Thread: flattening honing stones.

As a follow on from the recent thread on sharpening stone boxes, I am including a quick run down on the process I use to flatten the top surface of my honing stones. The use of loose sic powder is generally restricted to those harder stones that are well out of flat when purchased 2nd hand on ebay, and would respond too slowly if worked on w & d sandpaper alone. After the initial flattening of the stone with the loose sic process, general maintenance of the top surface of the stone shouldn't require much more than a light work over using 400 grit w & d. Extra care should be taken when working narrower type blades and chisels across the surface of stone to avoid localize wear.

The following is a purple welsh slate stone that has a lime green inclusion to one end. The loose sic powder being used is 280 grit. To avoid localized wear over the float glass, its recommended you work the wet sic slurry and stone in a figure 8 motion, utilizing the full flat surface of the float glass. Randomly reversing the direction of the figure 8 motion is also considered sound practice.



At the completion of using the loose sic powder, its recommended you leave the wet slurry to harden to a dry crust before clean up.

Before moving onto the final stage of refining the flat surface of the stone with 400 grit w & d adhered to a piece of float glass, its recommended you clean the stone thoroughly in a container of water to remove any grit contamination. Dry the top surface of the stone, then mark its surface with a lead pencil. If you closely at the following photo you can see a small darker area on the stone's surface that is obviously still low.



A quick work out using a circular motion across the 400 grit w & d has been able to remove all of the pencil markings, indicating the top surface of the stone is now totally flat.

As mentioned in the opening post, its recommended you allow the wet sic slurry to harden to a dry crust. From that stage, its a simple matter of using a paint scraper to work the crust into a center pile that can then be troweled into the scrap bin.



A quick wipe over with a damp rag and the float glass is ready for the next time its required.



Hopefully the forum members gained some value from this thread.

StewieS;

Something I have always been curious about is if you can use something such as aluminum oxide to get even finer grits for lapping.

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Yup, you can get a progression of 60 grit to 500 grit for about $15 from Gotgrit.com.

60 grit will get to flat in 15-20 mins, but a soft stone like a slate, will get flat on 120 grit drywall screen and water on a steel cookie sheet.

A steel cookie sheet will stay flat and contain the mess, $1 at the Dollar store. Lay on the floor and use your bodyweight for hard stones.

I was thinking about some 1200 aluminum oxide for finishing thuringians and to improve on my massive zulu. Do you think it would work?

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The notion that going to 60 grit sic will quicken the process is a slightly floored argument from my experience. To make matter worse, it feels like your rubbing your stone across a moving layer of oversize ball bearings. The larger the particle size your starting with, the quicker that breakdown takes place. Mixed with water as a lubricant, your trying to create a fluid grinding paste, that's not overly coarse in nature. Personally, I have found the best results occur between a range of 150 to 280 sizing.

Adding more lubricant with a spray bottle as you can feel the slurry starting to dry off and slow the movement of the stone is a critical learning point to this process, as is knowing when to add some additional sic powder to the slurry mix when the particle size has broken down to a size that is no longer serviceable. The amount of sic powder needed is not high end, with little more than a 1/3rd of a flat teaspoon, to start with, and a 1/4 flat teaspoon once, maybe twice to complete the flattening process.

The most difficult type of honing stone I have encountered using this process, is not a natural stone, but a man made Norton Carborundum/Crystolon Fine Grade Stone. Trying to flatten 1 of these that's heavily concaved from previous misuse, can be a real test of anyones endurance level.

As to Aarons question on using loose grit 1200 Alox powder; I am not sure why you would bother, when a better option would be in W & D sheet form. In my case, I see no benefits in going any higher than 400 grit in sheet form. But don't let any of my comments stand in the way of further experimentation.

regards StewieS;

I should include a caveat with any of my posts on this forum. I only work with wood. The closest I get to a sharpness test with any of my body hair is on my forearms. I prefer to hone the cutting edge on my tools to 1200 grit, then add few swipes on a leather stropping block with pure oxide paste. I have no idea how to compare my level of sharpness to what you guys can achieve with a flat razor.

StewieS.

Why not use a progression of sandpaper on a kitchen worktop?

My reason is because I have a stone that is over 11in. they don't make sheets of high grit sandpaper large enough to lap this particular Stone properly.

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