Some time ago I decided to grab the Shapton 120 for heavy reshaping work (reworking primary bevel, damaged blades, etc). It was amazing for this the first 3 or 4 times I used it, however since them it seems like I’ve “smoothed” it. Yesterday I was trying to resurrect it, I tried levelling it, rubbing with a 300 diamond grit plate, I then got desperate and tried hitting it with 60 grit sandpaper. After all this, I still found that it was polishing my plane blade; it’s basically just hard and smooth at this point. I tried to keep going until I’d produced a bit of slurry, this took a lot of time and still didn’t work close to as aggressively as my 300 diamond plate.
I have other Shaptons and love them, so I’m wondering if I’m missing something with how to properly maintain this coarse version? Do I need to buy a real lapping plate or something? Appreciate any insights.
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I use a coarse diamond plate larger than the shaptons to flatten mine. I draw a bunch of pencil lines on the face and go to town until the lines are gone.
Thanks! Yes that's exactly how I do my higher grit stones too, unfortunately with the 120 it doesn't seem to have the same impact. I'm guessing I probably need a proper lapping plate, but I'd like to make sure that will fix it before I invest, those things aren't cheap (and the 120 Shapton is at the cheaper end, and probably not worth it alone).
Curious if you have called Shapton to ask them. This does sound really odd but I've never used that coarse of Shapton stone. I think my most coarse Shapton is 1000 grit. I can't imagine you need a diamond lapping plate to fix this. Sounds like something wrong with the stone.
I don't have a 120 myself (yet). That said, in my online research I've found that the consensus of opinion is to use 30 or 60 grit silicon carbide on glass to re-rough and flatten the surface. People also report luck with 60 grit 3M cubitron sandpaper and 60 grit foam-backed diamond hand sanding pads.