Reprinted from Modern Machine Shop, January 1997

While most of the manufacturing world is embracing Just-In-Time manufacturing methods to eliminate storage inventory, Lovejoy Inc., Downers Grove, Illinois, retains a fairly large inventory on some of its products in order to provide extraordinarily quick deliveries to its customers. This has helped the company retain a leadership position in a very competitive worldwide market. Lovejoy produces a complete range of power transmission couplings, and typically ships around 100,000 couplings per week.

A significant part of this business involves couplings where the shaft bore sizes vary as specified on the customer's order. Accordingly, each coupling must be bored after the order is received. Rather than process the entire coupling after the order is received (which would take several days), Lovejoy machines the entire coupling with the exception of the shaft bore and stores them on the shelf. This procedure allows shipping a coupling in far less time from receipt of order, often in 24 hours, which gives Lovejoy a competitive advantage.

When an order is received, a nearly complete coupling is pulled out of stock, a lathe is setup for the shaft boring operation, and the coupling is ready to ship in a matter of a few hours. However, each different order involves a chuck jaw changeover, which places a high priority on chuck performance. Using previous conventional chucking practice, a changeover would normally take 10 minutes. Since the coupling shaft boring requires the use of soft-jaws that clamp on finish-turned OD's, soft-jaws would have to be removed, new soft-jaws mounted, and a light cut taken to true-up the clamping diameter, because the remounted jaws would not repeat close enough to eliminate the need to rebore them.

This reboring was necessary in spite of the fact that each set of soft-jaws was dedicated to one coupling OD size. After considerable investigation, Lovejoy settled on the purchase of SMW Ultimate CNC Chucks, which they eventually mounted on seven of their CNC lathes. Mark Caccippio, plant superintendent relates: "We were looking for fast-changeover features, but we also wanted a chuck with enough rigidity to allow us to do our rough turning at high stock removal rates we don't believe in babying our machines. The SMW chucks offered both advantages and have provided excellent results." Changing jaws on SMW chucks is described as simplicity itself. A hex key is inserted into a socket in the chuck body.

Turning the key in the clockwise direction disengages the jaw from the actuating mechanism allowing the operator to slide the jaw out of the guideway. The new jaw is then inserted and positioned. Turning the hex key counterclockwise engages the new jaw with the actuating mechanism. Changing a set of three jaws takes less than one minute. Adjusting or reversing jaws is likewise accomplished in less than one minute. An important exclusive safety feature of this chuck helps prevent loose-jaw accidents. Once the hex key is rotated clockwise to release the jaw, the key cannot be removed from the chuck body until the key is rotated counterclockwise to its original insertion position. T

he counterclockwise rotation insures that the new jaw is engaged with the actuating mechanism. Once the key is removed and the spindle starts rotating, there is no danger of a loose jaw being propelled out of the chuck body by centrifugal force causing potential harm to the operator or damage to equipment. The major advantage of the SMW Ultimate CNC chuck in Lovejoy's situation is its ability to eliminate the need to rebore remounted soft jaws. The accuracy of the jaw mounting mechanism insures that remounted jaws will repeat within 0.0002-inch TIR. This level of jaw position accuracy permits holding coupling bores to 0.0005-inch concentricity to the clamping diameter without reboring the soft jaws. Eliminating reboring plus the quick jaw change reduces total machine changeover downtime to 10 minutes or less. The chucks rigid design is demonstrated by its flat grip-force curve. The grip force curve is a measure of the stiffness and structural integrity of the chuck. Asrotating speed increases, many chucks lose a significant amount of grip force due to deflections in the chuck body caused by centrifugal force.

To avoid workpiece slipping in the jaws, the work must be overclamped which can cause distortion, or, the machine speed and feed rates must be slowed down, which increases piece-cost. Other advantages offered by the chuck include the ability to apply two different grip forces in the same machining cycle without releasing the workpiece. Thus, roughing and finishing can occur in the same cycle without rechucking.

The chuck can also be provided with master jaws that allow using wide jaw designs popular on conventional chucks, thereby enabling use of existing jaw inventories. The good news for companies that are not now using this type of chuck is that the chuck can be retrofitted to existing lathes in about four hours, and it is available on nearly all new lathes.

Buckley Owens Machinery Corp. 6416 Fly Road | East Syracuse, New York 13057 Telephone 315.432.0708 Fax 315.432.0736 Email: info@buckleyowens.com