A Look at Drill Sharpening informed by 3D CAD

摘要

I will pass on some information about drill point geometry that could be of some help when drill sharpening, as we are more efficient when we know what we do. We want to grind 2 symmetrical lips at the right angles with no rubbing of the drill heel at the bottom of the hole to be drilled, see drawing 1 for drill point definition. To test the clearance (for not rubbing) I used 3 D CAD for the following process (see drawing 2): I made a model of the drilled hole, but in negative (as if some molten material had been cast inside), yellow colored. It can be noted that the bottom of the hole is not a conical surface, but a hyperboloid one, because of the web thickness which causes the (straight lines) cutting lips not to cut on the drill axis (the center part made by the chisel edge will be dealt with later). I made a model of the corresponding drill point, blue colored, with straight flutes (far easier to make than the helical ones, and of the same use for studying the clearance); the 2 pieces are then 'assembled' in a working situation.