Sharpening Question - Aluminum Oxide Powder

[Richard Niemiec]

I've heard of folks using aluminum oxide powder in a water slurry to do some sharpening on flat plates, and also to lap plane soles. I've found some sources for pound lots at about $15/lb, but the question is what size, as they sell in micrograms (um). Anyone have experience with this? My choices are 3, 5, 9 or 15 um. Thanks in advance. RN

[Eddie Darby]

The um with the extension on the front of the u below the bottom of the letter, from the Greek alphabet for the letter 'mew', stands for microns, which is 1/1000 of a millimeter. A human hair is about 40 microns thick. A Japanese 8,000x grit waterstone has a particle size that is about 1.2 microns.

Here is a chart that gives some of the particle sizes:

http://users.ameritech.net/knives/grits.htm

I like your selection and would add a few more.
For lapping, I would want to use a grit in the area of 50 microns, to speed up the initial stages of lapping, and 30 microns to follow that.
I would also add 1 micron in size for final honing.

[Mike Henderson]

Try these people (http://www.abrasivedepot.com/ad/mss/mss-wp.nsf/WebEngine?OpenAgent) for the Al Oxide power. They offer 3 pounds for $15. You might also consider the silicon carbide.

Mike

[Richard Niemiec]

Great information. The chart is very helpful Eddie, and Mike, thanks for the vendor info.

RN

[Michael Fross]

I've always used Silicone Carbide for lapping. Is there an advantage to Alum. Oxide?

Also, thanks for the great link. I've been buying from Lee Valley and while they are great, $15 for 3 lbs is a good deal.

Regards,

Michael

[Mike Henderson]

Richard - The finest grit that Abrasive Depot carries is 50 micron. I notice that your source has grits much finer - which accounts for the higher price. Would you post the URL of the place that you found, please?

Mike

[Richard Niemiec]

Its a scientific supply house, VWR followed by a dot com. When you get there do an internal website search for "aluminum oxide powder." They have specialized stuff down to 1 micron, pricey for that level of fineness, however.

RN

[John Schreiber]

So, what's the advantage of using this slurry instead of adhering abrasive paper to the glass? Does it also wear away the glass itself?

It sounds like an interesting idea, but it seems that you would have to lap a whole lot of plane bottoms to make it cost effective.

[Richard Niemiec]

Well, its for sharpening as well, simply using the abrasive slurry in place of any other abrasive. I don't know more, simply because I have not gotten any of the abrasives, but for $30 or so it's another method.

rn

[Don Naples]

I've always used Silicone Carbide for lapping. Is there an advantage to Alum. Oxide?
Michael: Silicon carbide is not the best choice for use with ferrous metals as it breaks down so quickly it is difficult to achieve any abrading before it turns to dust and polishes the metal. Aluminum oxide is a better choice for sharpening and abrading steel tools.
Silicon Carbide - A synthetic abrasive discovered in the late 1800s, which is harder than aluminum oxide. Used in green and black forms, which are distinguished by levels of purity, silicon carbide is typically applied to nonferrous applications. The sharp and easily fractured abrasive grains are also used in nonmetal applications such as the wood and leather industries.
Don Naples
Manufacturer of the Lap-Sharp

[Eddie Darby]

This trick has worked for me in the past: I have put the loose particles onto a sheet of wet/dry paper, which is all on a granite surface plate. I find that the wet/dry paper protects the granite surface and the particles stay in place, cutting aggressively. I make sure that everything is fairly wet with a spray bottle.

[Michael Fross]

Michael: Silicon carbide is not the best choice for use with ferrous metals as it breaks down so quickly it is difficult to achieve any abrading before it turns to dust and polishes the metal. Aluminum oxide is a better choice for sharpening and abrading steel tools.


Thanks Don. I didn't know that. I'll have to use Alum. Oxide next time I need a refill. However, I find that I mostly use it for flattening my waterstones, but I have lapped the bottom of my planes with it.