Just to be sure that we are talking about the same thing...I was talking about the DMT Diafolds and to a lesser extent the bench hones, all of which are a thin layer of steel mounted to a piece of plastic. DMT also do all-steel plates.
I admit that my DMT Diafolds, used for knives, seem to give pretty even cutting, in contrast to the standard ceramic hones by either Spyderco or Fallkniven, which usually show undulations and high spots. However, pieces of moulded plastic are not known for dimensional regularity or stability. If they were flat, guaranteed, then the manufacturer that achieved that would be shouting it from the roof tops, attracting customers away from all the alternatives and competition.
When I am interested in flatness it tends to be either because I want to use all the surface of the sharpener, not just the high spots, or because I want to work through grits on a wide area and want each successive grit to reach the full surface. I am not all that bothered about plane soles, compared to the backs of chisels and plane irons. I haven't tried using a series of DMT Diafold hones for this job, but even if they were dead flat, the smaller size would argue against using them except in a pinch.
I've got a kind of selection.
The Diafold which is so small that its flatness just doesn't make a difference.
Handy for knives and router bits though.
The 600 mesh 50x150mm or so DMT bit of steel with holes and stuck onto a thick ish glass re-enforced plastic isn't the biggest either but manages to flat off chisel backs and small plane blades.
For my Stanley 5 1/2 Stanley 6 need something a bit bigger.
Got a cheapo Faithful 400/1000 hone for that. Again surprisingly flat.
Admittedly I've not feelergauged it but have sighted it with a straightedge.
Its good enough for my 5 1/2 Jack and 6 Foreplane blades.
The blade on my fivers worth of wooden jointer (that had the parallel Norris blade which Ive seen on sale for ￡95, Yay) looks like David Blunkett flatted it off on his front step.
The last 2mm from the edge could really do with an attack of a Tormek.
I have a mate with one I can borrow but even as it is the damn thing just works and its as good if not better than my Stanley 6 with uber posh Veritas blade.
That does not mean I'm saying that all wooden planes are brilliant and all metals arent.
Nope, it just means that the last three wooden planes I've bought (Lignum Vitae soled german pattern toothing plane, 550mm old English pattern Beech wooden jointer and Lignum Vitae soled German pattern but made in Holland ABC smoother have worked out well for me.
Cheap enough to buy several and leave them setup with the blade out and use each for a slightly different task.
On site is a different matter and my 5 1/2, Veritas blockplane and De-Walt cordless planer are more versatile and I don't need a trailer full of handplanes to make a days wage.
Personally I really rate diamond hones, especially on site where stones are a bit fragile and there seems to me to be a level of waterstone thats just expensive and not significantly better than polishing compound on a bit of wood.
I've not tried the green compound on leather yet, not felt the need but I do have a decent length 100mm wide strip of leather to try it on at some point.
I'm not trying to tell anyone they're wrong. I'm just suggesting they give things a bash and maybe measure stuff. My opinions have had a bit of a revision over the last couple of years (thats code for I realised I was plain wrong) and I realised I needed to actually test things more and not just believe tool catalogues.
Its also quite possible that I'm just chuntering on about my own personal "journey" (Buzzword Bingo yay) but my main point is for people to have a go, test stuff as scientifically as they can, measure things.
