The purpose of a Lumbermill is to convert medium wood into planks. To convert the item 'Med Wood' into the item 'Plank', you must place it in the slot at the tower-like top of the Lumbermill. The Lumbermill provides two planks for every piece of medium wood converted. Sometimes the Lumbermill may glitch, converting the wood into four planks which may clog it. Planks are mainly for furniture and walls.
The recipe for this building is similar to that of the other useful buildings.