【木組み】＃11－4/7 四方蟻継ぎ男木Japanese wood craft.Processing of the lower side of the four-way dovetail joint.

You can see the production process from #11-1.　See #11-2 for a detailed explanation. The point is to make the dimensions of the machined upper bottom surface the same as the upper surface to be machined this time.
細かい説明は＃11－2を見てください。ポイントは加工した女木の底面の寸法と男木の上面を同寸にすることです。