Take a look at the pictures from this post: Box Joints and Dovetails - #33 by MikeH
The stretcher does “obstruct” the opening a little. I placed a hinged fixture above it for a couple of reasons:
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I can square it up to the X-axis (2 reference boards make it easy to line up again).
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The Z-axis can be squared up as well - I adjust at the bottom as necessary.
Overall, I’m happy with how it’s working. I’ve had to adjust my CAM approach a little, I’ve had more success not relying on measuring the width of my board perfectly - my tablesaw isn’t as precise as my CNC, and flipping a board around doubles up on any very small error. So, I make sure to always “start at the bottom” of a box for a cut, instead of some cuts starting at the other side.