Ruby Sharpening Stones

J

jeffbird

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Feb 3, 2011
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740
What are ruby sharpening stones used for?

Manufacturers say they are second in hardness to diamond plates.

Congress Tool, among others, offers them, so there must be some professional tool and die makers or machinists using them for some application.
 
I use them to sharpen knives and engraving tools. The finest ones will leave a mirror finish.
 
'Ruby' is aluminum oxide, of which its hardness will be essentially similar to any other aluminum oxide abrasive. They all measure around 2100-2300 on the Knoop hardness scale, as compared to abrasives like silicon carbide (SiC) at around 2600-2800 Knoop, cubic boron nitride (CBN) at something over 4500 Knoop, and then diamond at 7000 Knoop as the reference for the hardest of all. I attached a comparative hardness chart from Norton below.

Other factors like toughness, friability (tendency to fracture, or the breaking down of abrasive grains), and grain shape can make different forms of aluminum oxide either much more aggressive for heavy grinding, or somewhat gentler and more finessed for polishing.

ikmPGGr.jpg
 
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As I said, I use the ruby stones to sharpen/polish the tips of my gravers. They are used for engraving metal.
Some of the new knife steels are difficult to sharpen and require diamond stones or coarse AO stones like India stones to get an edge.
The sintered fine ruby stones will polish those edges easily.
 
I have had some weird experiences with very coarse ruby stones :
My first 60 grit ruby is at work and not sure what is printed on the back of it but an identical one I ordered years later to have at home says on the back : Boride Ruby Series 60 and is a Gritomatic . They are super inexpensive for a super coarse stone ; I will give 'em that .

First one I bought cut pretty good the first few minutes but after rinsing the swarf off in water it would get crumbly and have rocks rolling around all over it to where I didn't feel like I was accomplishing anything but rolling rocks around under a knife .

The second one does not act like that . When new they both cut fast but that aggressiveness died pretty fast .

Sure I started out using oil with the first one .
let me say this again here : I HATE USING OIL ! can't rinse the stone . Dabbing at it with a rag, especially with these coarse bastards leaves fibers of the rag all over the stone .
I HATE USING OIL !

After years of infrequent use the first one no longer looses grit like that when rinsed with water . Don't know . . . maybe it finally "cured".

One cool thing was ; while I was reprofiling a knife . . .every time I would lightly touch the plunge grind during a stroke I would get a very clear SPARK 💥
That was fun !
I find there are many better stones for reprofiling .
I'm not one to be busssing out the carborundum grit to recondition my stones ; maybe a quick flattening on a diamond plate every blue moon .

It seems like I recently saw some fine ruby stones for sale but I have an embarrassing collection of stones (for the Edge Pro ; that's what I am talking about) . . . ha ha ha I was looking longingly at one of those mottled green natural finishing stones that is similar to a 10,000 stone . . . don't need it though .
 
Obsessed with Edges said:
as compared to abrasives like silicon carbide (SiC)
Click to expand...
yes that was what I was thinking when talking next down in hardness to diamond / CBN . That is readily available to us for sharpening .
You guys finally taught me that "ceramic" is not harder than some steel knives (well at least not the carbides in the blades ) .
I'm a believer now .
 
Wowbagger said:
I have had some weird experiences with very coarse ruby stones :
My first 60 grit ruby is at work and not sure what is printed on the back of it but an identical one I ordered years later to have at home says on the back : Boride Ruby Series 60 and is a Gritomatic . They are super inexpensive for a super coarse stone ; I will give 'em that .

First one I bought cut pretty good the first few minutes but after rinsing the swarf off in water it would get crumbly and have rocks rolling around all over it to where I didn't feel like I was accomplishing anything but rolling rocks around under a knife .

The second one does not act like that . When new they both cut fast but that aggressiveness died pretty fast .

Sure I started out using oil with the first one .
let me say this again here : I HATE USING OIL ! can't rinse the stone . Dabbing at it with a rag, especially with these coarse bastards leaves fibers of the rag all over the stone .
I HATE USING OIL !

After years of infrequent use the first one no longer looses grit like that when rinsed with water . Don't know . . . maybe it finally "cured".

One cool thing was ; while I was reprofiling a knife . . .every time I would lightly touch the plunge grind during a stroke I would get a very clear SPARK 💥
That was fun !
I find there are many better stones for reprofiling .
I'm not one to be busssing out the carborundum grit to recondition my stones ; maybe a quick flattening on a diamond plate every blue moon .

It seems like I recently saw some fine ruby stones for sale but I have an embarrassing collection of stones (for the Edge Pro ; that's what I am talking about) . . . ha ha ha I was looking longingly at one of those mottled green natural finishing stones that is similar to a 10,000 stone . . . don't need it though .
Click to expand...
The "sparks" are actually ONLY light! It's what's known as "triboluminescence" and is the same dynamic as what makes "sparks" when you bite a wintergreen Lifesaver candy in the dark! We...don't really know how it works, exactly, but some ruby exhibits it as a quality, as does some quartz, among other materials. No heat, just light!
 
FortyTwoBlades said:
The "sparks" are actually ONLY light! It's what's known as "triboluminescence" and is the same dynamic as what makes "sparks" when you bite a wintergreen Lifesaver candy in the dark! We...don't really know how it works, exactly, but some ruby exhibits it as a quality, as does some quartz, among other materials. No heat, just light!
Click to expand...
Weirder and weirder .
:thumbsup:
 
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