Flexible coupling for attaching a collet to a draw bar

A method for connecting a collet to a draw bar of a machine tool, the method comprising:

• providing a machine tool having a spindle and a pulling device;
• providing a collet adapter;
• providing a flexible coupling comprising a draw bar having a first longitudinal axis and a first coupling portion proximate a first end of the draw bar and a mounting portion proximate a second end of the draw bar, the mounting portion being configured to removably secure the draw bar to the pulling device, the first coupling portion comprising at least two elastically resilient legs spaced apart from one another, each of the at least two legs having a first coupling surface formed thereon and being configured with a radially inward bend, and a collet having a second longitudinal axis and a clamping portion proximate one end of the collet and a second coupling portion proximate a second end of the collet, the second coupling portion having a second coupling surface formed thereon, the second coupling surface being configured in a shape complementary to the first coupling surface;
• wherein the first coupling surface has a first threaded area formed thereon and the second coupling surface has a second threaded area formed thereon;
• wherein the first threaded area and the second threaded area are of a buttress thread configuration and the buttress thread configuration defines flat load bearing flanks oriented perpendicular to the first longitudinal axis and angled non-load bearing flanks oriented at an angle relative to the flat flanks, the flat flanks on the first threaded area facing axially away from the first end of the draw bar;
• and
• securing the first coupling portion of the draw bar to the second coupling portion of the collet so that the first coupling surfaces moveably engage the second coupling surfaces;
• the radially inward bends causing the angled non-load bearing flanks of the first threaded area and the second threaded area to maintain engagement with one another, thereby axially aligning the collet with the draw bar;
• positioning the collet in the collet adapter;
• positioning the mounting portion of the draw bar in the machine tool;
• securing the mounting portion to the pulling device;
• securing the collet adapter to the spindle;
• and
• applying a radial force, via the inwardly bent legs to the draw bar to concentrically seat the collet in the collet adapter such that the first longitudinal axis and the second longitudinal axis are coaxial.