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Citizen offers adaptive guide bush for CNC lathes

A Citizen Machinery UK product story
Edited by the Engineeringtalk editorial team Sep 28, 2009

Citizen has developed an adaptive guide bushing (AGB) solution, which is intended to enable the use of a cheaper bright bar instead of the normal ground or specially prepared bar material.

The AGB solution is available on the company's range of CNC sliding-head lathes.

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 of its operating diameter, is fixed and requires the use of close-tolerance ground material when strict size and geometric tolerances have to be maintained.

The problem with more standard bright bar material is the wider tolerance limits of the rolled material, which permits the outside diameter to fluctuate in size from bar to bar, according to the company.

On all sliding-head machines, the standard rotary guide bush uses a single taper to provide the mechanical actuation, meaning that the length of the bearing surface of the bush to support the bar is normally restricted to between 15mm and 19mm.

It also creates a non-parallel closing action for the bush, meaning that 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 a double taper that initiates a more positive parallel closing action along its material support length of 50mm, which is up to three times longer than is achieved with the single taper.

As a result, constant pressure is applied around the bar material and, as a result of its positive action, the bushing is able to accommodate material with a size variance of +/-0.1mm in diameter.

Since the Citizen AGB always maintains a constant pressure, the bar material will remain on the machine centre line, minimising run-out and enabling tighter concentricity to be maintained during the cutting process.

With the AGB system, a protective shield disc is provided to minimise contamination from fine particles of swarf and, with its locking nose cap, quick and easy removal from the front of the machine spindle is possible using a wrench and pin spanner.

The unit can also be assembled away from the operating area.

Find out more about this article. Request a brochure, download technical specifications and request samples here.

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