Preyda stones are not flat (flatten a fine stone??)

[Andrew Pitonyak]

Some years back I purchased a set of Preyda Arkansas stones for a friend but he never used them (or more accurately never had time for me to teach him to use them) so they sat in a box unused. I finally opened them and used them.

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For many reasons I really wanted to like this set of stones but I had trouble getting consistent results... And then I thought "is that corner low?" It turns out that two of the three stones are not flat. The finest stone, the "Black Hard" is out of flat on both sides. The stones are out of flat along both the length and the width, which means that it takes a lot of work for me to get results. The Soft stone is flat on one side, but not the other. The Hard stone is flat on both sides. If I had not figured this out years after purchase I would just take it back (WoodCraft has great support and a nice return policy). After a few years, it is on me for not checking.... But I have never checked a new stone for flat. On a whim, I went back and checked some of my other stones, which means that I checked about 35 stones. Every stone I could access (some are still shrink wrapped), was flat except for one heavily used Washita stone purchased off eBay. OK, many of my Washita stones were purchased off Ebay and I flattened the stone that was not flat. So all of my Norton, Best, and Dan's stones were all flat when purchased new.


Previously I have only checked used stones for flat. Two out of three stones out of flat. I do like the packaging and the form factor, something that is nice to keep at the office when I want to mindlessly do something while killing time.

I have only flattened Washita stones, never a Hard Black. I remember some advice related to Washita stones that recommended dressing the two primary sides with different grit Silicon Carbide crystals because the roughness affects the scratch patterns supposedly. I have never tested any of this, but i do have many different grits of Silicon Carbide crystals I can use. I expect that this would be rather pronounced with a "Hard Black" stone, which is pretty fine. Kind of a waste of time if I need to then polish the stone. I might do it just to do it, but how annoying.

I need to remove between 0.5 mm and 1 mm to flatten; closer to 1 mm.

I assume that most of you were smart enough to check your stones for flat.

[Cameron Wood]

I would use #120 wet/dry sandpaper on a flat surface, with water. Finish by lapping the stones against each other, also with water.

Some elbow grease, but not a big deal.

[Rafael Herrera]

I flatten washitas with 90x grit SiC powder and leave it at that. The same could be done with your soft ark.

Use a finer grit for the harder stones, but it may take more time to get them flat.

Use a fine grit to get the roughness out of the hard ones but not too much since you don't really want to polish them.

[les winter]

Dan's will flatten stones of any manufacturer for a modest price.

[Andrew Pitonyak]

Dan's will flatten stones of any manufacturer for a modest price.

Interesting, that had not occurred to me. I will admit, however, that I considered just replacing the out of flat stones with Dan's stones since I own a bunch of them, including some stones that are the same size. I considered building a similar box to house a set from either Dan's (most of my stones are from Dan's) or from Best (I have a few sets of different sizes).

I will do a bit of work and respond back.

[Rafael Herrera]

Dan's will flatten stones of any manufacturer for a modest price.

That doesn't make a lot of sense to me. If one has the lapping grit, the whole things takes about 15 minutes or less.

[les winter]

Depends how out of flat the stones are and how flat the substrate is. When I had the same issue, the cost of the flattening by Dan's was less than the postage. Nothing wrong with doing it yourself. In my case, after 1/2 hour of trying, I gave up.

[Rafael Herrera]

I don't know if you've ever tried silicon carbide grit, but before using that I saw recommendations to use sand paper, concrete blocks diamond stones, etc. I tried some of them, they all are orders of magnitude slower and ineffective compared to sic grit. It really doesn't take much on most stones: arks, washitas, indias, crystolons, slates, etc.

[Andrew Pitonyak]

I started with 80 grit

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After about 10 minutes, the soft stone was sufficiently flat that I called it good. You can see some progress with the 80 grit.

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Things were going so slowly that I switched to 45 grit. An hour later I simply gave up. Both sides are out of flat and it is still out of flat. I don't think that Preyda stones are not worth the trouble I think. I would want to flatten both sides and then polish both sides. Makes more sense for me to just deal with the stone from the 1/2" side and use it to sharpen knives with a concave type blade (or just throw it away).

Clearly I made some progress, but I am still out on both ends of the stone and I have not touched the other side.

