Flattening an Oil Stone...

[Barney Rubble]

Hi All,

Was hoping you might be able to offer some advice on how I can flatten an old India stone. It was given to me a while back as it used to belong to my wife's late Grandfather. It's a lovely fine stone but I noticed (when I pass my knives over it) that it has developed a slight concave surface where I suspect it's been used to sharpen chisels and the like.

I wondered if there's anything I can do to flatten it so that I can use it to sharpen my knives?

Any advice is gratefully received.

 

[bopdude]

Loads of Youtube videos, too many to list

 

[brancho]

Basically fix some abrasive paper to a flat surface lubricate it with what you use on the stione and sand it flat using a circular motion

https://www.youtube.com/watch?v=uWp_GxQkRgw

 

[MartiniDave]

Or ignore it. A bit of convexing won't do a lot of harm, some even say it improves the blade performance.

 

[C_Claycomb]

From the description, it sounds like the concavity is in a strip down the middle, like a canoe, rather than across the middle, like a banana. Banana concavity isn't too much trouble if the blades being sharpened are convex or small secondary bevel, but it is a bit of an annoyance if they are single Scandi grinds that you want to keep flat. If you don't keep them flat, you are then forced to match the slight convex grind with all subsequent sharpening grits. I love convex, but when I want flat, I want flat!

Flattening or lapping oil stones is the same process as flattening water stones, just different lubricant, and the oil stone might take longer since they generally wear down slower. I would go for a coarse grit, something like 120. For a flat surface, lots of things will do, but I have used 12mm thick glass for flattening. The main things are that the surface be flat and that the material not absorb or react to the fluid you are using to lubricate the process.

Good luck. It can take a while but is worth it.

 

[Woodcutter2]

Hi, I had and have from time to time the same problem with my favourite Carborundum stone and an ancient slate polisher used most weeks to keep site chisels and plane irons shaving sharp needing periodic attention, for speed and price a tip from a bloke on site was cheap diamond stones (diamond ,ish, impregnated metal strip bonded to 5mm thick plastic) from Aldi and been seen in Lidl for about £8.99 in three grits, then glued with epoxy to a slab of soft/hardwood or some such flat stuff and worked with WD40 is a fast and accurate enough method to bring them back to a very acceptable level of flatness.

I use a worn out (on A2 and CPM3v) DMT continuous diamond stone to care for my Shapton Glass stones, works a treat. hope it helps.