Tool holder coupling apparatus

A tool holder coupling apparatus comprising:

• a tool holder comprising a flange, a support section and a pull stud bolt, said support section having a tapered surface portion extending from a large diameter end to a small diameter end, a rigid, straight cylindrical portion of fixed diameter extending from the pull stud bolt toward the tapered surface portion and a relief portion contiguous with and connecting the tapered surface portion and the straight cylindrical portion, said tapered surface portion, said straight cylindrical portion and said relief portion being integrally formed as a single piece construction;
• and
• a machine spindle having a front end face and a central cavity for receiving said tool holder and including:
• an open distal end section having a first interior surface portion defining a first portion of said central cavity and having a taper corresponding to the taper of the tapered surface portion of the tool holder;
• a straight section having a straight cylindrical second interior surface portion corresponding to and slidably engaging the straight cylindrical surface portion of the tool holder and defining a second portion of said central cavity;
• and
• a middle section connecting said distal end section and said straight section, said middle section having a third interior surface portion defining a third portion of said central cavity, said third interior surface portion being spaced from said relief portion over the entire axial length of said relief portion with said tapered surface portion of said tool holder fully seated within said first interior surface portion of said machine spindle, wherein said tool holder, fully seated in said central cavity of said machine spindle, has a rear end face of said flange spaced from said front end face of said machine spindle and wherein said tool holder slides with respect to said machine spindle as speed of rotation of the machine spindle increases.