Dan's rates their stones ass Medium (soft), Fine (Hard), Extra Fine (True Hard or Translucent), and Ultra Fine (Black).

In the 6x2x1/2 size I have a Medium, Fine, two Translucent stones, and (in theory) two Ultra Fine stones. I think that one of my Ultra Fine stones is with my chip Caving stones. My "Best" stones are mostly 10x3 and 8x2, and my other Dan's stones are mostly 8" x 3" and 10" x 3" stones. So if I want to keep a set in the existing packaging I could make that happen, or, I could just build another box.

In the meantime, I will likely just avoid Preyda stones in the future.

[Jim Koepke]

I also have one of the three stone sets from Woodcraft. They haven't seen much use in the past 20 years.


Dan's rates their stones ass Medium (soft), Fine (Hard), Extra Fine (True Hard or Translucent), and Ultra Fine (Black).

My Dan's stones are the same, though my translucent are slip stones and other small stones. The Medium (soft) is not as soft as I would have hoped. Some of my other stones were purchased as Washita stones or have a similar action to a Washita.

My Dan's Fine (Hard) and Ultra Fine (Black) Arkansas stones have been great in my switch to using mostly oilstones.

jtk

[Andrew Pitonyak]

I don't know if you've ever tried silicon carbide grit, but before using that I saw recommendations to use sand paper, concrete blocks diamond stones, etc. I tried some of them, they all are orders of magnitude slower and ineffective compared to sic grit. It really doesn't take much on most stones: arks, washitas, indias, crystolons, slates, etc.

Yeah, that is what I used. It was not working well with the Hard Black stone. I have only used it previously on Washita stones. It was fast for the Soft stone as well. Sadly, the Hard Black was the worst of the bunch. Also, the Hard stone is high in the middle, which (in my experience), is the most difficult to flatten (because the stone will rock),

[Andrew Pitonyak]

Jim,

Is your set of three flat? 2 out of 3 out of flat feels very bad. I sent an email to Preyda but they did not get back to me. When I had questions for Dan's, they were immediately responsive to my questions. Of course, I never had a problem with a stone from Dan's. They cost more but I perceive them as better than the rest, not that I am sufficiently good to know if this is correct.

I expect the same high quality from Norton (by the way). Not had any complaints about my stones from Best, but I use my Dan's stone more.

[Derek Cohen]

I flatten washitas with 90x grit SiC powder and leave it at that. The same could be done with your soft ark.

Use a finer grit for the harder stones, but it may take more time to get them flat.

Use a fine grit to get the roughness out of the hard ones but not too much since you don't really want to polish them.

Raf, I am not disputing what you do here, but have a question about the use of the finer grit …

It has long been a puzzle for me why some recommend coarse grits to flatten stones at the coarser end of the spectrum, and finer grits for stones at the finer end of the spectrum. The point is, as I believe, the result in honing comes from the grit in the stone and not the surface treatment of the stone.

I use the same coarser grit (140 diamond stone) to maintain all my waterstones. In the case of these oil stones I would use the 90 grit SIC powder or the diamond equivalent.

Regards from Perth

Derek

[Warren Mickley]

Raf, I am not disputing what you do here, but have a question about the use of the finer grit …

It has long been a puzzle for me why some recommend coarse grits to flatten stones at the coarser end of the spectrum, and finer grits for stones at the finer end of the spectrum. The point is, as I believe, the result in honing comes from the grit in the stone and not the surface treatment of the stone.

I use the same coarser grit (140 diamond stone) to maintain all my waterstones. In the case of these oil stones I would use the 90 grit SIC powder or the diamond equivalent.


I sounds like you have never learned to use an Arkansas stone. The finer stones have finer crevices. If you cut coarse crevices in a fine stone, the crevices will do the cutting and the stone will not polish as it should.

[Derek Cohen]

Warren, I have never used an Arkansas stone. Hence my question.

Regards from Perth

Derek

[Andrew Pitonyak]

I sounds like you have never learned to use an Arkansas stone. The finer stones have finer crevices. If you cut coarse crevices in a fine stone, the crevices will do the cutting and the stone will not polish as it should.

