Note the edge and end milling. We call this "Center Match" on the sides and "Square End Match" on the ends.
This is a nice tight fit. It's not easy to do with rough lumber.
This is a big White Pine tree on the shores of Wolf Lake that snapped off in a windstorm 10 years ago. We first considered harvesting it as a perfectly healthy tree 20 years ago when we logged in that area, but we decided to leave it. It's a shame to have lost it, but we've recovered some great product from it now.