More Sliding Head Automatics

While visiting a U.K. honing machine maker about 6 years ago, we were looking at the factory's machine shop. Turning was a big requirement, and the manager was considering buying a new CNC lathe.

He liked the idea of being able to do all the parts on one machine. The bulk of components fell readily into the category of the standard two-three axis CNC light-to-medium bar automatic, with maybe some cross-drilling and face and slot milling.

That left about 15 percent of the parts that still had to be turned on a manual or programmable toolroom lathe or be outsourced. What he would have liked was a CNC sliding head automatic. In his view, that would leave only about 35 percent of the parts that were "too short" to be easily machined on a sliding head machine.

Today, I could point that manager toward a number of manufacturers such as Tsugami-Mori, Japan, or Gital, Italy. They noted the limits of traditional sliding head designs and found a new approach to machine tool layouts.

The results are CNC sliding-head automatics that can cut short or long parts from bar without any problems. The sliding-head automatic is noted for high precision. Reliable and sustainable precision is what manufacturers of turned components need to satisfy ever tighter tolerances.

A double spindle arrangement on the Tsugami-Mori BS 20/26/32 (6-32 mm bar) CNC sliding head automatic lathes is designed to meet the demand for higher working precision. The rotary guide bush assembly and main spindle are integrated and synchronized in operation.

Tsugami-Mori says this design results in higher accuracy plus heavy duty machining capabilities. This design also is said to offer low noise and vibration characteristics for better surface finishes compared with the traditional arrangement of machining spindles.

The double spindle increases efficiency by three times. The BS series machines can take larger cuts with greater accuracy. The reason is that the bearing load capacity is three times greater and the bearing span three times wider compared to traditional sliding-head construction.

Depending upon material, Tsugami-Mori says its sliding head machines will maintain dimensional tolerances of 8.0 mm, roundness of 1.5 mm and surface finish 1.5 mm Ra.

In the design of the sliding headstock and cartridge bush carrier, the collet's front face can approach right up to the rear of the guide bush, allowing very short components to be machined.

Gital has taken a different approach. The Gital GLD 20 mm and 25/32 mm modular CNC bar automatics can perform sliding head work with a turning length of up to 900 mm. The GLD 25, for example, can be equipped as a simple three-axis gang-tooled automatic, a four-axis version with sliding tailstock containing a synchronized subspindle or a five-axis configuration with a seven-tool turret containing a live subspindle.

In the latter two configurations, the subspindle also acts as workpiece support when machining long, small diameter parts. Instead of a collet or work gripper, the subspindle chuck supports a rotary guide bush and can be programmed to precede the turning tool along the programmed turning path. With such an arrangement, Gital says the machine will handle sliding head work. Components up to 900 mm long can be turned, milled, drilled and bored in the GLD 25.

Both makes of machine perform a wide variety of back-end machining work while, simultaneously, work can begin on the bar in the main spindle.

Today it is wise to review CNC sliding head automatics in a different light, and pay attention to increasing job changeovers and pre-set tooling.

The cost of a CNC sliding-head automatic should be judged by comparing changeover times to the cam machines. Faster changeovers mean faster response and lower stocks.