I am really annoyed that I cannot find the original link AND I did not document it as I am prone to doing, so.... <sad face> :mad:

In my mind, it was something at Tools For Woodworking (Gramercy), but at this point I think I was wrong.... But who ever it was, they were selling Washita stones and advocating that you would dress your new stones so that one side was finer and the other side coarser. I even saw someone selling one on eBay that had been prepared that way and then never used.

If I remember, the finer side left a smoother surface. For sure, this Hard Black stone that I was running on a coarse SIC is much rougher to the feel and there is no way it will leave a smooth surface even if the only reason is because it will not have a consistent smooth surface so the scratches will not be uniform and tight together. Unsure who that would translate into faster metal removal.

With my water stones, the binder is soft compared to an Arkansas stone. I would expect, therefore, that any rough surface would then wear down pretty quickly off a water stone. But I am unsure about that.

[Jim Koepke]

Jim,

Is your set of three flat? 2 out of 3 out of flat feels very bad.
…
I never had a problem with a stone from Dan's. They cost more but I perceive them as better than the rest, not that I am sufficiently good to know if this is correct.
…


I have never really checked them. They didn't rock in use.

I'm very happy with my Dan's stones and do not regret the cost of ownership.

jtk

[les winter]

Dan's flattening prices from 2019

11 ½ x 2 ½ x ½ Black, $18.77
11 ½ x 2 ½ x ½ Translucent $24.37
Plus shipping.

[Rafael Herrera]

Raf, I am not disputing what you do here, but have a question about the use of the finer grit …

It has long been a puzzle for me why some recommend coarse grits to flatten stones at the coarser end of the spectrum, and finer grits for stones at the finer end of the spectrum. The point is, as I believe, the result in honing comes from the grit in the stone and not the surface treatment of the stone.

I use the same coarser grit (140 diamond stone) to maintain all my waterstones. In the case of these oil stones I would use the 90 grit SIC powder or the diamond equivalent.


The coarser grit will cut more aggressively, so the process is faster with them. The grit breaks down fairly quickly, so even if you start coarse, one ends with a finer slurry until you refresh it with fresh grit.

I suppose finer grits are preferred with finer stones because otherwise the surface would be left all scratched up. I should point out that on softer stones than a typical washita, using the coarse (around 90x) grit leaves a very rough unusable surface, in my case they were a slate, and some waterstones. After the coarse grit, I used finer grits until a uniform surface was achieved.

I have about a couple dozen sharpening stones, mostly washitas. The fine ones are Arkansas (Dan's and Norton) and those came my way in good shape, so I didn't need to lap them. Some of the washitas, indias, crystolons arrived in need of some lapping. The infrequent need to flatten and trying to wear them evenly is one of the reasons I prefer the washitas and the Indias over water stones.

Maintaining oilstones or waterstones with a diamond stone should work, the amount to remove is small compared to what's needed when they're dished or clogged. It's in that case where the coarse grit saves you time.

There's one last point to be made. Once you start using a relatively low wear oilstone like an India, washita or an arkansas, the roughness left from the manufacturer's lapping or your own refurbishing lapping wears off. I think they say that the stone "has settled". It's around that cutting power that one works with when using these stones, not their behavior freshly lapped. One could rough them up with a coarse stone, but that just adds time to the process and may not be needed.

[Rafael Herrera]

I am really annoyed that I cannot find the original link AND I did not document it as I am prone to doing, so.... <sad face> :mad:

In my mind, it was something at Tools For Woodworking (Gramercy), but at this point I think I was wrong.... But who ever it was, they were selling Washita stones and advocating that you would dress your new stones so that one side was finer and the other side coarser. I even saw someone selling one on eBay that had been prepared that way and then never used.


TFWW had a limited run of Norton (supposedly) Lily White Washitas a while ago. Production of those stones was discontinued by Norton.

I don't know where this advise came from. My personal opinion is that it's nonsense, once the stone settles, there will be no difference between sides unless you lap the stone periodically. That sounds to me like a good way to waste away the stone.

If you lean on the tool hard, the washita will cut aggressively. If you lean on the tool less hard, it will polish. You feel in your fingers the grinding action of the stone.

[Rafael Herrera]

I started with 80 grit

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After about 10 minutes, the soft stone was sufficiently flat that I called it good.


