Spline too-wide dadoes for a snug fit

Sometimes, even with your best efforts at accuracy, creating snug-fitting joinery can be difficult. Take a dadoed shelf joint for example: You painstakingly measure the thickness of the plywood shelf, carefully adjust your dado blades to that thickness, and voila! the dado you cut is too wide, and the shelf fits loosely, revealing a gap. Another piece for the scrap bin? Not so fast--here's a nifty solution aimed at fixing your ill-fitting joint.

1. Start by routing a 1/8"-wide x 1/2"-deep slot down the center of the shelf end. For best results, we used a slot-cutter bit. Measure the exact width of the slot.

2. Make the spline from a 1/2"-thick piece of solid wood. Ideally, the thicker end of the spline should be about 1/16" thicker than the slot itself. Tilt your sawblade 5° . Now rip the edge to form the first bevel, below, left. Next, flip your stock end-for-end, reset your fence to achieve the desired thickness, and make the second pass, ripping the spline free. Dry-fit the spline in the shelf groove. (To remove it, tap the spline out one end of the slot.) If it makes the shelf end too thick, just sand the spline a little.

3. Once you're satisfied with the fit and feel it thickens the shelf end enough, apply glue to the slot. Tap the beveled spline into place, seating it fully. Then cut off and sand any protruding spline at each end.