Riten Industries, Inc. Provides Machining Solution for SIC
Southern Illinois Crankshaft Inc., Red Bud, Ill., machines billet crankshafts for oil-industry pumps and high-performance diesel engines, including ones used in tractorpull
competitions. SIC processes the parts in a twin-spindle Okuma MacTurn 550-W multifunction turning center. The machine has a W-axis, or live spindle, where the tailstock would be on a single-spindle lathe. President Michael Schaefer said, "We are basically turning the Okuma into a tailstock machine:'
Until recently, SIC supported the part end opposite the chuck with a dead
center clamped in the W-axis spindle. The spindle's servomotor generated
the axial pressure needed to hold the part securely during machining. But
variations in stock length, as well as thermally induced changes in part size
during machining, often changed the axial load. Too much axial pressure can cause a part to bind and eventually shut down the machine; insufficient pressure allows a part to move during machining.
The variety and volume of SIC's work were also considerations. The
crankshaft stock varies in size from about 2" in diameter and 24" long
to 12" in diameter and more than 70" long. Part volume isn't high. Handling small lots effectively requires quick changeovers, but using the machine's servo to adjust the axial load for the different-size parts consumed too much time.
Seeking to make the axial pressure more consistent, SIC conferred
with Riten Industries Inc., Washington Court House, Ohio, a manufacturer of live centers, dead centers, face drivers and custom work holding. Riten offers standard
products, as well as application-specific workholding solutions. According
to Travis Horton, Riten Vice President of Sales, "Half our business is special
work holding."
In response to SIC's inquiry, Riten produced a linear-compensating live
center designed to be clamped in the chuck of the W-axis spindle. The device
consists of a straight-shank live center that fits into a cylindrical housing
against a spring. An access plug at the rear of the housing enables the
spring to be easily changed. Riten included four different springs, color coded
to identify their deflection rates. The system provides 0.500" of travel.
When a part is put in the machine, it's set up with 0.250" of preload, making
0.250" of compensation available.
Dale McMillian, Riten's Director of R&D, said a compensating center enables a shop to locate a part in a machine according to-the stock length specified in the print. "Should the
stock be long or short or be subject to thermal elongation, the center still
provides sufficient axial load to do the machining operations and not impose
a load on the servo or overload the ballscrew," he said.
McMillian said cutting parameters and part weight determine the appropriate spring. He added that Riten's relationships with spring makers facilitate obtaining springs
to match applications that fall between the ranges of the springs Riten provides.
