Sintered Ruby As A Replacement Material For The Sharpmaker Ceramic Triangles

vorpalblade · Feb 22, 2015

SpeedHoles said:
I might just drop the money and get myself some diamond rods and see how long they last instead of experimenting.

If you could get good quality, extra fine diamond rods, they should be much less frustrating to clean than the original ceramic Sharpmaker stones.

Thomas Linton · Feb 22, 2015

dr_fosg8 said:
Speaking of links there is one in the op too.

Sorry if showing the op options that would work for the sharp maker that are not ceramic has in some way upset you. He was specifically talking about the sharp maker.

As to the questions of hardness and cutting ability of the stones I have no idea.

Carry on and good day.

If someone is "upset," it's not me. Just curious.

And I have never used any sharpening machine so I have absolutely no vested interest in them one way or another.

Lagrangian · Feb 22, 2015

My understanding is that "ceramic" sharpening stones are based on aluminum oxide.
Ruby is also aluminum oxide, as is sapphire.

http://en.wikipedia.org/wiki/Ruby

There are lots of additional effects such as how the aluminum oxide is processed and sintered. My guess is you're seeing improvements in these types of effects, rather than "ceramic" vs "ruby."

vorpalblade · Feb 22, 2015

Lagrangian said:
My understanding is that "ceramic" sharpening stones are based on aluminum oxide.
Ruby is also aluminum oxide, as is sapphire.

http://en.wikipedia.org/wiki/Ruby

True. All three are based on aluminum oxide.

There are lots of additional effects such as how the aluminum oxide is processed and sintered. My guess is you're seeing improvements in these types of effects, rather than "ceramic" vs "ruby."

Not "ceramic" vs "ruby" but ceramic vs sintered ruby. Whatever the nomenclature, sintered aluminum oxide is the only 100% version of AL2O3. That's what gives it better performance as a sharpener.

Bill DeShivs · Feb 22, 2015

I just ordered a couple of the cheap Chinese ruby stones. I'll let you know how they compare to my Gesswein ruby stone.

vorpalblade · Feb 22, 2015

Please do. The comparison will be interesting.

Fanglekai · Feb 23, 2015

vorpalblade said:
If you could get good quality, extra fine diamond rods, they should be much less frustrating to clean than the original ceramic Sharpmaker stones.

I find the Sharpmaker ceramic stones very easy to clean. I get Barkeeper's Friend powder (not the liquid) from Walmart for about $2 for a canister. I use the coarse side of a dual-sided sponge, get it wet, add the powder to make a paste, and then I scrub the Sharpmaker rods. I let the residue sit on the stones for 15 minutes or so for the oxalic acid to do its work. After that it's another quick scrub and rinse and they're good to go. If I'm in a hurry I just scrub and don't bother waiting the 15 minutes. They always cut much better afterwards.

Lagrangian · Feb 23, 2015

vorpalblade said:
Not "ceramic" vs "ruby" but ceramic vs sintered ruby. Whatever the nomenclature, sintered aluminum oxide is the only 100% version of AL2O3. That's what gives it better performance as a sharpener.

Oh... I thought that many/most "ceramic" sharpening stones were just sintered aluminum oxide. So I think you're saying that many are not purely aluminum oxide, and have significant amounts of other stuff in them?

singularity35 · Feb 23, 2015

Lagrangian said:
Oh... I thought that many/most "ceramic" sharpening stones were just sintered aluminum oxide. So I think you're saying that many are not purely aluminum oxide, and have significant amounts of other stuff in them?

Some have unicorn horn and fairy dust in them.

Lagrangian · Feb 23, 2015

I'm a little confused by the claim that the sharpening rod has a "knoop hardness of 20,000." From what I understand, diamond has a Knoop hardness of approximately 7,000 (varies depending on crystal axis).

I think the 20,000 is a just typo, and they mean 2,000. In the chart, you can see that corundum (aluminum oxide) is approximately 2,000 on the Knoop scale.

http://en.wikipedia.org/wiki/Knoop_hardness_test

hank_rearden · Feb 23, 2015

more to the point, ruby and other aluminum carbides are softer than chromium, silicon and vanadium carbides. being "softer" doesn't mean it can't sharpen knives with those carbides included. there are just better ones.

Lagrangian · Feb 23, 2015

I think you meant "aluminum oxides" rather than "aluminum carbides"? I don't think there is a significant amount of aluminum chemically bonded to carbon (aluminum carbide) in these abrasives.

http://en.wikipedia.org/wiki/Aluminium_carbide

The Deacon · Feb 23, 2015

MSRP for a set Spyderco's diamond sleeves for the Sharpmaker is $80, as is the MSRP of their new CBN Sharpmaker rods which are described as the next hardest thing to diamond. At least one BF dealer has them for under $50. That ruby file you use for reference costs $68. Have to wonder how much less a pair of Sharpmaker rods made of that material could be sold for, or how much better they would be for a similar price.

