Reply by JBrow

  • Advertise with us

Posted on Question about warped slab. PLEASE HELP

View JBrow's profile


1368 posts in 1891 days

#1 posted 12-11-2016 03:51 AM


I suppose the question as to whether a top ½” out of flat is good enough to pass on to a client goes to whether this would be acceptable to the client and perhaps more importantly, to whether it meets your personal standards. But since you are asking whether a ¼” out of flat on two corners is good enough and your other comments, I suspect this slab does not meet your standards.

My guess is that at some point the slab was flat as advertised. But since then it has been improperly stored so that air could not circulate freely around the entire slab. I doubt that any effort to mechanically force the slab to flat will work. It is my belief that the forces in the wood are too great to be overcome mechanically. If the slab has been properly stored since arriving in your shop and remains warped, I can think of three ways to bring the slab back to flat.

The first is a lot of planing and sanding, which would reduce the thickness of the slab by ½”. This would be a lot of time and effort with pretty much guarantee unacceptable results; a flat but thinner slab.

The second option is canadianchips’ kerf method. While deep enough kerfs would allow the slab to flatten out with mechanical fasteners or mortises and glue, saw kerf cuts visible on the ends could be unacceptable. If the kerf cuts are made with a core box router bit, the kerfs would look nicer on the ends. The photos are of outdoor tables where I added core box bit kerf cuts 1/3 of the thickness of the top deep on the lower side of the tops. These were added to keep the originally flat tops flat; not make warped tops flat. In your case the depth of the kerfs may need to be a little deeper. Hopefully there is enough detail visible to show how this style of kerf cut look.

End table,up side down…

Coffee table with core box kerfs showing on the end…

The third method is to rip the slab into narrower boards, joint the edges, and glue the slab back together. But this method has its risks. If stresses exist in the slab, ripping free narrower planks could result in twisting and warping. Warping or twisting of individual planks could require face jointing and planing. Even if the method is successful, the width of the slab would be reduced by the total of the amount removed by ripping and jointing.

Long tapered maple shims could be noticeable, but without knowing more about the base and the method for attachment, it is difficult to say whether shims would be acceptable. Mortising the top to the metal base seems to me could impede wood movement and if so, could result in the top cupping or cracking.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics