It is important to understand that wood reacts to humidity changes not to temperature changes.
Metal, on the contrary, reacts to temperature changes and is unaffected by humidity changes. Since many woodwinds include both, this can cause problems.
Whenever the humidity changes so will the wood. Higher humidity makes the wood swell and expand, dryer conditions make it shrink. To be able to build a well-functioning woodwind instrument, the wood needs to be dried to about 6% humidity. This will give the wood its smallest physical dimensions. Now a mechanism can be mounted onto the joints, otherwise the posts screwed into the wood would crack the wood as it shrinks. During cold dry winters or in dry hot summers the result is similar. It is best to keep your instrument inside a temperature-controlled home, and never leave it inside of the car when you are gone. Typically all cracks on posts and the register tube are dry cracks.
Dont get the instrument pinned under any circumstances!!! (Read also: Crack pinning )