flattening stones

D

drail

Joined
Feb 23, 2008
Messages
542
Over the years I have tried various methods of flattening my stones. They are all either Norton India or soft Arkansas stones. I was able to get them reasonably flat using Zircon sandpaper on a flat plate but it took a lot of time and work. I kept reading about guys using silicon carbide abrasive on a flat concrete block or ceramic tile or a thick piece of float glass, and how it works much faster and easier so yesterday I bought a nice flat 14 X 18" paving block ( 92 cents at Home Depot) and some 60 grit silicon powder and went at it. I took an old silicon carbide rub brick I had laying around and knocked the high spots off of the concrete block before I started but it was surprisingly pretty smooth and flat. I am totally blown away at how quick and easy it went. Both the India and Arkansas stones are like brand new. If you need to flatten traditional hard stones try it. Just keep flushing off the block with water and adding a little more powder as you go because it will break down pretty quickly. I was surprised that the soft Arkansas stones seemed to be getting cut faster than the Norton fine India. That thing is hard.
 
Yup. It works so fast because instead of abrading the stone away it's creating massive point-pressure that attacks the bond of the grains. Much faster than trying to abrade an abrasive.
 
You can find it pretty easily on eBay or elsewhere on the web if you look for the coarse grit for rock tumblers. It's typically a coarse black silicon carbide.
 
Trick is getting some less friable silicon carbide, it will last a lot longer before you need to add more. The black variety is much tougher.
 
I don't know of anywhere that sells green SiC loose grit, so the black should be pretty much what's sold everywhere. Green is a small percentage harder than the black but is more friable, though not a huge amount so. One relative scale I recall rated the relative toughness of black at 1.75 units and green at 1.6 IIRC. Regardless, even black SiC loose grit breaks down fairly quickly when lapping stones, so if you want a "true" surface at the grit level you're using, keep the grit fresh.
 
Just a pain to do with lots of Sharpening. I prefer it but I'll just use a SiC stone flattener or Atoma 140 more often for convenience.
 
For certain hones, I flatten with a diamond plate then just kiss the surface with SiC loose grit and a small flat piece of tungsten carbide. Best of both worlds - quick and perfect surface texture.
 
@FourtyTwoBlades, do you think there is much truth to the thinking that grit becomes ground into the stone and takes some sharpening to
wear this off? DM
 
David Martin said:
@FourtyTwoBlades, do you think there is much truth to the thinking that grit becomes ground into the stone and takes some sharpening to
wear this off? DM
Click to expand...

Grit will only risk being embedded in very soft stones like Japanese water stones, and those will lap flat quickly on a cheapo diamond plate or SiC flattening stone.
 
I have never had that problem. The stone would have to be extremely soft for that to occur, or the abrasive would have to be set in with an impact. By the nature of the loose grit lapping process it pretty much eliminates this as an issue, since the abrasive basically cuts into the stone's binder and releases stuck abrasive particles. I have always just done a good rinse and scrub with a nylon brush after lapping and never had any issues. Considering that the abrasive is black, I have never seen any embedded in a light colored (white, yellow, etc.) hone either. Of note is the fact that Shapton for many years used to sell cast iron lapping plates and loose SiC grit for resurfacing their hones. Then they came out with their diamond plates. Not sure if they still sell the cast iron plates and loose grit.
 
I think the reason why that thought floats around is because Shapton and Naniwa have cautioned against using sandpaper to flatten their stones as they claim it can cause grit and/or adhesive to lodge in the stone. However, I have yet to see any concrete evidence that this actually occurs, and rather doubt it would.
 
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