I don't know if the amount of grit you're using is counterproductive or not. I use a very small amount in comparison. A typical lapping session of an old washita looks like this. Once the slurry becomes too fine I add a similar amount as in the middle picture. A large amount of grit won't form a flat grinding layer. The first and last pictures are a before and after look. The stone wasn't terribly dished, but it wasn't flat. The whole thing took about 15 minutes.

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Regarding your hard arkansas, if they're bellied, they may not be that easy to lap. Just rubbing them on the plate might wear the highs and lows and you will be chasing your tail. Localized pressure on the high area might help. I really don't know.

Another consideration is that since these stones were meant as a knife sharpening kit, flat or bellied really makes no difference if they're going to be used for that purpose.

Bench sharpening stones need to be flat.

[Robert Hazelwood]

Do whatever you need to do to get it acceptably flat. Then wear in the new surface by lapping some chisel or plane iron backs on it. Very hard or high wear resistance steels would be ideal to speed up the process.

Anyways, I think you'll find that most of the roughness comes out pretty quickly, and then it will slowly get finer with use.

[Andrew Pitonyak]

I never knew how much grit to use. If I want to remove the belly I need to have just a small concentrated area of grit and then push just the belly through the grit, which has proven to be difficult at best, Would be easier with less grit. Given that I paid about $50 for the set of three stones, it is not worth the time to finish trying to flatten the black stone; it is pretty far out of flat on both sides.

The stone is not even flat width wise with a dip one corner. There is a lot wrong with this stone. I just wish I had noticed earlier. This did convince me to go back over my other stones and take a look.

I took another try at the Preyda Black Hard. The Soft was not as far out and it had waves across the width and lengthwise it was not as far out as the black. No clearly defined belly, at least not a large one.

[Jimmy Harris]

For a really bad stone, I just mark up the stone with a pencil and then find a fairly flat slab of concrete at my house and grind the stone on my porch or driveway, while running water from a hose. I use a random pattern to compensate for any deviations in the concrete. Then just keep going until the pencil marks are all gone. Having a giant surface makes it a lot easier and quicker to work because you can take much longer strokes. It still takes a while though.

If the stone isn't too bad, I have a flattening stone to bring it back to true. The flattening stone is the way to go because it's a little more accurate and easy to work with, but if you're having to remove a ton of material, you'll likely put a warp in that stone before you get your initial stone flat.

[Andrew Pitonyak]

Preyda finally got back to me. I guess my message was bounced around. Preyda said "send the not flat stones, we will flatten them, and send you another stone for your trouble".

I absolutely did not expect that. I told them that i already flattened one and that I tried to flatten the other. They may not want it after I roughed up one side, but will see. I was not expecting the response. Good on them!

[Andrew Pitonyak]

I sent the three stones back to Preyda. The state I sent them? One was completely flat out of the box. One was flat because I flattened it. The Black hard was not flat when I received it and it was not flat when I sent it to them. In fact, I had simply made the stone thinner and not flat. It is really difficult for me to remove the belly of an Arkansas stone.

So what did Preyda send back to me? I sent them three stones and they sent back four stones. All of the stones were received as dead flat based on my tools (which means better than 0.001" because the straight edge I used is listed as 0.001" over 12").

I sent them a Soft, Hard, and Black Hard. I received all of these back and a Surgical Black. Preyda claims that this is their finest stone

see

https://sawmillcreek.org/showthread.php?276528-Preyda-Arkansas-Stones


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The stone is 1/2" thick but the box allows for a much thicker stone. Part of me thinks that this is smart (same box for all stones of similar dimensions ignoring thickness) and part of me is annoyed because the stone can move around top to bottom.

If you look carefully you will see magnets that do a great job holding the box shut. I am ashamed that I never thought of doing this. The magnets work really well and are a nice touch.

This next photo shows that the stone is sitting in a rubber thing in that box. This means that the box is wider than the stone. This rubber bit works really well at keeping the stone from sliding in use. A pretty nice touch. I am pretty impressed with this.


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I am really pleased with these stones and I am impressed that Preyda replaced all the stones, even after I had clearly messed with one of them. And, they threw in one of their best stones to say sorry for the trouble.

[John C Cox]

Glad to hear they took care of you. I've wondered quite about their "Arkansas water stones" and whether they were any good.

[Andrew Pitonyak]

If you live anywhere near the middle of Ohio, you can try preyda, Dan's, best, and maybe some others.