August 16, 2008 – Expansion & Contraction

Our lawyer recently had a tiger maple chest made (about a year ago). He brought it to me to see if I could fix it. The original maker told him that he didn’t know how to fix it and that it must have been “bad” wood. That is just not the case.

The chest cracked across the front and back, dovetails are coming apart and the top is twisted. It is a mess!

Okay, first problem is the dovetails. They were cut at 18 degrees, extremely tight, probably required a lot of pounding and clamping to get it together. Very little glue in the joints and no finish on the interior.

The bottom was very, very tight across the grain and the battens were glued and screwed fast across the underside of the top.

Whoever built this worked their butts off and thought they were doing it correctly. They used very little glue. Fitted the bottom way too tight allowing no room for expansion or contraction. Poor guy nailed the base on with big cut nails. Here, the grain was running in the same direction so he could have just glued.

Glue battens across the top? Never. Screws in slotted holes to allow for expansion and contraction is critical.

Remember, expansion and contraction over its length is not usually an issue although highly figured/curly woods can move a little. BUT, it does move constantly across the grain. It gets wider when it expands and narrower when it contracts. Gluing the battens to the underside of the top locked it down, maybe he thought it would stop it. Well, that is not going to happen. If you lock it down it IS going to split. That simple, a 10″ wide board can move an 1/8″ over a seasonal change.

Wood absorbs moisture and releases it with humidity changes and you are not going to stop it so build with this in mind. Failure to do so will, like this chest, have your hard work turn into a shameful mess.

This builder is a good woodworker, good design, good proportion, dovetails hand cut and obviously very precise – BUT, the expansion and contraction thing – lack of an understanding wood movement has all but destroyed the piece.

I used a thin hot glue (cyanoacrylate) and flowed it into the cracks from front and back, pushed the dovetails apart and using a glue injector loaded them up with wood glue, I then re-clamped. I used a chisel and removed the battens from the underside of the top, removed the bottom and cut it a little narrower and on it goes.

Now I will strip and sand and finish everything, INSIDE and OUTSIDE. You must finish both sides and I don’t care what all of the experts say. If you don’t balance wood, it will move adversely, it will absorb more moisture from one side than the other. I really don’t see how so many people insist that it isn’t necessary, IT IS!

I hate this kind of work. What bothers me most when I run into something like this is that the original builder hasn’t bothered to find out what went wrong but rather insisted that it wasn’t his fault. They have had to experienced these issues with other pieces.

Whenever you have something go wrong with a piece, don’t just toss it aside and say oh well, you need to find out more about why there was a problem. Ya know, doing the same thing over and over again and expecting a different result is the definition of …………………

Catch ya Later!

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One Response to August 16, 2008 – Expansion & Contraction

  1. Denis says:

    great entry! understanding expansion and contraction is one thing that i thing separates the pro’s from the beginners. like in my trash can thing, for the raised panel i made sure to float it by 1/8′ all around to allow for expansion and contraction of the panel and the rails and stiles which can’t be forgotten about. its just one thing that if you are building fine furniture needs to be taken into consideration in every aspect of your piece.

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