Juicing a soft Arkansas stone

[John C Cox]

Hey all,

In the oil stone universe, it seems like soft Arkansas stones don't get a lot of love.

Silicon carbide (Crystolon) and Alumina (India) stones can cut pretty darned fast. So does sandpaper. Then you hit the wall with a super slow cutting soft Ark.

There is a solution.

Lapidary abrasive.

I use the soft arkanas as a substrate for lapidary abrasive. It's sort of the best of all worlds.

I juice my soft Arkansas stones with a pinch of powdered aluminum oxide abrasive, and now, they cut FAST. Best of all, the stuff is cheap - less than $10/lb. I've tried them with both oil and water, and you can use them either way. The feel is fantastic and you still get good feedback from the stone. Oh, and if you want to switch from oil to water, or you don't like it, just scrub it off with dish soap and hot water, and off you go.

Also, if too much gunk builds up on the stone, just wash it off with dish soap and hot water, and off you go.

The only cautions...
1. Don't put this stuff on your super fine black and translucent Arks. You will absolutely hate it. Stick with juicing your soft Ark and you'll be happy.
2. Buy it from an actual lapidary supply. The "Rock tumbling" media on Amazon is poorly graded and doesn't give very good results past the more coarse grits.

Here's a pic of what I ended up with:
6C22EAAA-345E-4A20-A273-7FF7A66C2015.jpg

I use "500 grit" silicon carbide rock tumbling abrasive on my fine India. (That particular stuff came from Amazon and is poorly graded. It is probably closer to 350 grit.). It turbo charges the fine India, but still leaves a fine, uniform scratch pattern that's a bit finer than P1000 sandpaper.

500 grit aluminum oxide actual lapidary abrasive on a cheap, ultra-soft and coarse soft Ark. This stuff is considerably finer than the silicon carbide rock tumbling abrasive stuff. It looks like dust where the SiC looks more like fine sand. This particular stone throws some grit and isn't suitable for anything finer, but it is FAST and amazing with the 500 grit Alumina. Finish wise, it leaves a matte gray haze with a barely discernible scratch pattern.

1-3 micron "Micro-alumina" on a cheap, low-mid density soft Ark that glazes instantly and doesn't cut otherwise. This one leaves a dull mirror finish. On a better quality soft Ark, this polish does not leave fine swirly scratches visible in a loupe, but this particular stone isn't high quality, and throws a bit of fine grit.

"Raybrite A" on a Norton soft. That's a 0.5 micron aluminum oxide polish. The Norton soft is extremely uniform and throws absolutely zero grit. It is a fantastic stone, and this makes it even better. This particular polish mixes better with oil than water, but it still works ok with water, it's just a bit clumpy. This particular stuff leaves a brighter mirror finish when used thick and a more hazy mirror finish when used thinner. This stuff also makes a fantastic strop paste if you want to do that instead of using it on a stone.

Here's a shot of the finish.
DE3C623A-9431-4E37-BFA1-3A7DF502191E.jpg

[Jimmy Harris]

That's an interesting idea. But it seems like it'll eat your stone faster that way. And, if you're going to buy some aluminum oxide powder to cut with, why not use it on a piece of plate glass?

I'm not trying to poo-poo your idea here. I just don't understand what the benefit is. I haven't tried it, so I don't know.

[John C Cox]

The "Benefit" is that I already own the India and Arkansas stones, and a set of water stones to replace them would be ~$250 vs the $60 I spent on loose abrasive.

Sure, it may wear the stones slightly faster, but Arkansas stones wear incredibly slowly as is. So far, I haven't seen any wear on mine, which is sort of a shame, as it would be nice to have an excuse to replace two of the three Arks in the picture. They are low quality and don't really work well by themselves.

This isn't an "Idea". I have been using this and it works really well.

[Rafael Herrera]

I haven't tried to use the grits you have, only coarse SiC grits on float glass to refurbish oil and water stones.

I tried using SiC on float glass to lap the back of chisels and irons. I didn't work, it was more effective to use PSA sandpaper. I haven't tried finer SiC grits on glass with steel.

I've tried diamond lapidary powder on a hard Arkansas stone out of curiosity. I didn't notice a huge difference compared to what I normally get. The diamond powder is really fine, so a dramatic change wasn't expected.

