A Different Way To Turn

Typical parts produced by Escomatic machines are shown

The heart of the Esco concept is the cutter head. This head, shown above with four toolholders, revolves around stationary coil or barstock. The cutters are fed over a short travel distance using cams or CNC servo to control the tool stroke.

For material up to 6 mm, a rotating straightener is used to take the kinks out of the coil stock. The coil passes through five bushings. The center busing is adjustable and cambers the wire as the unit rotates. Axial travel of the unit is 80 mm and imparts the third direction of movement on the material during the return stroke after cut off. Profiled material can be straightened using special jaws in the bushings.

During a recent visit to the Esco plant in Switzerland, I was told there are upwards of 3,500 Esco machines installed in the North American market. Since the beginning of 2005, Tornos Technologies (Brookfield, Connecticut) is responsible for service, sales and application functions for existing machines and new Escomatic equipment. “Esco compliments our Deco line of single-spindle machines,” says Tornos President Tom Dierks. “Esco’s niche is small diameter, coil-fed production, which dovetails nicely into the range of Deco single-spindle machines.”

The basic anatomy of the Esco machine consists of: 1) counter collet for cut-off support; 2) rotating tool head; 3) feed rollers; 4) straightening unit; and 5) Fanuc NC control. On this cam model, the speed of the main shaft is programmable. More complex machine models can progressively process three parts simultaneously using up to 11 axes of motion under full CNC.

The tool head can present two, three or four tools to the stationary workpiece. As this unit rotates around the work, movement of the colars in the center of the shaft actuates the toolholders. Cams or CNC servos generate this movement. Photos courtesy of Miles Free

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Back in the late 1940s, Willy Rosetti, a Swiss parts maker, had a problem with a burr on a watch part he was attempting to produce. Conventional radial-fed cut-off tools generated the burr that subsequently had to be filed.

To address this problem, Willy came up with a new turning idea we now call the Esco concept, which evolved into the Escomatic machine tool line. About 50 years later, more than 10,500 installed machines give testimony to the viability of the concept.

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The Esco concept turns turning 180 degrees. Unlike conventional lathes, the material, which is coil stock or bar from 0.02 mm to 12 mm, does not rotate. Stationary stock allows the use of round and profiled material.

The stock is held in place by a feed roller and guide bushing arrangement, while a rotating tool head removes metal. As the head spins, two, three or four cutters feed into the stationary material creating the designed part geometry.

Actuation of these cutters is by cams or CNC servomotors. Depending on the machine model, maximum head rotational speeds run from 8,000 rpm to 12,000 rpm. To overcome the significant centrifugal force generated at these speeds, the toolholders pivot into the stock through an arc rather than a straight radial feed motion. In another nod to centrifugal force, the cutters are set very close to the stock. A production benefit is that such short tool travel reduces non-cutting time.

For material up to 6 mm in diameter, it is necessary to straighten the incoming coil before it is fed into the rollers and guide bushing. A rotating straightener is standard on the Esco machine line. It revolves around the stock, cambering and straightening the wire by a combination of three movements applied to the stock. For material from 6 mm to 9 mm in diameter, a roller straightener is available.

After the machining cycle is complete, a counter collet supports the machined parts for cut off. Supporting the machined part during this operation produces a flat clean end eliminating the pip (unwanted material often created by conventional cut-off operations).

All of the machines in the Escomatic line employ the Esco concept for production turning of components. The line diverges when it comes to backworking, drilling and other additional operations needed for more complex parts in a single handling. Here, the goal is to match machine capability with the requirements of varyingly complex applications to achieve high speed, high volume production of complete machined parts.

— Tornos Technologies U.S. Corporation