Assembling pieces without glue allows you to check the fit of joints and avoid potential splits at glue-up. Tenons too tight in their mortises can cause splits.

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DryFitAssemlies

Assembling pieces without glue allows you to check the fit of joints and avoid potential splits at glue-up. Tenons too tight in their mortises can cause splits, as shown. A good mortise-and-tenon joint should go together easily by hand, but not be loose enough to fall apart. Avoid too-thin mortise walls, which split easily, by never making them less than 14 " thick. You also can divide your workpiece thickness into thirds, creating two mortise walls and one tenon of equal thicknesses. Trim tenons so they slide into mortises snugly. This tenon was too thick, causing the thin mortise wall to split.