Thread: How to straighten box lid - help needed!

I assume pattern side is the top? If so then there is the potential that crack/s will appear. Good luck.

This is a stand alone lid?. If this was me I would just use the simple method of getting bows/warps out of timber I have used for the last 22 years. That is,,....Wet with water the underside, (concave side), place the lid in the sun with the convex side facing the sun. The heat will pull the lid flat again. Just don't leave it too long otherwise the warp will go the other way.

Like I said, if this was me. This method has worked in most cases for me.

Good luck,

Paul

The lid appears to be a lamination of two timbers. My interpretation is that the curve is due to the two (different??) woods having significantly different shrinkage rates or are the same (or different??) wood but glued up cross grain. Having a couple of more photos showing the construction of the lid will give a better idea of what may be happening. If one board is plain sawn and the other quarter sawn they will move at different rates even if they came out of the same tree and have been seasoned identically, see below.

A standing tree contains a lot of water, when it is cut it immediately starts to loose "free water" and will stabilize at around a moisture content of 25% (the fiber saturation point). The "bound water" (the remaining water stored in the cells of the wood) is more difficult to remove and requires a process of seasoning / air or kiln drying to reduce the MC to below 15% - "seasoned wood" - for general use.

However, wood continues to move (swell or shrink) when the humidity (moisture content in the atmosphere) of its environment changes. Wood is basically hygroscopic - it will readily absorb (or lose) moisture from the atmosphere - unless it has been stabilized by impregnation with a resin or the like.

The rate of wood movement is directly related to the humidity of its environment, and the direction of the grain. It is typically very different for tangential (around the circumference - largest) shrinkage and radial (across the trunk of the tree - least) shrinkage and is almost negligible along the length (longitudinal shrinkage) of a board i.e. in the direction of the grain. That's why "cookies" cut from a log tend to look like a pie with a small slice missing when the wood dries i.e. reaches its Equilibrium Moisture Content (EMC.) This is also the reason that "bread board ends" are problematic - the cross grain boards (width) will shrink / expand more than the almost zero change in length of the long grain (length) end board/s. The position and orientation of the board in the tree determines how it will react to changes in humidity & MC, quarter sawn, rift sawn etc.

The curve in the lid is the result of differential movement, but at some point during its making it was flat. You can attempt to replicate the original conditions by modifying the environment that it is stored in. I suspect that the woods (or boards) had not been stabilized / acclimatized to their EMC before making the lid so had different moisture contents right from the start. As the wood/s "dried" their dimensions changed due to the shrinkage, and will continue to fluctuate in proportion & response to the humidity of the environment that it is in.

The presentation face being carved (more surface area and exposed end grain) means that the (carved) piece of wood will react to changes in humidity more quickly than the un-carved base.

Enjoy it for what it is - wood - alive and constantly moving. Fiddling with it unless you are a very experienced and proficient wood worker is courting trouble. Not something you want to mess with for another's treasured possession.

Boxes, doors, drawers etc are typically constructed with a "floating" panel in a frame for doors, lids & bases to avoid this issue.

Paul's solution above will work - temporarily - until the wood re-stabilizes at its EMC in its environment.

It'd probably be a good idea to have another talk with your friend and find out more detail about just when - and over what sort of time period - the lid bowed.

If the bend has been slowly increasing over decades, then there's not much that can be done, short of major surgery.

If it has only happened "since the cat knocked a vase of water onto it" then it should be possible to at least flatten the curve successfully, if not totally removing it.

Most likely, it'll be somewhere in between those two extremes.

With luck, it'll be something like "over the last couple of years" in which case wetting the underside would have more chance for success... and then getting your friend to store the box in a humidity controlled environment closer to the box's 'original' environs would go a long way to keeping it flat

Dear colleagues,

Thank you for your tips. I had another talk to the owner and it turned out that this main concern was inability to close the box rather than have lid straighten. So, with some help from mdf, shims and drum sander I have flattened the bottom side. Problem solved.

This happened to me recently from a fresh cut. I sprayed a paper towel damp not soaking wet and placed it over the cupped side. With a hot iron I went over the paper towel. Within a couple of seconds the cup was taken out. Unfortunately for me though after a day or so the piece cupped again. Even though I repeated the operation several times it kept cupping and just gave up on it. Anyway some timbers just yearn to be destined to be firewood. Hope this helps