roger lance
From above, you say the splines are loose....you want snug....not tight....not loose....if you try this method....again, my advise is to glue the spline into one side only....let the glue dry....then proceed with the final glue-up....glue control is a rarely discussed topic and most of us were taught incorrectly by Norm to use too much glue with glue coming out of a joint only to be wiped away with a wet rag....excessive glue is of no benefit to the joint....getting the right amount of glue on the right surface makes for strong joints and minimal mess....make some test pieces with dado, spline, and mitered sides and see how this will work. In addition, I would remind you of a mortice/tenon technique where material is removed from the shoulder of the tenon to insure that the edge of the tenon shoulder makes perfect contact with the side of the mortice board....you get visually a real tight appearance of the final joint with this technique.....some of the material of the mitered edge could also be pared back toward the spline/dado with the edge of the miters now going together tightly.