Should you flatten a Carbonized Silicon sharpening stone?

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johnbfjfds

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Nov 30, 2015
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I bought two 12" x 2.5" * 1.5 " carbonized silicon combination sharpening stones since they were the only 12" stones I could find. They were super cheep at around $5-6 each plus about $10 shipping. These stones are big versions of the typical kind found in everyone's kitchen, usually as a combination stone with one dark gray rough side and a lighter gray or white finish side.

They are not water stones, meaning they don't easily loose their top layer of abrasive material. They are made by using super high heat to fuse together sand into a porous solid.

The challenge to the stones were that they are not not at all flat. In addition to a dished center they also have a few irregularities, all of which would adversely affect sharpening. To make the stone flat I bought big sheets of sandpaper at Home Depot used on floor machines costing around $6 a sheet. About 4 sheets were necessary for one stone. Two 60 grit, one 80 grit and one 100 grit, total cost $25. The stone is now flat but is also much smoother than it was before. It doesn't bite the blade much.

Is there a way to flatten a carbonized silicon stone without making it so smooth that it is no longer effective at sharping?
 
after its flat, you "condition" the stone so it cuts again, this just mean clean/wash/scrub it, then rough it up so its cutting again, 5-10 second light scrub on sandpaper ... or rub it with a piece of hacksaw to raise some slurry so it cuts like new

smoothing is inevitable, either from sharpening or from flattening

also, don't spend too much money on sandpaper for flattening, all you need is flat piece of glass or a ceramic tile or concrete paper, a pinch of sand and some elbow grease :)
 
This ^

Use a pinch of sand, or as the sheet you are using to flatten them becomes worn, leave the grit it sheds to accumulate. Make sure to use water, oil, something as a fluid for the loose grit to knock around in. Using a hard fixed abrasive will leave the abrasive glazed, that's what has happened.

As above, you can flood it with oil and rub vigorously with a piece of steel - old saw blade, old file, spine of knife you don't much care for etc. This will recondition the surface, but it will happen a lot faster if you use a loose abrasive grit on a hard surface. I've heard of people using a flat stretch of sidewalk and a lot of water. I use silicon carbide grit on an Arkansas stone or another flat combination stone.
 
After flattening any type of stone I take it over to the "dirty" side of the shop and go over the surface with compressed air to blow all of the swarf out of the crevices. Rinse and repeat. It really helps them to cut.
 
With all of the money spent on shipping and sandpaper, and all of the time spent trying to flatten these stones, which don't even seem to make an appropriate cutting surface, one has to wonder why you'd bother. A Norton Crystolon stone would seem to be a better compromise of time, money, and quality.

Brian.
 
I would stop by a harbor freight or some where that sells sand blasting media. Double digit grit if you can, but basically anything coarser than the stone itself. Using loose abrasive to lap the stone will keep the surface from polishing. These stone have such a strong binder that the abrasive in the stone wears smooth before being pulled out. Also, harder wearing stones like that benefit from using higher pressure to sharpen. It helps break up the abrasive while sharpening.
 
fervens said:
I would stop by a harbor freight or some where that sells sand blasting media. Double digit grit if you can, but basically anything coarser than the stone itself. Using loose abrasive to lap the stone will keep the surface from polishing. These stone have such a strong binder that the abrasive in the stone wears smooth before being pulled out. Also, harder wearing stones like that benefit from using higher pressure to sharpen. It helps break up the abrasive while sharpening.
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I've looked at homedepot and harborfreight , they don't seem to sell blast media by the pound ... spending $25-50 on a 50lb bag of blast media seems silly :) for that price you can buy a circular saw diamond tile blade, (or if right sale both saw and blade) which you can use to flatten any stone
 
It really does work best with a loose grit. One can order 60 or 80 grit SiC by the pound from lapidary supply shops for a few bucks and that pound will last a long time. Using any hard fixed abrasive like diamond will glaze the stone as it flattens/cuts it, needing some conditioning after. Not a big deal with a silicon carbide stone, but a lot tougher on something like an India.
 
Yes, an India is very slow going. I did one of mine on a flat area of concrete and used SiC grit. It was slow going even using 100 grit. The binders are really strong on this type of stone. But once you do it they will last a long time. Not the same for the SiC coarse. It responds to leveling much better. And I've had to do this stone twice in the last 8 years. It takes about an hour for the SiC or an Arkansas stone. The India and ceramic take hours of rubbing and the treatment will last double what the SiC stones last. DM
 
fervens said:
These stone have such a strong binder that the abrasive in the stone wears smooth before being pulled out. Also, harder wearing stones like that benefit from using higher pressure to sharpen. It helps break up the abrasive while sharpening.
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Agreed. DM
 
A great amount of good information
This is what makes being here a great place

Thanks!
 
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