Abstract: In a method of assembling a freeze dryer shelf having opposed, parallel first and second plates spaced apart from one another, and a plurality of ribs defining at least one flow channel for conveying a diathermic fluid between the first and second plates, the ribs are first located against the first plate and secured to the first plate. The second plate is then located against the ribs, and the ribs are secured to the second plate by, for each rib, inserting a welding torch between the first and second plates and adjacent the rib, and moving the welding torch along a joint between the rib and the second plate to weld together the rib and the second plate.