Obsessed with Edges · Feb 23, 2015

Lagrangian said:
I'm a little confused by the claim that the sharpening rod has a "knoop hardness of 20,000." From what I understand, diamond has a Knoop hardness of approximately 7,000 (varies depending on crystal axis).

I think the 20,000 is a just typo, and they mean 2,000. In the chart, you can see that corundum (aluminum oxide) is approximately 2,000 on the Knoop scale.

http://en.wikipedia.org/wiki/Knoop_hardness_test

That '20,000' figure threw me, too. Might reflect different units of measure for the same Knoop Hardness test. I have seen references (quoted below) to Knoop hardness measured in different units, creating a different, but similarly arranged scale, with the same proportional differences between listed materials. I see the '7000' figure at the top for diamond more often, with Al2O3 (corundum) usually in the ~2000-2200 range.

Here's an example of a reference to a different Knoop scale, referenced to diamond's hardness @ 70,000 (versus 7,000) and AlOx proportionally measured @ 20,000 on that particular scale:

( text quoted from site: http://www.gearsolutions.com/article/detail/5499/hard-choices-diamond-or-cbn )

"However, while CBN is substantially harder than other conventional abrasives, it has only 64 percent the hardness of diamond--45,000 N/mm2 Knoop, as compared to diamond's 70,000 N/mm2 Knoop. (Hardness of Al-oxide is 20,000 N/mm2 Knoop.) "

David

Obsessed with Edges · Feb 23, 2015

hank_rearden said:
more to the point, ruby and other aluminum carbides are softer than chromium, silicon and vanadium carbides. being "softer" doesn't mean it can't sharpen knives with those carbides included. there are just better ones.

Aluminum oxide is harder than chromium carbides, which are around ~1700-1800 Knoop hardness (on the scale referenced to diamond at 7000). Aluminum oxide is usually around ~2100, give or take (includes 'Ruby' or 'Sapphire' versions of AlOx as well). Chromium carbides usually won't present a problem with any Alumina/aluminum oxide hone, ceramic or not.

David

vorpalblade · Feb 23, 2015

Fanglekai said:
I find the Sharpmaker ceramic stones very easy to clean. I get Barkeeper's Friend powder (not the liquid) from Walmart for about $2 for a canister. I use the coarse side of a dual-sided sponge, get it wet, add the powder to make a paste, and then I scrub the Sharpmaker rods. I let the residue sit on the stones for 15 minutes or so for the oxalic acid to do its work. After that it's another quick scrub and rinse and they're good to go. If I'm in a hurry I just scrub and don't bother waiting the 15 minutes. They always cut much better afterwards.

Call it the laziness factor but my interest is more in sharpening than cleaning. One of the things that impresses me so much about the Sieger sintered ruby rod is that it comes completely clean quickly with soap and water. No special ingredients, no scrubbing, no waiting.

vorpalblade · Feb 23, 2015

Lagrangian said:
Oh... I thought that many/most "ceramic" sharpening stones were just sintered aluminum oxide. So I think you're saying that many are not purely aluminum oxide, and have significant amounts of other stuff in them?

Exactly Lagrangian. Depending on the material, they have binders, fillers and various combinations. With sintered aluminum oxide, you have a pure, dense substance that works in a concentrated way.... It abrades steel fast, losing almost nothing of itself in the process. During sharpening, it loads up but comes completely clean with just a little soap and water.

Fanglekai · Feb 23, 2015

vorpalblade said:
Call it the laziness factor but my interest is more in sharpening than cleaning. One of the things that impresses me so much about the Sieger sintered ruby rod is that it comes completely clean quickly with soap and water. No special ingredients, no scrubbing, no waiting.

Sounds nice. I would definitely like to try those out.

vorpalblade · Feb 23, 2015

Lagrangian said:
I'm a little confused by the claim that the sharpening rod has a "knoop hardness of 20,000." From what I understand, diamond has a Knoop hardness of approximately 7,000 (varies depending on crystal axis).

I think the 20,000 is a just typo, and they mean 2,000. In the chart, you can see that corundum (aluminum oxide) is approximately 2,000 on the Knoop scale.

http://en.wikipedia.org/wiki/Knoop_hardness_test

You are probably correct. My interest in sintered ruby is completely a result of my positive experience when using it.

SpeedHoles · Feb 23, 2015

The Deacon said:
Have to wonder how much less a pair of Sharpmaker rods made of that material could be sold for, or how much better they would be for a similar price.

Those Congress 1/2" ruby triangles are sold for around $10-16 a pair depending on grit choice (probably not including shipping), but the lack of precision on them keeps me away for the time being. I'd imagine a nice precise set actually made for the Sharpmaker would easily sell around $25-30, and I would pay that much.

There is a 180x13mm ruby triangle on ebay that is advertised as fitting the Sharpmaker, but is seems way over priced at $29 for only 1 triangle, putting a pair at much higher price than the Diamond or CBN. And not to mention risk the gamble of it being from China it may be the same thing as the Congress triangle and lack precision (either not fit into base or fitness so loosely that the angle is off).

I am eager to try one for myself though...