The influence of not flattening waterstones on sharpening angles

The argument made popular by Murray Carter is that flattening waterstones is wasteful as it throws grit away which could be used to sharpening. This is true in an absolute sense but it ignores the fact that non-flat stones will increase the edge angle in a random manner based on the depth of the hollows in the stone.

This has two consequences, the first is that the direct angle increase which is going to be fairly random due to the inconsistent nature of the non-flattened stone is going to reduce cutting ability and edge retention (in general). It is also going to increase honing times because when the edge is raised due to hitting a hollow it will not be effected at all by the flat section of the stones until they grind away that heavier angle that the hollow applied.

The second consequence is that if you then move to a harder stone which is closer to flat then you will be sharpening at a different angle to the stone even if you hold the same angle because the harder and flatter stone will not have those hollows. This is why people often struggle to refine an edge when they switch to a finer stone or in fact make the edge go dull because the stone isn't grinding against the edge only the mud / slurry is grating against it and dulling it.

Note as well that even with regular flattening, a waterstone which is used for aggressive shaping such as this one (a Bester 700X) has a lifespan which is on the order of a half a million passes. Thus the argument that it is wasteful to flatten is largely academic because the actual cost or dollar value being lost is extremely low.