An assembly for a cartridge needle insertion mechanism comprising a housing, a cartridge needle defining a cartridge needle axis and a cartridge closed by a septum. Furthermore a cartridge needle slider being linearly guided by the housing along an insertion axis to be moved by a driver from a first position, where the cartridge needle is not penetrating the septum, to a second position where the cartridge needle penetrates the septum of the cartridge. A cartridge needle holder holding the cartridge needle is operatively coupled with the cartridge needle slider to be moved with the cartridge needle slider from the first to the second position. The assembly has a compliant coupling between the cartridge needle holder and the cartridge needle slider configured to facilitate movement of the cartridge needle holder with respect to the slider when moved into the second position, thereby compensating for needle penetration forces.
