Spotface

Combination drills known as Subland drills combine a number of operations in a single tool e.g. drill and ream, drill two diameters, drill and chamfer, drill and spotface, drill and counterbore. Fig. 8.10. Each cutting edge has a separate land and flute. Fig. 8.11, which enables cutting to take place and resharpening to be easily carried out. 

A spotface cutter. Fig. 8.15, is used to provide a flat and square seating for a screw, bolt or nut on the surface of the workpiece, usually on the surface of a rough casting which would not otherwise provide a sufficiently accurate seating. The spotface is similar to a counterbore cutter, but has teeth on the end only. It will cut to only a very limited depth and caimot be used to counterbore. Counterbore cutters, on the other hand, can be used to spotface. 

In some awkward places, back or underside spotfacing is required. Fig. 8.16. The pilot is fed through the hole and the cutter is fixed to the pilot, usually by some quick-locking mechanism or a simple grub screw. When the operation is finished, the cutter is removed and the pilot withdrawn. 

Counterbore cutters, on the other hand, can be used to spotface. 

Jordan, D.L, Franks, L.L. and Kallend, J.S., Measurement of underfihn corrosion propagation by use of spotface paint damage, in Proc. Corrosion 95, NACE, Houston, 1995, Paper 384. 

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