. Let it sit for a year and you may avoid these problems. Did you take more wood off one face than the other when planing it? This can expose a wetter surface to the air as well. Putting the board under the pressure of the feed rolls can also make some wood respond badly.

Finally did you pray to the gods for flat wood before embarking on this perilous journey? A proper sacrifice to the gods of flat lumber is advisable in most situations.

All these things can come into play when trying to resaw wood and keep it flat. I wish you luck.

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One Response to Resawing Lumber

  1. Jim Podesva says:

    What our friend means is that wood moves in response to moisture and air. There is really nothing you can do to eliminate it completely. You can minimize it, but never eliminate the phenomenon altogether. The rule of thumb is (1) start with a thicker board than what you need, and make sure you have at least 1/4 inch more than what you need (after you re-saw) on both halves, (2) when you re-saw, let the board sit for 24 or 48 hours on stickers that allow the air to circulate around the material to see how it will move, (3) after it sits, straighten and thickness your board by taking material more or less equally from both sides — and remember that one side of the board was the center of a larger piece of material up until 24 hours earlier; so you might need to take more material off the opposite side to reach equilibrium, and (4) after all that — pray to whatever god you favor that the board comes out and stays flat. In the end there are no guarantees.

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