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Dossier(Sketch 1)The sectional drawing of a fixed guide bush (left) shows thecarbide guide surface marked in blue. The enlarged detail(top) shows the lubrication film (yellow), which hydrodynamicallyseparates the guide surface and the bar material.Because of a special surface structure with so-called“micro recesses”, the cutting oil has maximum adhesion and,thanks to special MOTOREX additives, forms a high-performancelubricating film.precipitous rise in temperature severely reduces theviscosity of the lubricant and demands maximumperformance from the machining fluid. For thisreason, MOTOREX uses a combination of temperature-stableextreme-pressure additives in its ORTHOcutting oils.In the case of the “turning” guide bushes, direct frictionbetween the surfaces can be prevented. Theturning movement takes place in the spindle and itsball bearing. However, the spindle bearings mustonly have minimum play. In the case of the “turning”guide bushes, they heat up linearly, which canbe described as unproblematic.The latest carbide and ceramic guide bushesFor carbide guide bushes various manufacturers,including Walter Dünner SA of Moutier, now usehard metals containing cobalt. In detailed series oftests, it has been discovered that cobalt has a desirable,friction-reducing effect. At Dünner the guidesurface is also given a special grinding, which leavesbehind the required “micro recesses”. This enablesthe cutting oil to adhere better and to convince, byproviding a highly stable lubricating film (sketch 1).In all events, the guide surface should be lapped,which unfortunately is not always the case todaywith all manufacturers. It is precisely in the case ofThe well thought-out MAGIC guide bush system from Walter Dünner SA enables the bush to be opened and closed automatically. If a bar is worked, apartfrom a small residue, then this simplifies the ejection of the remaining bar from the bush. Once the new bar has been inserted, the MAGIC guide bush automaticallyadjusts to the preset value!36 DECO MAGAZINE 03 / 06