In another thread last year I made a postulation that waterstones require a stupid amount of maintenance because they go out of flat pretty quickly. I think I can now quantify this theory a little more clearly than perhaps I did back then.
Next door neighbour was given some rusty old Marples (blue plastic handle jobbies that could be had in the 80s, at least), so I offered to rehab them for him. Some of the "bevels" were convex, and a few had chips that were pretty rugged, and so at one point I broke out the 120 Shapton in preference to the 220 (?) Atoma diamond plate. I do not have a bench grinder, which was what was really required for this major work.
Based upon my theory from last year, I figured that I may be making a rod for my back by using this waterstone (freshly flattened). Indeed, this proved to be true, because when I came back to the Diamond plates (to ensure flatness of the bevel before moving on to diamond paste on cast iron blocks up to 14k) the shape of the bevel from the waterstone did not match the diamond plate - i.e. it was not flat off a flattened stone (maybe did 300 strokes on the Shapton from freshly flat).
I completed the job this arvo, and then flattened the waterstone again before retiring it back to the box (from which it will be lucky to get wet again) - it took a fair bit of work just to correctthe dishing from those 300 or so strokes - about another 300 strokes on the 10" Diamond plate.
So, a freshly flattened stone was no longer flat after about 300 strokes (up and back is one stroke), which is not much - perhaps 3 or 4 minutes work. At a microscopic level, the flatness of the stone is affected from the very first stroke, and it's all downhill from there. That means that the stone itself would need flattening, say, every 50 strokes, or one minute's work.
I think what exacerbates this is that the stone will take on the shape of the existing bevel, which in this case was all over the place. These chisels had clearly been sharpened freehand by somebody without the talent/practice to do so (I use a Veritas sharpening jig because I don't either). This "shape taking" by the waterstone means that there will be freshly ground steel across a bevel much earlier than when it is actually flat (and which it never will be), thereby giving a false impression that the job is done to completion. Move on to the next grit (of whatever medium) and find out that this is not the case at all.
CAVEAT: I am not saying that waterstones won't give a good edge - they do - just that for major work they can't be trusted to deliver flatness without constant flattening. Mind you, it would a pretty insanely sharp edge to convince me that they are better than diamond paste (especially for all the associated fuss with waterstones). As Mr Brush points out, that insanely sharp edge is coming back to sanity after not much woodworking anyway.
Next door neighbour was given some rusty old Marples (blue plastic handle jobbies that could be had in the 80s, at least), so I offered to rehab them for him. Some of the "bevels" were convex, and a few had chips that were pretty rugged, and so at one point I broke out the 120 Shapton in preference to the 220 (?) Atoma diamond plate. I do not have a bench grinder, which was what was really required for this major work.
Based upon my theory from last year, I figured that I may be making a rod for my back by using this waterstone (freshly flattened). Indeed, this proved to be true, because when I came back to the Diamond plates (to ensure flatness of the bevel before moving on to diamond paste on cast iron blocks up to 14k) the shape of the bevel from the waterstone did not match the diamond plate - i.e. it was not flat off a flattened stone (maybe did 300 strokes on the Shapton from freshly flat).
I completed the job this arvo, and then flattened the waterstone again before retiring it back to the box (from which it will be lucky to get wet again) - it took a fair bit of work just to correctthe dishing from those 300 or so strokes - about another 300 strokes on the 10" Diamond plate.
So, a freshly flattened stone was no longer flat after about 300 strokes (up and back is one stroke), which is not much - perhaps 3 or 4 minutes work. At a microscopic level, the flatness of the stone is affected from the very first stroke, and it's all downhill from there. That means that the stone itself would need flattening, say, every 50 strokes, or one minute's work.
I think what exacerbates this is that the stone will take on the shape of the existing bevel, which in this case was all over the place. These chisels had clearly been sharpened freehand by somebody without the talent/practice to do so (I use a Veritas sharpening jig because I don't either). This "shape taking" by the waterstone means that there will be freshly ground steel across a bevel much earlier than when it is actually flat (and which it never will be), thereby giving a false impression that the job is done to completion. Move on to the next grit (of whatever medium) and find out that this is not the case at all.
CAVEAT: I am not saying that waterstones won't give a good edge - they do - just that for major work they can't be trusted to deliver flatness without constant flattening. Mind you, it would a pretty insanely sharp edge to convince me that they are better than diamond paste (especially for all the associated fuss with waterstones). As Mr Brush points out, that insanely sharp edge is coming back to sanity after not much woodworking anyway.
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