Building a coffee table and assembling the pieces for the skirt pictured here. I always use painters tape so I can see my marks for my line up and I make oversize mortises in one side of the joinery, the longer stretchers here. I even mark the tape with a felt pin 'X' so I know where the mortise is going. Review my set up before proceeding. In this example I had my fence at 90 degrees. Using a 5mm mortise bit.

I referenced the long stretcher off the outside face and put the mortises in the ends of those two boards. So the center line is down from the bottom of the fence to the center line of the bit.

The shorter stretchers overlap and hide the end grain on the longer stretchers, so the mortise goes on the inside of the board. the end of this shorter board should line up with the outside face of the longer board. I clamp the work to my table. The shorter end pieces I held the Domino vertically referencing off the end of the board with the bottom of my fence and put the mortise in the inside face. The end of this shorter board should be the same reference point as the face of the longer stretcher.

My problem...The end shorter boards hung over the longer boards by @ 1/32" when dry assembled. I don't understand because i think I was referencing off the same point and the depth of the mortise should have been the same allowing the joint to be flush, but it wasn't. I fixed it by making my mortise int he shorter boards a little more shallow and it came out fine, but....

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