Any suggestions on how to flatten a hard Arkansas stone?

First, a comment on the aggressiveness of the cut. A hard black arkansas is the last in the series of arkansas stones that you use to
sharpen a blade. You would start with a washita, then a white and finally a hard black. The hard black is for putting a final mirror- finish razor-sharp edge on a blade. It removes very little material because of its fine grain. Your belief that it is not cutting well may be wrong if you are trying to use it for the initial sharpening.
There are two primary home-brew methods for flattening a stone. The first is rub it on a diamond hone of the same size or bigger. This is the more expensive option. The other method is to use silicon carbide grit or silicon carbide paper on a piece of float glass or surface plate. The stone is rubbed on the surface until it is flat. I have heard that using the grit is faster, but it will eventually wear a hollow in the glass plate. Using paper protects the glass. The silicon carbide appoach is slower than the diamond and depending on how much material must be removed may take a significant amount of paper or grit.
I would not use a wheel grinder to flatten the stone as I believe that it would be too hard to control and could possibly ruin the stone in a few seconds. You also need to consider the type of blades you are sharpening as to how flat the stone should be. If you are sharpening plane irons or chisels, the stone should be dead flat. If you are just sharpening your pocket knife the hollow is probably inconsequential.
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The latter is the way I flatten a synthetic stone, but have you tried it with Arkansas stones? I didn't pipe up on this part of the question because I've never tried to flatten a natural stone -- because I've never had to. But it's an interesting question.
-- Ed Huntress
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In lapidary circles, there is a machine called a vibrating flat lap. It consists of a big metal pan and plate mounted on springs with a motor and an eccentric weight .
It is used to polish cut geodes and stone slabs. You charge it with coarse abrasive, put your stones on it (weighted if need be) turn it on and come back in a few days to charge it with finer abrasive.
It would probably flatten a hard Arkansas stone pretty readily.
However, I cannot imagine a hard Arkansas stone getting that wallowed out, Washita maybe but not a black.
As a side note, I was taught to never use oil on one of these, it just clogs the surface. Always use water. If I had to clean oil out of one, I would probably boil it in lye.
Paul K. Dickman
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'Sounds good, if you have one of those tools. I'm curious, though, about what happens when you use the traditional emery-cloth method with Arkansas stones. Maybe I'll try it with one of my old slips, just to see.

The stories about sharpening stones and how to use them seem to have a lot of variations. I've used honing oil or straight kerosene on mine for decades without any clogging. I just flood them after use and wipe them off, as I mentioned. I've been told never to use anything but light oil or kero on oilstones, including novaculite stones, so I guess there's someone around to tell you anything.
BTW, I'd want someone else to try boiling in lye before I tried it on my own stones. It's great for cleaning gun barrels before blueing but Arkansas stones are mostly silica in the form of quartz, and an alkali-silica reaction is well-known to attack and weaken silica. It may be OK on the fairly nonreactive quartz form of silica, but not with my stones, thank you, until somebody else goes first..
-- Ed Huntress
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It should do something, quartz has a mohs hardness of 7 and emery is a 9. The only problem I see, is that dressing a india stone is like dressing a grinding wheel, you just have to break the bond not the abrasive. Cryptocrystaline quartz is bonded a little tougher.
Worst that would happen is that the only thing you'll acheive is cleaning the surface. Any serious flattening would be a a lot of work, though. Starting with a diamond stone be a big help. I have sanded a lot of quartzes and can tell you from experience, it is a lot of work to remove even minor imperfections by hand sanding.

Ha. Probably true. I learned it from my father. It is his 8"x2" hard white I have been using for the last 40 years.

Geez, I'm not talking about dunking it in molten caustic potash. Automatic dishwasher detergent would probably do a fine job too.
Paul K. Dickman
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OK. You go first with the boiling lye. d8-)
-- Ed Huntress
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I forgot to mention what I found to be the best method of cleaning sharpening stones. I dump the stone in my ultrasonic cleaner for a short period of time. After removing the stone from the cleaner I gently heat it with a hand-held heat gun. You can also set them out in the sun on a warm day.
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twolluver gave a good description of how to flatten which will also clean the stone. If the stone is natural it will have no open connecting pores and the glaze will be just on the surface so lapping with 90x silicon carbide grit on plate glass, cast iron, granite tile or any similar flat surface will quickly remove the glaze and flatten. If a lot of lapping is to be done psa mylar will protect the lapping surface and help keep the grit from rolling and crushing. The only truly critical tools that require flatness are chisels. Wide plane irons depending on their use, may also require a truly flat stone. Just a quick revision: two critical elements to a cutting edge, shape and keenness. Shape, dictated by use and materials, extremes are exemplified by a straight razor and a metal cutting tool bit, both may be equally keen, the keenness being determined by the degree of polish on the two surfaces that meet to from the cutting edge.
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Twolluver, Ed, Paul, John, et al...
Thanks for all your input. It's been an interesting discussion and I've learned a few things I didn't know.
I didn't initially go into my own background or experiences 'cuz of a desire to be brief. But I have a fair bit of experience using and dressing stones. I use water stones, India stones or specialized horizontal and vertical low speed sharpening stations to put an edge on my chisels, knives and plane irons. I use whatever technique strikes my mood. I'm sure that I'm like most of you guys here... I've got more "tool toys" than ordinary folks can imagine. I used stones and slips extensively when I was gunsmithing so I'm kind'a familiar with their compositional properties and the intended uses. (I liked the razor blade metaphor... it was very good!)
I've had this black Ark stone for many decades and I'd occasionally consider using it to polish an edge but its surface isn't flat, as I explained earlier. My grandfather didn't have the alternatives I do so he learned how to work the stone in spite of the imperfections. It's still contained within the case he made by hand more than half a century ago. (You can still see tool marks on the wood from the hand auger and chisels he used to make the mortise in each half of the case).
I'd planned to make a carriage to house a sled in which the stone would ride (some conduit or pipe; an aluminum carriage with 8 bearings in a V shape to ride the pipe) that would carry the stone over the carbide cutter of the angle grinder, the grinder firmly secured in relation to the sled. Imagine an inverted surface grinder where the workpiece moves over the cutter.
All your suggestions have merit... and most of you have highlighted the inherent risk, in that I could damage the stone. Maybe I should put it away with my other collectibles and keep it as it is, in granddad's memory. I enjoyed reading your suggestions (and conversations imbedded within the thread).
Cheers
Michael
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On Wed, 02 Jan 2008 18:51:33 GMT, with neither quill nor qualm,

