Spindle head unit

Claim 1

A spindle head unit for use in a machine tool, comprising: an outer framework having a mounting space therein; a spindle extending axially in said mounting space of said outer framework, said spindle having front and rear portions, wherein said spindle includes a bore in the front portion thereof for receiving a tool therein; front bearing means for supporting the front portion of said spindle and rear bearing means for supporting the rear portion of said spindle, wherein said spindle is rotatable about the axis thereof; a drive motor for said spindle, in said mounting space, said motor including a rotor assembly rotatably fixed on said spindle and a stator assembly disposed around said rotor assembly with an annular space between said stator assembly and said outer framework, said annular space being connected to the atmosphere via air ports formed in said outer framework, wherein a gap is formed between said stator assembly and said front bearing means such that said front bearing means does not contact said stator assembly; holding means for holding said stator assembly in said mounting space, said holding means defining at least an axial through-bore having one end fluidly interconnected with said annular space in said mounting space and the other end fluidly connected to the outside of said outer framework, wherein said holding means are cantilever holding means for holding only the rear portion of said stator assembly, thereby thermally isolating said stator assembly from the front portion of said spindle; and a means for forming a stream of cooling air, wherein the stream of cooling air passes through said annular space and said axial through-bore and is then discharged to the outside of said outer framework.