I have a DeWalt Biscuit Joiner that I use to make boxes or cabinets. That is 2 sides and a top and bottom. The fence for the joiner is set at a height of 3/8" and is is down, or parallel to the blade. I am using 3/4" plywood. My method is to place the top and bottom pieces on a flat surface with their inside faces up. I have one end of a piece overhanging whatever surface the piece is on. The other end is clamped to the work surface. I then place the joiner wherever I have made a mark and position it so the fence is pressed against the end edge. The slot is then made into the inside face, parrallel to the end edge. The distance from the end edge is the same as the distance of the fence from the blade. I now lay the side pieces down with their outside faces up. I place the fence of the joiner on the outside face and hold it there. The joiner is pushed against the end edge of the side and the slot is cut. I then place the biscuits and glue and clamp the pieces together.
My problem is that when the glue is dry the top and bottom pieces overhang the side pieces by about 1/16". This happens at all 4 joints and has happened on several cases I have built.
Can anyone tell me what I am doing wrong? I use a router with a flush trim bit to correct things but I would like to avoid having to do that.
Thanks for any and all help.