You should be well versed on diamond plates by now. They'll take a helluva lot more abuse and keep on cuttin'.

Very cool.

As brittle as Arkansas stones are, you're better off not doing that.

Yes, suggest you keep it (and the memories) and use it as your grandpa would have, on his pocket knife.
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I actually recall, as a wee lad some fifty odd years ago, him riding his foot powered whetstone (with me in his lap) sharpening his tools and lubing the stone (20" diameter) with an old soup can attached as a water reservoir. At night he'd hone his wood chisels and straight razors on that stone. I have some of his chisels, (up to 3/4" in width) so I assume he figured out where to work them in a practical way on that irregular surface. O'course he also had 3 leather strops that he'd tie to the door knob to further sweeten an edge... although I only recall him doing the straight razors on the strop. Chisels were probably worked on the strop while on a flat surface.
I'd also thought that prior to setting up a sled for the grinder I might have a go at the stone with my diamond plates or paste compounds on plate glass. I realize now that it was the challenge to flatten this stone that inspired me and made me lose focus on its sentimental meaning to me. So I'm going to leave it alone. If I find an orphaned stone in similar condition... I'll try playing with it instead.
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Find a grandkid or neighbor kid about 3 or 4 who owns a tricycle. Design a nice wooden frame slightly larger and thicker than the stone with an eye bolt in one end. Find an appropriate rope to tie the box to the little guy's tricycle. Go to a large plot of fairly flat concrete, a tennis court works quite well. Bring along a folding chair, sodas for the kid, and a few cold ones for yourself. Insert stone in box, kid on trike, rope between, open cold one, sit back and watch.
Check progress on stone at the end of each cold one. May require more than one kid for hard black Arkansas. May require more cold ones to insure proper supervision. You can install a weight on top of the stone and water on the concrete, especially if it's summer.
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On Wed, 02 Jan 2008 03:23:27 GMT, "toolman946 via CraftKB.com"

I looked back at some notes from my violin makers discussion group. Some violin makers use Belgian stones, another naturally occurring stone. One person mentioned flattening his stone on his belt sander. I believe Belgian stones are softer than Arkansas, but I don't have personal experience for comparison.
RWL
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On Jan 3, 7:11pm, GeoLane at PTD dot NET <GeoLane at PTD dot NET> wrote:

Have a Belgian stone, it's a LOT softer than even a Washita. More like a water stone. One of the granddads had it, center is about 1/2" lower than the ends. Used for sharpening straight razors.
I'd be very reluctant to do anything dry and powered to a hard Arkansas stone, wet lapping on a diamond wheel, maybe. Lapidary shop would be my first stop, they were shaped that way to start with.
Stan
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On Wed, 02 Jan 2008 03:23:27 GMT, "toolman946 via CraftKB.com"

a time honoured method of resurfacing an oilstone, I've used it a number of times, is to take a standard clay house brick and a domestic garden hose. trickle a small stream of water over the house brick while you rub the surface of the house brick with the old oilstone surface. you will really smooth out the housebrick and in the process you will achieve a perfectly flat oilstone. the method uses the water stream to prevent the clay brick from clogging. I have rejuvinated a number of old oilstones this way and the process achieves creditable results. If the oilstone isnt actually flat after a good rubdown I can tell you that I havent detected any imperfections. The rejuvinated stones work like new again.
I know that the method is awfully low tech but believe me it works. Stealth Pilot
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On Fri, 04 Jan 2008 21:52:52 +0900, Stealth Pilot

<snip>
For the opposite approach, I wonder if a seal shop could do it (well, probably could but probably wouldn't). If you could sneak it on their diamond vibratory lapping table, it'd come out flat to a ridiculous precision.
Pete Keillor
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Gerry wrote:

Right. I haven't done this but saw a video on Youtube or somewhere about knife sharpening and this is what the guy said to do. Randy
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toolman946 via CraftKB.com wrote:

Sure. Oil well, and rub on a carborundum stone that is relatively flat. I think the carborundum stone will wear down a lot quicker than the Arkansas. I have lapped a bunch of bench stones of various types back to flatness this way. You have to watch the shape of the stones, and flip end to end frequently, and due to the difference in hardness you may still end up with a curvature. By controlling the pressure at the ends or center, you can somewhat control where the stones are wearing down. The idea is to use a LOT of oil, so the stones are not grating against each other, but an abrasive-loaded oil film is doing most of the work.
Jon
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