Thread: Extreme Lapping

A while ago I was reading a small page of the Science of Sharp website where he put a barber hone under an electron microscope to show that the abrasive particles were not particularly fine, something like 600 grit. The fine cutting action of the hones was primarily achieved by some type of conditioning/lapping of the surface that knocked the peaks off of the abrasive in the stones.

About the same time I came across this video of a guy making some toolroom stones for deburring various machined parts.

https://www.youtube.com/watch?v=DVLXsq7pi9Y

By surface grinding the stones he basically reduced their ability to cut so much that the abrasive would not initiate any type of scratching at all.

I have always wondered whether anyone has experimented with lapping something like a fine india stone to some very fine level, enough that the stone acts way way finer than its nominal grit rating, maybe even good enough to finish a razor on?

I have a 6 inch india stone going unused since I have a larger one which I use now and I have thought about lapping it using some SiC and lapidary diamond but before I try I was wondering if anyone had ventured into these waters before and whether I'd be wasting my time.

Many thanks.

I know that people will burnish a Arky to make it finer but i'm not sure about a india stone. Seems that no matter what kind of stone it is that it would have to be hard enough not to wear away and expose new abrasive particals. Only way to find out would to be to try it i guess. let us know what you come up with.

As Robin says at about 7.05 in the video.
“The nature of this is completely contrarian to normal stoning like mould polishing where you want the abrasive to be aggressive. This is a completely different stone.”

The goal of these stones is to polish a flat surface. Dead flat for honing is not that important, you want stones that will cut a progressively finer smoother edge and very few razors are flat. You are polishing a surface that is 1-2mm wide. The goal of polishing a bevel is to make a straight edge with smaller serrations, not a shiny bevel. But the only way to hone the edge is to polish the bevel. A shiny flat bevel is the by-product of a straight finely hone razor edge, not the goal.

You can polish a bevel with any good metal polish that is mirror finished, but the grit in metal polish (usually Aluminum Oxide) is large and aggressive and will leave a serrated edge, unsuitable for shaving, great for knife, and tool edges though.

With deburring stones, (320 grit India stones) you are polishing much larger surfaces, with large grit that has been flattened.

Robin does not show you what the surface looks like under magnification, because it is not important to his objective, he is after flat, not polish. To the naked eye a good 8k bevel looks like a mirror finish, under 60-100 x magnification you see all the imperfections and what they do to the edge of the work piece, not all 8k’s are equal.

As said, all he is doing is burnishing a stone face. The same thing happens with old sandpaper, the space between the grit fills with swarf and the grit flattens out. Allowing or forcing the paper and grit to make a smoother surface. The grit is still the same grit in width, just not in height, and will cut stria the width of the grit. In this case you are cutting 320 grit stria.

Robin also states “There are no other methods to do it that work. You can’t lap them. You need a good surface grinder and diamond wheel.” (You need to cut the tops of the grit uniformly).

You will also need 2 identical stones to maintain flatness, after every few laps you must rub the two stone together to flatten the swarf between the grit in the stone.

Probably a more practical video of Robin’s is his surfacing lapping plates. But here again, dead flat is not critical for honing razors. Robin is a pretty smart guy with some great videos on his channel.

Technique trumps stone grit and flatness every time. India stones are great for repair work and great knife and tool stones.

Grit particles are round and to some extent spikey little things. You may be able to flatten those with a finer-gritted stone and that way change their sharpening properties. My guess is that it will at best create a very slow stone and you'd be better off buying a higher-grit size stone.

Originally Posted by Euclid440

As Robin says at about 7.05 in the video.
“The nature of this is completely contrarian to normal stoning like mould polishing where you want the abrasive to be aggressive. This is a completely different stone.”

The goal of these stones is to polish a flat surface. Dead flat for honing is not that important, you want stones that will cut a progressively finer smoother edge and very few razors are flat. You are polishing a surface that is 1-2mm wide. The goal of polishing a bevel is to make a straight edge with smaller serrations, not a shiny bevel. But the only way to hone the edge is to polish the bevel. A shiny flat bevel is the by-product of a straight finely hone razor edge, not the goal.

You can polish a bevel with any good metal polish that is mirror finished, but the grit in metal polish (usually Aluminum Oxide) is large and aggressive and will leave a serrated edge, unsuitable for shaving, great for knife, and tool edges though.

With deburring stones, (320 grit India stones) you are polishing much larger surfaces, with large grit that has been flattened.

Robin does not show you what the surface looks like under magnification, because it is not important to his objective, he is after flat, not polish. To the naked eye a good 8k bevel looks like a mirror finish, under 60-100 x magnification you see all the imperfections and what they do to the edge of the work piece, not all 8k’s are equal.

As said, all he is doing is burnishing a stone face. The same thing happens with old sandpaper, the space between the grit fills with swarf and the grit flattens out. Allowing or forcing the paper and grit to make a smoother surface. The grit is still the same grit in width, just not in height, and will cut stria the width of the grit. In this case you are cutting 320 grit stria.

Robin also states “There are no other methods to do it that work. You can’t lap them. You need a good surface grinder and diamond wheel.” (You need to cut the tops of the grit uniformly).

You will also need 2 identical stones to maintain flatness, after ever few laps you must rub the two stone together to flatten the swarf between the grit in the stone.

Probably a more practical video of Robin’s is his surfacing lapping plates. But here again, dead flat is not critical for honing razors. Robin is a pretty smart guy with some great videos on his channel.

Technique trumps stone grit and flatness every time. India stones are great for repair work and great knife and tool stones.

I understand the purpose of the stones in the video, I guess my point was that it seems to be a similar mentality to the way barber hones were produced, a deadening of a relatively coarse abrasive. The article I referenced is here:

https://scienceofsharp.com/2015/08/28/the-barber-hone/

Now the nominal 600 grit in this particular barber hone is not what one would finish a razor on, but by lapping the abrasive it obviously creates a much finer seeming stone. I have an old barber hone and you can actually see the abrasive particles with nothing more than a 15x loupe, however when I have put a razor to the hone it leaves a very fine finish, not true finisher fine but much finer than you would expect from a stone where you can see individual particles of abrasive.

Something else interesting on the site was the cutting action of a 325 DMT plate leaving a cleaner apex than the finer plates:

https://scienceofsharp.com/2015/03/0...e-progression/

My own interest in lapping that india stone was to see if it was possible to create a sort of barber hone type stone by sufficiently knocking down the abrasive, not really to create a flat surface or anything.

My own interest in lapping that India stone was to see if it was possible to create a sort of barber hone type stone by sufficiently knocking down the abrasive, not really to create a flat surface or anything.

I am sure that the diamond edges could have been improved with a bit better technique. Some of the stria looks Pollock-ish. Diamonds are much maligned and misused. I frequently use diamonds for repairs and honing tools and knives.

The edges could have easily been improved with a simple edge jointing and lite re honing.

My point is that those India stone were created/modified for flattening, not edge refinement. It is very much like burnishing a hard Ark, which has a hard binder and comparatively large grit and can produce edges that rival .50um synthetic stones, and Jnats which are a mystery unto themselves.

My, hone experimenting day are pretty much done. I mostly hone on a King 1k, refine on a vintage, wood- based King-S-3, a rate 6k stone that can take a 1k edge to near 12k Super-Stone edge, and then to an Ark or Jnat for finishing. Quick and simple.

Some folks say one could lap an India if you use 3 stones technique, but it is a lot of work.

Rock on, post your results if you do it.