Cupped Wooden Slabs, How to Flatten and Join

How did you store them after you bought them?
They should have been stickered so that air could circulate all around them.

What you propose is really the only option. But if they aren’t completely dry, they may warp again after you flatten them.

-- Gerry, http://www.thecncwoodworker.com/index.html http://www.jointcam.com

If you flip the slabs will they flatten out a bit? Probably only helpful if they weren’t stickered while acclimating initially

One other quick option if u haven’t already built the router sled – you could build a jointing sled for the planet (assuming your planet can accommodate the 18” per your plan).

First, get a moisture meter to make sure these slabs are at ideal workable dryness. I’d use a handplane to knockdown and flatten the concave sides… find a shop with a timesaver and call it done…

When I initially stored them I laid them on their sides (lengthwise against the wall) with spacers in between. The I noticed the cupping issue so I tried laying them down such that the legs of the rainbow were facing up. Then I used a wet sponge for a few days to try and expand the fibers on the drier side. I did that for about three days but it doesn’t seem to have done much. I am now storing them upright but they each have their own spot on the wall.

I was told they were kiln dried so I assumed they were dried properly, but I do think it would be a good idea to get a moisture meter to see the difference between both sides. Any recommendations for good ones on the market?

First, get a moisture meter to make sure these slabs are at ideal workable dryness. I d use a handplane to knockdown and flatten the concave sides… find a shop with a timesaver and call it done…

- Logan Windram

How would I go about doing this hand planing operation precisely if I do?

Natzem,

The router sled idea could achieve the flat slabs you are after; as could other methods. However, a great deal of thickness could be lost leaving slabs a little too thin.

Another option, after the slabs have fully acclimated, would be to rip the 18”wide right slab to narrower widths and flatten and then plane the ripped slabs. Narrower the ripped pieces would result in less material removal for flattening. After jointing the ripped edges, the slabs could be glued back to re-form wide slabs, although a bit narrower than the originals. Unfortunately if internal stresses exist in the ripped slab, a fair amount of material would have to be removed from the edges to produce straight glue lines. I know of no way to determine whether any internal stresses are present in the right slab.

The left slab does not look too bad from the photo.

I can offer no advice on moisture meters and since I am not proficient with hand planes, I will remain silent on hand planning techniques.