Est. 1998 — 27 years of woodworking knowledge
Question for the gang.
Bill White
I inherited a Smith's Soft Arkansas stone recently. It is convex on both sides. Not radically.
Was wondering how best to flatten both without wearing myself and the stone completely out.
Concave is not a prob for me. but the convex (rocking on a flat surface) has me flummoxed.
Any thoughts.
Re: Question for the gang.
David Weaver
you can lap it on plastic sheet or glass with loose silicon carbide grit, or you can (if you have an inexpensive belt sander with a short radius idler on one side) run it criss cross on the idler of a belt sander and knock most of it off and then finish lapping what's left into uniformity with grit or a diamond hone.
Taking a whole bunch off with just a diamond hone is a good way to make the diamond hone really tired, though (and it requires a very expensive coarse diamond hone).
Cheap aluminum oxide belt on the idler of a belt sander (is on, just a thin line of contact) removes material from an oilstone quickly (mask is obligatory - smells like burning bone).
Re: Question for the gang.
Oskar
What about abrading a small concave in the middle, with a angle grinder/belt grinder/loose SiC on something round. This way you could get a concave part started, which give you two contact points when lapping normally afterwards?
Re: Question for the gang.
Warren in Lancaster, PA
If the stone is convex in the lengthwise direction, it is not a problem at all, and normal wear will even it out somewhat. (Because we usually don't sharpen to the very ends).
Having the stone convex across the width is more of a problem. In that case, if you sharpen a plane iron just back and forth, the iron might become a little hollow and then in use just cut at the edges. If you can learn to sharpen the iron focusing on the whole width by slowly adjusting it side to side as your strokes are back and forth, you can handle it.
Sharpening narrow chisels and carving tools, where you can't sharpen on the edges of the stone, will tend to concentrate wear on the middle of the stone and eventually even things out also.
Re: Question for the gang.
Steve Elliott
If you use sandpaper narrower than the length of the stone and move the stone across it so that the ends of the stone are never over the sandpaper you can remove the hump from the middle and produce a very slight concave surface. The final flat surface can then be made by turning the stone 90 degrees and removing the high spots from the ends.
Re: Question for the gang.
Mike In Los Angeles
I’m not an expert but I think I would put it in a drawer for when I needed a slip stone, and if I thought I would never need a slip stone I think I’d give it to someone who wants that.
Re: Question for the gang.
Curt Putnam
I like Mike in LA's suggestion. I have heard of using a cinder block for lapping.
Agree! First, make a hollow place.
Re: Question for the gang.
Bill White
Thanks guys. I'll keep you posted.
Re: Question for the gang.
Charlie
The other side is probably concave and much more easily flattened. Do that side, and save the convex side for a rainy day.
Re: Question for the gang.
Charlie
Nevermind... I see it's convex on both sides. Bummer.
Re: Question for the gang.
David Weaver
bill - if you'd like me to flatten it, I'll glady do so. You'd just have to pay shipping to send it to me and I'll pay the return. It'll be dead flat and won't take me more than a fraction of an hour and there's no real cost to me to do it (perhaps 25 cents of materials).
Re: Question for the gang.
Bill White
David, you're on. I'll let ya know when I post it.
There is certainly no rush on completion.
conclusion for this stone...
David Weaver
..both sides were kind of pillow shaped, as bill mentioned. As far as a stone used for 40 years, it would've been kind of minor, but for a new stone, it was severe. Maybe a couple of hundredths high.
It took about 15 or 20 minutes of grinding on the idler of a belt sander (one hand on the stone, another holding a vacuum hose - otherwise the dust would've been intolerable indoors - even with a mask, it stinks up the house with a strange bone/burning smell).
Affter getting close, the flattening is just completed with a 220 grit diamond hone (this stone has never seen oil, so I used water). Maybe 5 minutes per side of finish lapping.
Is it too much effort? I don't think so, but I get the sentiment that these are $20 stones and nobody should have to do it (I get belts for this sander for about $1.60 each - it's the sander that I use to do large area flattening on metal), maybe 2/3rds of a belt used on this, so ballpark $1 of materials.
Top side is really flat. Bottom side may be out of flat around 1 1/2 thousandths now when I checked it (I couldn't say why - if there wasn't already another side dead flat, I would've spent another minute or two on the second side, but sometimes your arms get tired).
Re: conclusion for this stone...
Bill White
What size belt do you use? Grit(s)?
Re: conclusion for this stone...
David Weaver
my flat sander is just a mid grade "bucktool" 4x36 sander.
The virtue of it is that it uses cheap belts (60 grit red al-ox), has a low radius idler, much better tension than the typical 4x36 bench top type, direct drive and about double the belt speed of the bench top types.
But I did this with several washitas with an old cheap home depot belt drive type bench top sander. I always buy cloth belts from amazon wherever they're cheapest. When they're used to make chisels, they don't last that long so cheaper belt material or low quality joint tape isn't an issue (the kind that becomes brittle with age) - the belts won't be around that long.