A twin-turret approach to machine tool stiffness, stability

Two rotary axes beat 2′ of stacked linear axes. That’s the idea behind the new Twin Turret Generator (TTG) machine tools from Cranfield Precision. According to the company, the TTG machine offers a stiff and thermally stable design that improves machining precision and repeatability.

While conventional machine tools mainly use stacked linear axes to control motion, the TTG’s patented “twin-turret” design employs two stiff rotary axes and a short linear infeed axis to produce relative motion between the cutting tool and workpiece.

The TTG design from Cranfield Precision coordinates the motion of two rotary axes and a short linear axis for high-precision machining. Image courtesy Cranfield Precision.

To explain key differences between the TTG and conventional machines, Mark Stocker, Cranfield’s division manager for grinding, uses the concept of the stiffness and thermal “loop,” which refers to the path leading from the tool to the base of the machine and then back to the component being machined. “The longer that path is, and the more axes it runs through, the less stiff the loop will be,” Stocker said.