MBW “Shorts” – Wood Movement and the Simple Wooden Box

August 20, 2013

Shortly after the release of the most recent video featuring the new photo boxes I’m making for my wife’s business I received an email from an audience member asking if I was concerned about the expansion and contraction of the box’s bottom panel effecting the metered corners of its sides?

miter corner of simple wooden box

miter corner of simple wooden box

In truth, not really, or at least not nearly as much as I would be if this was a different project and with larger dimensions and maybe even different materials. Of course, it’s not just the dimensions and materials that make confident against the wood movement having drastic effects on the boxes, there’s also a few other things too that make me feel confident about my decision.

In today’s video I discuss these topics in the hopes that I answer the audience member’s concerns and maybe some others from folks who were thinking along the same lines.

Items mentioned in today’s post:

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Comments (2)

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  1. Jeffrey says:

    I always thought moisture was the force behind wood movement and temp was almost irrelevant yet you seem to indicate the opposite. Is there a general rule covering this?

    • Matt says:

      Hi Jeffrey,

      Sorry for any confusion regarding wood movement. Moisture content is the driving force behind wood movement. When moisture content goes up, wood expands. Moisture content goes down, wood contracts.

      I tried to explain more about this in my video on winter woodworking, you can check it out at http://mattsbasementworkshop.com/503-winter-woodworking-tips/

      But as a general rule for myself, the time of year that I’m building my projects will almost always dictate how much room for expansion and contraction I’ll allow in a project.

      In the summer when the temperature is highest, the air can hold onto much more moisture and for a longer period of time. Because properly dried wood is drier than the surrounding air, the moisture will move from where it’s abundant (the air) to where it’s not (the wood). This will cause the expansion.

      In the winter the cold air doesn’t hold moisture very well and is often drier than the wood so it will do the opposite and pull moisture from the wood thus causing contraction.

      This is true even though in a state like Michigan our overall rate of humidity doesn’t change dramatically year round. And as I mentioned in the video, given the fact our houses are far more environmentally controlled than ever (temp and humidity), it’s becoming less of an issue there also.

      The good news for woodworkers is that if you have properly dried lumber (kiln or air-dried) and it’s acclimated to your region, regardless of daily or even seasonal changes in humidity it should only move a few degrees (% moisture content) in one direction or another. So it can be predictable and you can build in allowances for that expansion and contraction.

      I hope this helps.

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