A 3D printing apparatus comprising: a supply module to receive build material from a build material store; a build material distribution element within a base portion of the supply module to distribute build material within the supply module; a blade rotatable about an axis substantially level with the top of the supply module to move build material in the supply module above the top of the supply module; a spreader for spreading build material moved by the blade above the top of the supply module over a support platform and a controller to: control the deposition of build material in the supply module from the build material store; control the build material distribution element to distribute build material along the length of the supply module; control the blade to move to a pre-feed position such that a portion of the deposited build material in the supply module is moved above the top of the supply module; control the spreader to move in a first direction to push the portion of build material above the top of the supply module into the base portion of the supply module to leave a predetermined dose of build material on the blade; control the blade to move to a substantially horizontal feed position at which the predetermined dose of build material is positioned level with the top of the supply module 102; and control the spreader to move in a second direction opposite the first direction to form, using the predetermined dose of build material on the blade, a layer of build material on a support platform. a supply module to receive build material from a build material store; a build material distribution element within a base portion of the supply module to distribute build material within the supply module; a blade rotatable about an axis substantially level with the top of the supply module to move build material in the supply module above the top of the supply module; a spreader for spreading build material moved by the blade above the top of the supply module over a support platform and a controller to: control the deposition of build material in the supply module from the build material store; control the build material distribution element to distribute build material along the length of the supply module; control the blade to move to a pre-feed position such that a portion of the deposited build material in the supply module is moved above the top of the supply module; control the spreader to move in a first direction to push the portion of build material above the top of the supply module into the base portion of the supply module to leave a predetermined dose of build material on the blade; control the blade to move to a substantially horizontal feed position at which the predetermined dose of build material is positioned level with the top of the supply module 102; and control the spreader to move in a second direction opposite the first direction to form, using the predetermined dose of build material on the blade, a layer of build material on a support platform. control the deposition of build material in the supply module from the build material store; control the build material distribution element to distribute build material along the length of the supply module; control the blade to move to a pre-feed position such that a portion of the deposited build material in the supply module is moved above the top of the supply module; control the spreader to move in a first direction to push the portion of build material above the top of the supply module into the base portion of the supply module to leave a predetermined dose of build material on the blade; control the blade to move to a substantially horizontal feed position at which the predetermined dose of build material is positioned level with the top of the supply module 102; and control the spreader to move in a second direction opposite the first direction to form, using the predetermined dose of build material on the blade, a layer of build material on a support platform.