A method of producing a component part of an aircraft airframe, the method comprising: providing a first digital model, the first digital model being a digital model of the component part; producing an initial physical part using the first digital model; measuring a surface of the initial physical part; creating a second digital model using the measurements of the surface of the initial physical part, the second digital model being a digital model of the initial physical part; digitally assembling the second digital model with one or more further digital models, each of the further digital models being a digital model of a further component part of the aircraft airframe; specifying one or more fastener holes through the assembled digital models, each fastener hole through the assembled digital models comprising a first portion passing through the second digital model and a second portion passing through one of the further digital models, the first portion being aligned with the second portion; drilling one or more fastener holes in the initial physical part using the second digital model with the respective first portions of the one or more fastener holes specified therein, thereby producing the component part of an aircraft airframe; and wherein the method further comprises: using the assembled digital models, creating a digital model of a shim, the shim filling a gap between the second digital model and one or more of the further digital models; producing a physical shim part using the digital model of the shim; and attaching the physical shim to the initial physical part; and wherein the step of drilling the one or more fastener holes in the initial physical part comprises drilling one or more fastener holes in the initial physical part to which the shim has been attached. providing a first digital model, the first digital model being a digital model of the component part; producing an initial physical part using the first digital model; measuring a surface of the initial physical part; creating a second digital model using the measurements of the surface of the initial physical part, the second digital model being a digital model of the initial physical part; digitally assembling the second digital model with one or more further digital models, each of the further digital models being a digital model of a further component part of the aircraft airframe; specifying one or more fastener holes through the assembled digital models, each fastener hole through the assembled digital models comprising a first portion passing through the second digital model and a second portion passing through one of the further digital models, the first portion being aligned with the second portion; drilling one or more fastener holes in the initial physical part using the second digital model with the respective first portions of the one or more fastener holes specified therein, thereby producing the component part of an aircraft airframe; and wherein the method further comprises: using the assembled digital models, creating a digital model of a shim, the shim filling a gap between the second digital model and one or more of the further digital models; producing a physical shim part using the digital model of the shim; and attaching the physical shim to the initial physical part; and wherein the step of drilling the one or more fastener holes in the initial physical part comprises drilling one or more fastener holes in the initial physical part to which the shim has been attached. using the assembled digital models, creating a digital model of a shim, the shim filling a gap between the second digital model and one or more of the further digital models; producing a physical shim part using the digital model of the shim; and attaching the physical shim to the initial physical part; and wherein the step of drilling the one or more fastener holes in the initial physical part comprises drilling one or more fastener holes in the initial physical part to which the shim has been attached.