I don't really go beyond light passes on the Washita/Soft Arkansas before the strop, my medium India does most of the grinding when needed. I rarely use the hard black or the translucent Arkansas. They polish , but so does the strop with compound.

I've not tried Aluminum oxide, it'll be interesting to give it a go.

[John C Cox]

I lap the backs to P1000 PSA sandpaper on my surface plate. I don't touch them again until either 1-3 micron or 0.5 micron alumina on the soft Ark. It works beautifully to wipe off the burr, but doesn't mess up the geometry.

I'll take some comparative pix at each sharpening grit for reference. It's sort of nice to see each step and what it gives.

If you're going to buy abrasive, get it from an actual Lapidary supply. Amazon stuff is poorly graded and is more for beginners with rock tumblers. The only upside is that the Amazon stuff comes in nifty little jars where the good stuff comes in baggies closed with bread twisty-ties.

The reason I wanted a finer finish was for my paring chisels. Honing to a finer finish then only takes a tiny bit of buffing to get it to hold up to moderate paring. Stuff for malleting does just fine when I run it up to P800 sandpaper on the worksharp and then buff aggressively. You can really mallet with that edge and it will go and go and go, but it's not the best for paring soft wood.

[Warren Mickley]

I have used a soft Arkansas stone on every tool I have sharpened for over forty years. I never abrade it. I have recommended the soft Arkansas for people who abrade their hard Arkansas stones to make them "cut" faster.

I think what you are doing is a great waste of time. It sounds like you are abrading the soft Arkansas stone to make it more like a fine India stone, because you abraded your fine India to make it more like a medium India or whatever.

The soft Arkansas is a polishing stone not a "cutting stone". We use it to remove scratches from previous stones, not so much to remove material. We have used natural oil stones this way for millennia.

[John C Cox]

If you want to give this a roll and you don't have lapidary graded alumina... Shake some Shapton fine stone lapping compound on a soft Ark and give it a whirl. Oil works great. Water seems to cut faster, but it produces a very even, dull mat finish with this compound. It behaves like it has some sort of cleaner mixed in, which slightly etches the steel. Marketing ad copy says ~4000 grit (JIS.). I had some from a project years ago and it works quick but leaves a finish like you'd expect from that grit level. Don't like it? Scrub it off with soap and hot water, and off you go.

I suppose if you were really curious, you could scrape a blob of mud off a fine grit water stone and smear it on a soft Ark and give it a whirl. I bet you would be surprised by how nice it works. I certainly was.

Interestingly, assuming soft Arks that don't throw sand, they behave more like a substrate than the stone they once were. Each alumina grit produces an incrementally finer finish that tracks the abrasive more than the soft Ark. So, for example, the 1-3 micron polish leaves a much finer finish than I ever got with the soft Ark alone.

Unfortunately, my phone doesn't take the sort of pictures which are useful for showing the differences in finish, but they are significant. I personally doubted that 1-3 micron alumina would do anything useful on a soft Ark, but it really does. I don't own any water stones, but the finish it leaves is finer than a DMT ultra fine (3-micron).

Going through the grits is quick as well. None of them took more than 2-dozen strokes on a 20-degree full flat bevel. Teasing off the wire edge is fast and painless on the fine polish treated ark. That surprised me, as with untreated stones, I could get there, but it was ssslllooooowwww.

[Charles Edward]

Garrett Hack, diamond paste-on-stone:

https://www.finewoodworking.com/proj...-hone-a-chisel

Garrett Hack portfolio:

https://www.garretthack.com/

Seems to have mastered sharpening woodworking tools.

[John C Cox]

I had not seen that before, but there is nothing new in the world. So he uses diamond paste on a fine India stone, with the explanation that his fine India is glazed... Sounds familiar. A pound of 500 grit Silicon Carbide costs less than a 5-gram tube of diamond paste.

I bet he would love a decent soft Ark charged with diamond in the 1-2 micron range.

[Charles Edward]

I had not seen that before, but there is nothing new in the world. So he uses diamond paste on a fine India stone, with the explanation that his fine India is glazed... Sounds familiar. A pound of 500 grit Silicon Carbide costs less than a 5-gram tube of diamond paste.

I bet he would love a decent soft Ark charged with diamond in the 1-2 micron range.

I suspect he's happy with his routine and what it does for him in the shop.