Renovate natural sharpening stones?

[DigitalM]

I saw a few nice old sharpening stones today at a car boot. I didn't buy them as they looked a little worn, not much, but you could see it by eye. One looked something like slate, another, after some googling, may have been a "dalmore blue".

Anyway, as I car boot a lot, I was wondering if there's an inexpensive way to flatten and renovate these? I don't mind putting a few hours of hard work in, if it can be achieved in that sort of time frame.

I tried googling this and it returned many videos about flattening water stones, but they look way softer so those techniques may not apply. Also, the guy rubbing his Arkensas on the concrete in the back yard - well, I suppose that's fine but suspect someone may have come up with a smarter way.

I was wondering, silicone carbide paper on a marble slab?

I'm suspecting the answer will be "Yeah, you can do it like that, but it will take 6 weeks and by the end you'll have arms like Popeye!".

Any tips appreciated.

 

[Jacob]

You don't need to flatten them just sharpen in the old fashioned way like the previous owner. It's the smart way - quicker and easier.
All this stone flattening is just a time wasting crack-pot modern amateur woodwork fashion. Nobody ever did it in the past (except for special purposes) which is why nearly all old stones are hollow. They knew what they were doing.
May need freshening up. I use 3m diapad for this as it's bendy and will follow the curve of the stone, plus oil, or white spirit if very clogged up. Just a quick rub over. A stainless steel pan scrubber is good too.
Should take just a few minutes to get them into use.

 

[bugbear]

The natural novaculite stones (Arkansas, washita, Charnley Forest) are very hard to flatten.

Synthetic Norton India Stones are very hard to flatten.

Most other UK stones can be flattened fairly easily using water and a sheet abrasive (around 60-80 grit) on a flat surface.

BugBear

 

[ED65]

Re. flattening, there's written reference to using the right kind of sand to flatten stones from before Carborundum was available, which makes it from before even Jacob was born. So do take his "All this stone flattening is just a time wasting crack-pot modern amateur woodwork fashion" thing with the appropriate pinch of salt 8)

Anyway regardless of what was or wasn't done historically if you want a stone flat make it flat, it's your stone and nobody else's opinion has to matter.

Anyway, as I car boot a lot, I was wondering if there's an inexpensive way to flatten and renovate these? I don't mind putting a few hours of hard work in, if it can be achieved in that sort of time frame.

It should be possible to do it in under a few hours with most stones. How long it takes obviously depends on how hard the particular stone is, and some are hard as hell, plus just how dished the surface is needless to say. I've only done it a few times but the longest it has taken me is very approximately an hour and a half, all in.

Yes you can flatten many stones on a concrete block, or even on a suitable bit of pavement in front of your house. Doing it on concrete is much slower than on abrasive paper or loose carborundum powder but it is doable, even for some of the tougher stones. You'll wish you had arms like Popeye when you're done if the stone is any of the harder varieties, I guarantee it!

If a stone doesn't need it and you just want to clean it well first call can be literally to scrub in hot, soapy water. Long soaks in solvents such as gasoline or kerosene are also widely used and can be amazingly effective at returning a grotty old thing to its (often surprisingly pale) original colour.

 

[DigitalM]

Well, without wanting to start one of those debates, one of the reasons for wanting to lap the stones, was (no laughing at the back) some of them are quite beautiful, and I suspect lapping them might really bring that out. I like tools, and I like patina, but I also really enjoy rescuing knackered old stuff!

 

[D_W]

If they are swayed significantly, the hard drum on an inexpensive belt sander (stationary type) can easily remove stone at the contact point. This is an outside-only exercise and with respiratory protection. Once you've spot removed a stone to mostly flat, then you can take it to a hand lap.

Sedimentary stones (slates, etc) can be done on almost anything (wet/dry or just plain aluminum oxide sandpaper). I still find coarse diamonds to be fastest for final work on novaculite stones, but I haven't tried some of the messier methods.

As for the belt sander, an inexpensive 80 grit al-ox belt (cheap red type) is perfectly fine. It's far harder than the abrasive in natural stones.

(laying the stones flat on the platen of a belt sander gets you nowhere fast if you have to remove a lot of material, and it strains the belt sander).

 

[Jacob]

Re. flattening, there's written reference to using the right kind of sand to flatten stones from before Carborundum was available, which makes it from before even Jacob was born. So do take his "All this stone flattening is just a time wasting crack-pot modern amateur woodwork fashion" thing with the appropriate pinch of salt 8) ....

You can find all sorts of bad advice even in old books!
But we know it wasn't widely done (nearly all old stones you find will be hollow) and we know it isn't necessary; anybody sharpening freehand will not need to flatten stones - it's only for jig users.

I'd just clean them up with diapad or pan scrubber. 10 minutes max and they will be usable. No need to be a fashion victim - be smart and stay ahead of the game!

