Machining description for a CNC machining process has the purpose to give information about the machining process and relations between, product, process and resources. Currently used information model requires time consuming and expensive procedures during the manufacturing preparation process to create this documentation. This paper presents how machining descriptions can be generated more efficient. We have studied how ISO 10303 standard for product data representation and exchange, known as STEP, can be utilized in the manufacturing preparation process. We present how information requirements for machining descriptions containing a relationship between a machined face, its tolerances and used cutting tool can be met. To demonstrate our research result we have developed a prototype system where STEP data models of the machiningprocess, workpiece with tolerances, fixture and cutting tools are used and integrated. We have proven that information separation of data, to create machining descriptions for CNC machining, is currently done unnecessarily early in the manufacturing preparation process.