System Stiffness

Power Drives Real Productivity

Sliding headstock lathes were developed to eliminate workpiece deflection for long thin parts, allowing deep cuts in one pass. This method of machining virtually eliminates workpiece deflection, but does not necessarily eliminate machine chatter. In a typical Swiss machining process there are a number of forces at play. The tool is pushing into the work piece and the work piece is pushing back at the tool. The harder these two forces push against each other, the pressure that is put on the spindle and all of the other machine components increases. Affected components include the ball screws, slides, and the overall machine structure. The entire system must be rigid enough to resist deflection with the machine itself. This is referred to as the Rigidity or Stiffness principle.

Main Spindle Stiffness:
For those machining difficult materials, machine stiffness is critically important to overall metal removal rates. Often buyers can become fixated on rapid traverse rates and spindle speeds while losing sight of true machining power. When building the SS20, its designers had to balance the need for high spindle rpm with the ability to take deep cuts. In the end, they settled on rotary guide bushing pictured with four angular contact bearings capable of 8,000 rpm but with the stiffness necessary to remove serious metal. Lower than average spindle rpm is more than compensated for by volumetric material removal.  Tough alloys require high stiffness.  Cutting surface speeds are typically much lower than maximum speeds.

Driven Tool Spindles
The construction of driven spindles is often overlooked by buyers. It shouldn't be. A modern Swiss machine is the equivalent of two lathes and two machines, neatly wrapped up in one productivity enhancing box. One wouldn't buy a milling machine that chattered down the street when anything more serious that aluminum was put in the vise. The SS series cross rotary spindles (pictured) feature five large contact bearings with a wide stance. As with the main spindle, your ability to remove metal quickly is the most important concern. For an excellent example of this, check out this profile of Prince Industries.