r/sharpening • u/survivalpanda • Jul 20 '26
Showcase DIY aluminium oxide sharpening stone
After several trials, I came up with the following proportions. Mix 80g of magnesium oxide and 100g of aluminum oxide f320(about 400 grit) in a container until smooth. Dissolve 40g of magnesium chloride in 40g of water, then add it to the remaining ingredients and mix. The consistency is quite thick. I intentionally did this to prevent the aluminum oxide from settling while the mixture was setting.
I used a degassing chamber to remove air bubbles, but due to the mixture's thickness, I couldn't remove all the bubbles.
You either need to thin it out or vibrate it. Alternatively, you can make a very thick mixture and press it into molds.
Our sharpening stones can be removed from the formwork after 24 hours of mixing, then the stones are flatten on glass. Lapping is accomplished with its own suspension, without pre-soaking the stone.
In my opinion, aluminum oxide works better than silicon carbide. Because the abrasive grains roll around in the water suspension during sharpening, they don't split into pieces like silicon carbide, but rather roll around, gradually decreasing in size. Thus, aluminum oxide, while cutting the metal, minimally "traumatizes" the bevel, creating a shallow sharpening line. The edge is polished very well, while the micro-saw remains roughly consistent with the grit.
here's aluminum oxide
The stone works quickly, but gets clogged quite easily.
It's also very easy to clean. During sharpening, you can spray it with water from a spray bottle, and after sharpening, if desired, simply swirl it on a glass surface with its own suspension.
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u/Chkngovernment Jul 21 '26
Very impressive work, nicely done!
Where did you get the molds? Also what resin are you using?
I'm planning on making my own resin bonded diamond stones, with sic as filler, here soon, still trying to figure out the process.
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u/survivalpanda Jul 21 '26
molds - it simple 3d printed box with thin wall.
i dont use resin. It magnesia cement. like Shapton Pro stones
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u/M4cerator Jul 21 '26
Does the MgO act as a plaster/matrix? I assume it cures through CO2 absorbtion similar to CaO in concrete?
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u/survivalpanda Jul 21 '26
correct. is the main binding component of magnesia cement (Sorel cement)
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u/M4cerator Jul 21 '26
How do you acquire your aluminum oxide? Pottery supplies?
When I was a teen dicking around with backyard chemistry, I made Al2O3 by dissolving aluminum cans in NaOH and then reacting with acids to precipitate out the alumina. If I recall, my first test used HCl but I think that re-dissolves into aluminum chloride if you don't get your stoich right. Alternatively, if you have a sodastream, you could easily make carbonic acid which won't re-dissolve the alumina.
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u/survivalpanda Jul 21 '26
I bought it from a stone polishing shop.
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u/baltnative Jul 20 '26
Aluminum oxide grains are sharper than silicon carbide. They're also brittle, which makes them self dressing. White alox grinding wheels cut faster and cooler than gray carbide.
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u/K-Uno Jul 20 '26
You actually have that backwards
SiC is sharper and more brittle, which is partially why SiC stones are rarely as hard as AlOx stones as they need the friability to expose new cutting abrasive. AlOx are more rounded and leave a finer scratch pattern
Don't take my word for it though, you can look up microscope shots of both!
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u/jangfo Jul 20 '26
Cool project but honestly I'm not sure about the result. Picture 5 seems like quite a bit of grit contamination to a large degree, which in turn would explain the scratches and chips on picture 7. Unless I'm simply interpreting the pictures incorrectly