I'm curious about how mortise and tenon joints hold up despite wood movement. When wood expands along its grain, I'd expect the legs of a table, for instance, to either pull away from the apron or push into it, causing stress. So, why don't tables fail at the points where the legs meet the aprons or rails? I get that wood moves across the grain, but that basic rule doesn't explain how mortise and tenon joints can account for wood movement and stay intact. Any insights?
3 Answers
To help the joints cope with movement, it's common to build everything so that the wood moves in similar directions. Think of a ladder—the steps might expand or contract, but since they're oriented the same way, the entire structure holds up fine. For tables, using methods like z-clips allows the top to move independently from the apron, which is smart since the apron can change size without affecting the top.
Modern adhesives play a big role in joint stability. In older constructions where glue wasn't as reliable, they relied more on mechanical fixes like wedged or pegged tenons. Today’s mortise and tenon designs account for a bit of wood movement, allowing parts to shift without compromising the overall stability of the furniture.
Wood movement is a lot more complex than just saying it moves across the grain. A key factor is the glue used in these joints, which provides a lot of flexibility and strength. Essentially, the movement of the wood at the joint isn’t strong enough to overcome the adhesive's hold. If you make your tenon too wide or too narrow, you could run into problems, but overall, the glue keeps everything secure even as the wood expands or contracts.
Exactly! The glue's flexibility really matters. Smaller widths mean smaller movements, so it's all about finding that right balance.