Flatten both sides of slab?

[Chris Groer]

I’m building a pool table that will have a live edge apron, about 8 inches wide and close to full 8/4 thickness. I’ve flattened the outward facing side of each piece and have jointed a flat edge opposite the live edge 90 degrees to the flat face. I started to get the planer ready to flatten the non outward facing faces but then it occurred to me that maybe there is no need since these faces will never be visible and I’m using T Nuts for the joinery. Is there any reason I need to flatten that other side? If it matters this is birch from a tree I cut down last year and had the 8/4 slabs all kiln dried. Thanks for any ideas

[mike stenson]

If it's flat enough for the joinery, it's flat enough. I don't even bother to do anything other than the minimal dimensioning needed on non-show sides anymore. Pretty much the same as pre-industrialized work.

[Dave Sabo]

I would.

There’s a school of thought that you need to surface both sides equally (or at least close) in order to keep it from warping in the future.

Same with sanding and finish.

[Randy Heinemann]

Whether to flatten in the "inside" would depend on how flat the boards are to start with. There is a lot of variation in how slabs are sold. Personally I'd plane the backside if you have outward facing side already flat. It might not need to be perfectly flat, but I wouldn't want to use a piece that isn't at least very close to being flat. Howeve, I'm kind of a perfectionist.

[Jim Becker]

Personally, I'd flatten the back/underside as it's a lot easier to work with material that's all the same thickness and it's also a positive thing for consistent wood movement over time. There's no need to get crazy and make it look as "perfect" as the money-side, but doing the deed is important. Dave also brings up an important point. In general it's a best practice to mill off the same amount from both sides of the material to reduce the risk for uneven movement caused by moisture content imbalance.