Slurry Edge Dulling, Convexing and Micro Chipping

Slurry Edge Dulling, Convexing and Micro Chipping

There has always been an on-going discussion about slurry and edge dulling vs sharpening. And the art of creating, and use of slurry for cutting vs polishing.

The “Art” part is the ability, to read slurry and creation for a specific use, cutting and or polishing, (they can be very different), thick/thin, Diamond vs Tomo slurry or other slurries.

The old school, of creating a thick slurry and thinning to clear water has always produce mixed results, hence the mystery and Art. But why?

Recently, I viewed the Micro Graphs of swarf posted, on the Science of Sharp website, in the (Swarf post).

It was interesting to see the shape and size of swarf at magnification, but makes a lot of sense. Based on what we see from grading body filler, probably the most graphic example of a similar process in a larger scale the metal swarf is shaped in curly cues, almost like micro springs, where metal is scraped from the bevel to form a groove/stria by the grit of the stone.

This post, also is in keeping with Alex Gilmore’s theory and post (on honing on slurry and swarf and search for the cause of edge blunting), on his site, and his findings on, making a bur intentionally, then removing it to, re-set and make a solid v shaped edge, (the japanblade.com/blog), (Why Develop a False Edge on Purpose?)

Alex theorizes about a wave of thick slurry, forming at and under the edge, in an edge leading stroke. The aggressive cutting power of thick slurry can convex the very edge by aggressively honing at the edge. The results can be the edge worn and micro convexed.

But added to Alex’s observation, is swarf. In effect the edge is hydroplaning on slurry and the rounded (springs) of swarf. Especially if light pressure is used in the final laps, while using the same slurry, the edge can become both convexed and damaged, (Micro-chipped).

While the conventional, theory for the slurring naturals, has been to break down the slurry, with repetitive strokes, there is a fine line where the slurry is getting finer, swarf is added to the slurry, and the edge burr/fin lengthens, further impacting the edge and convexing the very edge and possibly weakening the edge.

When, then a clear water honing is performed, with light finishing strokes, the edge is not in contact with the stone, and may be damaged by the swarf and can fracture and micro-chip and not touch the stone.

A lot is going on at the edge, of a slurry honed, edge leading stroke, none of which we can observe, in real time.

While slurry thinning, and working with repetitive laps, will break down some slurry, there is a point of minimal return, where breakdown is maxed, addition of swarf is detrimental to the edge and additionally, the fin is lengthened, especially with large number of laps and not re-newing the slurry.

Alex recommends fewer laps and making new slurry to keep the cutting power of the slurry maximized, (and free of contaminants, swarf). Of course, knowing your slurry, how aggressive it is and how quickly it breaks down and feeling, when cutting is minimized, is literally in the hands of the honer and formulaic honing goes out the window, as it should.

What are your thoughts on these two theories and the combined effect on the edge, and what is your experience?


Sorry forgot to link the two post in question.

Am I to take your hint that finishing with 100+ x-strokes on water alone (on hard coticule or slate) may not be as beneficial as, say, 2 x (10-15 strokes on fresh thin slurry)? Could this also explain why using oil, or Smith's, or even soap instead of plain water tends to result in 'better' edges. More than just reducing the surface tension, do these lubricants also lift the swarf and other contaminates off the stone so they do less work.

Quote:

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Originally Posted by Euclid440

Alex theorizes about a wave of thick slurry, forming at and under the edge, in an edge leading stroke. The aggressive cutting power of thick slurry can convex the very edge by aggressively honing at the edge. The results can be the edge worn and micro convexed.

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Maybe so... But I have seen the opposite with slow cutting stones where the slurry floats the edge off the stone & & hones the shoulder more.
It's a bit hard to generalise.

I asked Tim Zowada, years ago, if he used slurry on his Escher. He replied that he saw no point in "dragging his razor through the mud." At that time I also asked Lynn Abrams, and he didn't use it with his Escher either. I've gone back and forth.

For awhile I would generate a thin slurry on an Escher because the instructions on the label recommend that. I'd thin the already thin slurry as I went. I can't say for sure that the results are better than plain water, but I basically still do that when I use an Escher.

For me honing is still somewhat mysterious, I learned the moves. I do them and sometimes I get the bear, and sometimes the bear gets me. :)

“Am I to take your hint that finishing with 100+ x-strokes on water alone (on hard coticule or slate) may not be as beneficial as, say, 2 x (10-15 strokes on fresh thin slurry)? Could this also explain why using oil, or Smith's, or even soap instead of plain water tends to result in 'better' edges. More than just reducing the surface tension, do these lubricants also lift the swarf and other contaminates off the stone so they do less work.”

As I see it, maybe. We can’t see what is happening at the edge, we can only see the results, if we look at each stage. But if you are honing on a heavy slurry, with swarf in it and your edge is not improving, (getting straighter or chipping), stop and wash off the slurry and swarf and make new slurry and see if it improves.

I know for a fact that with stones, that load up easily, like the Super Stones, that a stone with swarf will not cut as fast or as clean (leave scratches on the bevels) as a refreshed stone face. I suspect it is/was the swarf.

On those stones, most synthetics, especially the higher grits, I clean and refresh the face and do a set of final laps on a clean water or very light slurry.

On stones that I use oil, it is usually a drop or two Smiths or Ballistol on a wet stone and I finish with the same procedure, on a clean stone. I suspect that oil may suspend the swarf better, I know that soap works better.

