Flattening an oilstone

[Mike Jordan]

Steve asked many posts back about this and I’ve finally got round to offering an answer. I’m sure that there are numerous methods but the only one I’ve ever needed is very simple, a cup of yellow builders sand, water, and a piece of 6 mm plate glass.
The glass is used on a flat bench top with a little water and the sand used as an abrasive. The stone is moved in a figure of eight pattern until flat, adding sand as required.
The method works quite quickly with my Norton India medium stone, the photo shows the reduction from 25mm to 20 mm but this is the result of more than 60 years of returning the stone to flat.
As an apprentice I was gifted a very fine stone which was reputed to have been used as razor hone for a long period, it had a hollow on both faces about 6 mm deep. I was told it was an arcanasas stone. I still have it to this day and it’s very hard but good, the effort to get both faces flat was considerable but it has not required touching again.

 

[Cabinetman]

That’s good to know thanks, I’ve used car valve grinding paste in the past but I think I prefer the idea of sand.
Ian

 

[AJB Temple]

Depending on how big it is, an angle grinder will take the worst off and speed up proceedings. Then flatten properly when close to level.

 

[SamQ aka Ah! Q!]

Depending on how big it is, an angle grinder will take the worst off and speed up proceedings. Then flatten properly when close to level.

...seriously? As Mike J. is talking about 2.5mm ( per face).over 60 years, might your reply not be better in the limestone paving thread? An Irish bicycle is not known for its finesse.

 

[—Tom—]

...seriously? As Mike J. is talking about 2.5mm ( per face).over 60 years, might your reply not be better in the limestone paving thread? An Irish bicycle is not known for its finesse.

With a dished stone and a gentle touch can speed up proceedings well. A 4” is perhaps better suited than a 12” petrol version though

 

[Steve Maskery]

It all sounds scary, but thank you very much.

 

[Trevanion]

An Irish bicycle is not known for its finesse.

You can get quite precise with an angle grinder believe it or not, I've managed to do a lot over the years and attain an acceptable result simply with an angle grinder and a bit of patience. As Tom says, a gentle and most importantly consistent touch is absolutely key, I would expect with a reasonably hard stone like a Washita or Arkansas you could get it within 0.5mm of flat with a diamond wheel with careful grinding, rubbing the stone on a piece of steel repeatedly during grinding will show the high spots as dark spots and you simply grind them down until the surface is reasonably consistent before refining it by hand.

In regards to flattening an oilstone, I have used the crude "Faithfull" diamond plates in the past with success. There's also such a thing as a "Precision Oilstone" which is used by engineers on machine surfaces for knocking down high spots and maintaining a flat plane, the way they're produced is they take a regular India stone and mount it in a surface grinder with a diamond wheel and precision grind it flat, a bit overkill for woodworking but I wouldn't be surprised if some pedant claims it to be the only way to sharpen tools.

 

[SamQ aka Ah! Q!]

Yes Dan and Tom, I've managed quite a bit of finesse over the years with a 4" angle grinder, knocking down welds for example, with an abrasive-impregnated 'sponge' to 'flush' a panel for painting. And, I take the point, "gently does it" or "very little and often".
In responding to the original suggestion, I was trying to put the task in context. 2.5mm over half a century; I felt even a gentle 'kiss' with a softish abrasive would risk furrowing the stone, exacerbating things.
In the light of Dan's comment, re a hard stone, a 'touch and test' regime, with a diamond wheel, well, one never stops learning.

ATB, Sam

 

[AJB Temple]

Fully agree with Dan. As noted above I use an angle grinder for this myself. I get packs of blades for my 35 years old angle grinder on-line with a face pattern that does the cutting and apply hardly any pressure. Can't recall now if I got the idea from a knife maker or my dad. Also very handy for stone polishing if doing for example a chamfered edge.

 

[toolsntat]

Fully agree with Dan. As noted above I use an angle grinder for this myself. I get packs of blades for my 35 years old angle grinder on-line with a face pattern that does the cutting and apply hardly any pressure. Can't recall now if I got the idea from a knife maker or my dad. Also very handy for stone polishing if doing for example a chamfered edge.

Your mention of stone polishing reminded me I have this option available for the smaller varieties....
Cheers Andy

 

[Phil Pascoe]

P.59, The Village Carpenter.

 

[Cabinetman]

And no mention of 8000 gri................... don’t mention the war, I think I got away with it.

 

[AJB Temple]

I'm going to change my name to Jacob so I can comment at length.

 

[Phil Pascoe]

I bet you can't write a 100+ page rant.