I'm curious about the conventional wisdom on how wood movement affects tenons and joints. Specifically, if a tenon expands and is a tight fit, can we assume that the mortised piece will expand at a similar rate—especially if they are both made of the same wood type? Should I be concerned about a tight-fitting tenon splitting the mortised piece over time with seasonal changes? Thanks for the insights!
1 Answer
Generally speaking, unless you're working with large timber frames, you shouldn't worry too much about tenon fit causing problems under normal conditions. Wood movement primarily happens across the grain, and the wider the wood, the more it moves. As a rough guideline, a foot-wide plain sawn hardwood board might move about 1/4 inch with the seasons, while a narrower tenon would only shift about a hundredth of an inch. That means a snug fit isn't a dealbreaker, but it shouldn’t be so tight that you have to force it into place.
Thanks for clarifying! That makes a lot of sense. If the movement is minimal, do you think it's safe to hammer a tenon into its mortise without worrying about future splitting?