Marginally lubricated

Machining8then the pilot guide and rear supportshould be longer than the distancebetween the two bushes.• For large bushes it may be necessary toprovide axial relief along the length ofthe pilot guide and rear support, in orderto reduce the broaching forces.• Unless a guided broach is used, the toolwill follow the initial bore alignment of thebush, broaching cannot improve concentricityand parallelism unless externalguides are used.In general owing to the variation in wallthickness of large diameter bushes,broaching is not suitable for finishing boresof more than 60 mm diameter unless externalguides are used.8.5 VibrobroachingThis technique may also be used. A singlecutter is propelled with progressive reciprocatingmotion with a vibration frequency oftypically 50 Hz. The cutter should have aprimary rake of 1.5° for 0.5 mm.A cut of 0.25 mm on diameter may bemade at an average cutting speed of 0.15m/s to give a surface finish of better than0.8 µm R a , which is acceptable.8.6 Modification of componentsThe modification of DX bearing componentsrequires no special procedures. Ingeneral it is more satisfactory to performmachining or drilling operations from thepolymer lining side in order to avoid burrs.When cutting is done from thesteel side, the minimum cutting pressureshould be used and care taken to ensurethat any steel or bronze particles protrudinginto the remaining bearing material,and all burrs, are removed.8.7 Drilling Oil HolesBushes should be adequately supportedduring the drilling operation to ensure thatno distortion is caused by the drilling pressure.8.8 Cutting Strip MaterialDX strip material may be cut to size by anyone of the following methods. Care mustbe taken to protect the bearing surfacefrom damage and to ensure that no deformationof the strip occurs.• Using side and face cutter, or slittingsaw, with the strip held flat and securelyon a horizontal milling machine.• Cropping• Guillotine (For widths less than 90 mmonly)• Water-jet cutting, Laser cutting31