Sheffield Tony":1xxapnz0 said:
... all the articles I Googled, and the one above, suggest that wood shrinks in winter and expands in summer. This is quite contrary to my experience - I notice that most of the articles I were American; is it their climate ?
I admit I can't quite puzzle out the relevance of wood movement caused by changes in in relative humidity (RH) leading to the handle of your plane parting from the body, but I may be able to shed some light on wood movement.
Here in the UK, dry wood, i.e., wood at 20% MC or below, loses moisture during the summer and gains moisture during winter if kept in sheltered locations exposed to the elements, e.g., open sided sheds, barns, etc, and the wood tends to hover between roughly 17- 20% MC. Externally, relative humidity (RH) is typically lower during summer than winter, and RH is the primary factor determining wood MC, assuming the wood is not soaked by water, e.g., rain, snow, submerging in water, etc.
Conversely, the RH situation in houses and other habitable buildings is usually the reverse of external RH seasonal fluctuations. Typically, but not always, habitable buildings show lower atmospheric RH numbers in winter than summer, so wood tends to shrink during winter and expand during summer. The reason for this is cold, winter air cannot hold as much actual water vapour as warmer summer air, and the generally limited air entering a house during winter is usually heated, thus lowering RH further. In the summer, people open windows and doors to help keep cool, and this lets air in. Typically, RH in such buildings fluctuates between about 40% RH in winter (admittedly on the low side, and largely affected by the building's structure, its insulation, the glazing, etc) and about 65% in the summer. Typically, wood tends to range between about 8 - 9% MC (winter) up to 11% - 13% MC (summer).
Below are some other typical numbers.
15-19% wood MC. Buildings with poor insulation, single glazing, minimal or no heating, et cetera, e.g., sheds, rarely heated workshops, churches, et cetera.
10-14% wood MC. Buildings with intermittent heating providing room temperatures between 12- 21ºC (54ºF- 70ºF).
6- 8% wood MC. Buildings and rooms kept very warm (21ºC+ [or 70ºF+]) e.g., hospitals, storage facilities, museums, or wood used near radiators, fires, south facing sun rooms, et cetera.
All of the above need qualification with caveats. For example, the western side of the British Isles is generally wetter than the eastern side, north is colder and damper than the south, insulation and climate control systems vary significantly from one habitable building to another, e.g., an old, stone built country house is likely to have quite a different internal seasonal micro-climate to a modern house incorporating the latest climate control technology. Slainte.
