Adaptive guide bush for Citizen sliding-heads

The system will accommodate any tolerance variation on the outside diameter of the cheaper material, while allowing the normal machining speeds and feeds, consistent accuracy and high concentricity levels to be maintained on components. Available on all new Citizen machines supplied through Citizen Machinery UK of Watford, the AGB system replaces the standard rotary guide bushing, which, because its operating diameter is fixed, requires the use of close tolerance ground material when strict size and geometric tolerances have to be maintained. The problem with more standard material, such as bright bar, are the wider tolerance limits of the rolled material that permits the outside diameter to fluctuate in size from bar to bar. On all sliding-head machines, the standard rotary guide bush uses a single taper to provide the mechanical actuation that can mean the length of the bearing surface of the bush to support the bar is normally restricted to between 15 and 19 mm. It also creates a non-parallel closing action for the bush, so if the barstock is on minimum tolerance, it is only gripped by the front of the collet. This effect can also cause the headstock collet to lose position and have a detrimental influence on the surface finish of the part. If however, the material is close to its top limit, the gripping action of the collet is only applied to its back end. Further problems can also emerge when machining titanium, for instance, or gummy materials such as certain stainless steels, when the sliding-head machining process attempts to draw the bar back into the guide bush. The Citizen AGB has the advantage of a double taper ,which initiates a more positive parallel closing action along its material support length of 50 mm - up to three times longer than is achieved with the single taper. As a result, constant pressure is applied around the bar material and, due to its positive action, the bushing is able to accommodate material with a size variance between ± 0.1 mm on diameter. Also, because the Citizen AGB always maintains a constant pressure, the bar material will remain on the machine centre line meaning run-out is minimised enabling tighter concentricity to be maintained during the cutting process.