 

[Cheshirechappie]

Many trades use edge tools, and need to keep them sharp. Not all trades have edge tools with a flat jigging surface, such as a wood chisel has, so not every trade needs to 'back off' on a flat surface. For example, butchers' knives have double bevels, neither of which needs to be flat. Consequently, the sharpening stones used by butchers don't need to stay flat. For example, here's Scott Rea showing how to stone and steel butcher's knives - https://www.youtube.com/watch?v=Okv6N7KfR6A

Since woodworkers use edge tools with flat jigging faces, sharpening stones maintain their tools in best condition when they are flat, and all the old reference books suggest this as best practice. Other practices are possible, just not 'best'. (Not every woodworker was a Chippendale; in any walk of life one can find those who, given the tools, will finish the job; and those who, given a job, will finish the tools.)

 

[--Tom--]

Disk sander with a coarse disk will get you nearly there before you lose the will

 

[Racers]

7 to 1 at the moment, I would flatten as well so 8 to 1.

Pete

 

[AndyT]

I wouldn't bother flattening.
White spirit and an old toothbrush will lift off any old dried oil.

 

[G S Haydon]

Difficult to advise. Clean it and give it a go. If you can raise a burr and remove one then it's good. If it's not able to do that I would and have done what DW mentions. Did it with a Charnley and took no time. Flattening anything is a bore and best avoided when possible.

 

[Jacob]

.....
Since woodworkers use edge tools with flat jigging faces, sharpening stones maintain their tools in best condition when they are flat, and all the old reference books suggest this as best practice. ....

You get occasional references to cleaning up stones on slabs with 'sharp sand' but it's virtually a 'meme' - endlessly repeated and ignored.
"Flat jigging face/surface" is not woodwork terminology and you won't find it in any of the older books. Jigs didn't come in big time until the 1980s and later, with the burgeoning amateur woodwork supply industry.
I've sharpened all my tools on un flat stones for 50 years or more. though I did flatten one once to see what it was about. Waste of time.
Old stones are almost always worn hollow with use. Old chisels are always slightly convex along the face with years of sharpening. Old plane blades are flattish on the face only for the first few mm in order to locate cap iron.
They did know what they were doing, believe it or not.
Carving chisels are sharpened more than most blades and they have rounded bevels, sometimes on both sides. etc etc etc
"Best practice" is another pseudo technical term which people bandy about aimlessly!

 

[Jacob]

I wouldn't bother flattening.
White spirit and an old toothbrush will lift off any old dried oil.

Yes, though sometimes I go the extra half inch by freshening up with a diapad or pan scrubber - surfaces can get clogged up.

 

[essexalan]

Flatten them. Scrape as much of the crud off then hit them with 80 mesh SiC grit on a flat granite offcut, drop of washing up liquid and a splash of water. Make sure you use all the surface of the granite to keep it nearly flat. Expect a horrible noise until the SiC breaks into smaller particles when you add more SiC. Arks and Washita take the longest depending how much they have been abused, slates take minutes. Some naturals you can flatten quite quickly on abrasive belt as DW mentioned but not Ark/Washitas. I would not let my diamond plates anywhere near a natural stone except to bevel the edges and even then I usually use SiC paper which you can use to dress the surface of the stone after flattening.
My carving chisels start off with flat bevels but the constant stropping rounds them off so back to the stones, read a Chris Pye book who does know about carving.

 

[bugbear]

Jigs didn't come in big time until the 1980s and later, with the burgeoning amateur woodwork supply industry.

Flat out plain and simple wrong. Evidence available.

BugBear

 

[Seiken]

I've flattened oilstones on a paving slab, I've still got my school woodwork class notebook from 1969 and there it is as copied from the blackboard in the classroom.

 

[D_W]

Re. flattening, there's written reference to using the right kind of sand to flatten stones from before Carborundum was available, which makes it from before even Jacob was born. So do take his "All this stone flattening is just a time wasting crack-pot modern amateur woodwork fashion" thing with the appropriate pinch of salt 8) ....

You can find all sorts of bad advice even in old books!
But we know it wasn't widely done (nearly all old stones you find will be hollow) and we know it isn't necessary; anybody sharpening freehand will not need to flatten stones - it's only for jig users.

I'd just clean them up with diapad or pan scrubber. 10 minutes max and they will be usable. No need to be a fashion victim - be smart and stay ahead of the game!

10 minutes is about how long it takes me to take a quarter inch of sway out of a novaculite stone and lap it.

It's not always necessary to lap a stone, but it doesn't hurt anything, either. Without a hard contact point on a belt sander, this is otherwise extremely slow work.

 

[D_W]

I guess I should correct that to say that the contact point is a line. There will be a line of fire where the contact occurs on a novaculite grind, too. And it'll small like fire.

 

[Jacob]

Jigs didn't come in big time until the 1980s and later, with the burgeoning amateur woodwork supply industry.

Flat out plain and simple wrong. Evidence available.

BugBear

What evidence? In fact they were around but hardly anybody used them. We learned trad sharpening at school and again later when I did a course. Gadgets were for the amateurs and beginners. You'd be laughed out of the training workshop if you got out a little jig!