Recently another of Alex’s videos, talked briefly about using a very little bit of pure soap in his water with good results. I have been using Dr Bonner’s Castile Soap concentrate, just because it was easy to find, Walmart, 1 drop in a 2-oz. squeeze bottle of water. Dr. Bonner’s is made from a variety of oils.

When you add a drop of this diluted soap, to new slurry on a stone, you can see the slurry break up immediately, in a bloom and spread across the stone. The soap or the lack of clumping seems to aid in the clean cutting, when needed, I add additional plain water, a drop at a time from a squirt bottle.

Do not use soap on synthetic stones without testing, most synthetic stones, specifically say, Not to use Soap. I placed a drop of Dawn dish soap on an 8k Norton, years ago. It ate a ¼ inch divot in the stone and it is still there years later and after years of use and lapping, though it does not appear to affect honing, though I rarely use the stone these days.

For me, the goal is to get the swarf and some of the slurry to float over the edge and not under. While extensive honing can convex the edge, swarf can also keep the edge off the stone and damage the edge.

Now I only hone on naturals to finish, 8 or 12k edge, so I am not looking for aggressive cutting power.

The other interesting theory is the length of the burr/fin caused by too many finish laps.

The question then becomes, how much is too much?

Quote:

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Originally Posted by onimaru55

Maybe so... But I have seen the opposite with slow cutting stones where the slurry floats the edge off the stone & & hones the shoulder more.
It's a bit hard to generalise.

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What you are seeing may be what Alex is talking about, and the very edge may be microscopically convexed, and when put on a hard flat stone the edge is not making contact, and the back of the bevel is polished.

Or could be hydro-planning also. Hard to say, either way, the edge is not in contact with the stone.

Quote:

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Originally Posted by Euclid440

What you are seeing may be what Alex is talking about, and the very edge may be microscopically convexed, and when put on a hard flat stone the edge is not making contact, and the back of the bevel is polished.

Or could be hydro-planning also. Hard to say, either way, the edge is not in contact with the stone.

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Was done on a 'test' kana blade. The edge was untouched so I'd suspect hydro-planing.

Sounds similar to some of the observations that John Juranitch detailed many years ago about using liquids on a stone. He had microscope photos showing the damage through several phases of the sharpening process if I recall correctly.

I have been advised that Solvol Autosol is much too aggressive to use to create a slurry, but are there other alternatives to a slurry stone that people have found positive? Has anyone tried a finishing compound (such as Farecla G10)?

Yes, I have tried adding abrasives, the problem with using abrasives like you described, (abrasive/polish) is, 1. We don’t know what the abrasives is/are, and 2. We do not know the grit size. Polish manufactures are very proprietary about the contents of polishes.

I have tried honing on Nano grit abrasives like Diamond and CBN down to .10um and while it can add aggression, it is better to finish separately on the hone, then strop on known grit size abrasives. So that incase of issues, it is easier to de-construct and isolate the cause.

Some polishes work well for polishing, removing bevel stria, but contain Aluminum Oxide or other abrasives, that will leave a harsh, chippy edge. Autosol, Maas and most metal polishes as well as paint cutting compounds are like that. I have tried most but not Farecla G10.

In this post, I was talking about, Nano convexing the edge of a bevel, on thick, natural slurry, so that when diluting to clear water, on a hard-natural finish stone, the edge is no-longer making contact, but the bevel is.

Added to that, excessive swarf could be floating the whole bevel and edge off the stone or at least not making, full contact.

I had never seen SEM micrographs of swarf, and was surprised at the size and random shape or the swarf. So that thick slurry and swarf could easily affect, bevel-to-hone contact and more importantly, edge-to-hone contact with swarf larger than the grit size of the slurry.

Thank you, and I think I follow, that with too dense a slurry while the trailing edge of the bevel is held in contact with the stone by manual pressure, the leading edge itself is lifted out of contact and this is exacerbated as the water content evaporates off the surface of the stone, resulting in a bowing of the bevel?

Almost, it is not uncommon for folks to have issues of harsh edges, when honing on clear water, to blame the stone for chipping the edge, a common complaint on Jnats and Coticules.

When honing on natural stones, using slurry is common. One begins with a thick-ish slurry and thins the slurry to clear water, no slurry. But often when honing on clear water, edge chipping occurs and the honer blames the stone.

Recently in another forum a honer made the same complaint and sold the pricy new stone. The new owner, said he was able to get very nice shaveable edges from the stone without issue. It was not the stone, but technique that was the problem. But why did that happen?

It may be the edge is convexed and then breaks off, after flexing on the hard-flat stone, so the issue is not the stone but technique, possibly slurry convexing and possibly swarf, beating the edge.

Alex, theorizes that a thick slurry can abrade the edge, more than the bevel (edge leading) and cause micro convexing at the edge. So that when, the same bevel and edge is/are honed, on plain water and a hard stone, the edge may not contact the stone, preventing the stone from cutting the fin/edge, off cleanly to form a straight edge.

If that is so, excessive honing on slurry, on an aggressive stone/slurry will have a lot of swarf, in front of and under the bevel. So, you can have, a convexed edge and excessive swarf, further keeping the edge off the stone.

Alex’s theory is the possibility of convexing of the edge, I am asking if you add the swarf shown in the micrographs, would that not exacerbate, the issue of convexing, and edge dulling, or at least keep the edge off the stone, preventing it from honing the edge, and then the edge breaks off?

On natural stones that use slurry, the practice of honing on slurry excessively, to break down slurry is common, this practice can cause both issues, convexing and dulling from swarf.

A simple solution is to make new slurry to finish and not keep working the slurry loaded swarf and use a progression of finer/thinner slurry.

Got it, thank you.