Lapping advice for Translucent Arkansas?

[bernie01]

My first Ark arrived, pictured doing it's translucent thing. It's a "Chris Pye Signature" model with Norton Pike on the case. The side pictured is very close to flat but not perfect, I thought to do a bit of work with Wet&Dry paper? I have 120, 240, 400 and 600 grit. Would this be suitable? What grit(s)? Any advice appreciated, thanks. I have a sink cut out from a granite counter top as a smooth/flat surface to lap on.
<Edit> I have been referred to this, thanks! Lapping Hard Arkansas - https://www.badgerandblade.com/forum/wiki/Lapping_Hard_Arkansas

 

[Mr. Shavington]

The Ark should make your wet & dry paper nice and smooth in no time.

 

[lightfoot]

First inspect the stone with a certified straight edge. If it’s already flat you could proceed with silicon carbide (black) sandpaper in the grit selections you’ve mentioned but I actually like to bring translucent stones up to 1,000 but that’s just me.

 

[Herrenberg]

Sprinkle your sandpaper with silicon carbide powder in a comparable grit, and it will function for a lot longer, assuming the backing is decent.

 

[bernie01]

The stone is slightly elevated at each end; you can see from the photo where the previous owner (who sharpened chisels etc on it) has not really used the full length of the stone (which is 8"). So it needs a bit of work to be flat all over. The Wiki page I listed above is very informative; looks like I'll be buying SiC powder and Wet&Dry sandpaper soon! Thanks to all for the input.

 

[Wid]

I use sic powder up to 600 grit then 600 wet/dry sandpaper. That’s it for me. Then I take a knife to it before a razor. Any higher and it wants to burnish. I don’t care much for it to be burnished. When it does I take it back to 600.

 

[H Brad Boonshaft]

Yup, follow the instruction on that WIKI link. Stay on 60 grit until the stone is flat, (you can remove a sharpie grid in less than 10 laps). A pencil grid will wash off with the loose 60 grit and slurry in a few laps and you are no-where close to flat.

Wet and Dry paper will not cut enough to flatten an Ark, well, perhaps but you will need packs of 60 grit paper and lots of time. For $15 you can buy all the grits of loose Silicone Carbide from 60-600, from Got Grit.com, enough grit to do a couple stones. You will use way more 60 grit that the others. As said from 600 loose go to Wet & Dry. 600 Wet & Dry will polish a bit higher than loose 600.

Once the stone is flat, it is much easier to refine the stone face with wet and dry.

You can also add 60 grit diamond to your 60 grit Silicone Carbide to speed up the cutting power.

A steel cookie sheet on your granite counter or a granite floor tile on a piece of flat cement floor will work. The steel cookie sheet will remain flat and contain the mess. Granite is softer than an Ark, honing on the Granite with 60 grit Silicone Carbide will dish the Granite.

If I was lapping stones with loose Silicone Carbide on our Kitchen counters, my bride might have something to say about that…

The good news is that you only need to lap it flat once.

BTW, the Grey translucent with black streaks, glued to the wood block, middle, bottom row in the post photo is mine, great stone.

 

[bernie01]

Granite is softer than an Ark, honing on the Granite with 60 grit Silicone Carbide will dish the Granite.

If I was lapping stones with loose Silicone Carbide on our Kitchen counters, my bride might have something to say about that…

If I use W&D on top of the Granite, and SiC on top of the W&D I think it will be OK. It's not the actual kitchen counter, but a piece cut FROM a kitchen counter where the sink goes.
<Edit> Come to think of it, the piece of kitchen top I have may be marble. I got it from a mate, will have to check with him. It's black, with sparkles in it. Is marble harder than granite/Novaculite? </>

 

[Legion]

Is marble harder than granite/Novaculite? </>

No. Marble is quite a bit softer.

 

[duke762]

I'd just like to mention, I hate checking trans Arks for flatness. My tired old eyes and the light being transferred through the stone instead of under the straight edge.....I think they end up getting my best guess and not my best work.

If you have a really deep dish, that is going to be hard to lap with conventional SIC, do not be afraid to use silica sand on concrete or steel or even a fairly flat granite tile from Lowes or Home Depot. Do the heavy lifting ( if needed ) with the cheapest, most aggressive thing you can find. Get it closer to where it needs to be and then use SIC grit followed by fixed 600 grit paper for final dressing. Actually, I have persisted on the lap with broken down silica sand and polished the Ark to levels I wouldn't use it at. Check your work frequently with the straight edge.

 

[bernie01]

If you have a really deep dish

Actually it is only minimally dished; more worn uniformly in the middle 6" but not worn on the 1" at each end. I can barely see daylight under the straight edge but would like to get it lapped then I don't have to worry about it for a long time. I think it will flatten pretty quickly and nicely once I've knocked those ends down. I've ordered SiC powder and W&D in 60/120/240/400 and 600 grit.

 

[H Brad Boonshaft]

What you want is that the Ark surface is smooth and there are no pockets that are not smooth and will surface as the stone wears, (a new, never lapped or used stone). Arks do not need to be Dead Flat and a Translucent is not going to be removing steel so that it will conform to the shape of the stone, it will only polish.

The whole lapping stones Dead Flat is a new thing, vintage stones were never lapped “flat”.

I only buy vintage Arks. You might try it before you touch any abrasive to it. A well-used stone is a burnished smooth stone and may just need a good cleaning to be a stellar performer.

Spray with Oven cleaner and scrub, followed with an over-night or two soaking in Simple Green or Dawn Degreaser and a good scrubbing.

Try honing a knife on it, if the surface is smooth try finishing a razor after a good 8k or equivalent edge on it.

You may find the stone is perfectly burnished, you have nothing to lose.

I lap on a 18X24 inch piece of granite countertop, laid on the cement floor under a dollar store steel cookie sheet.

On the floor you want to use your body weight on the stone, add a ½ teaspoon of grit when you feel it stop cutting, rinse the slurry on to your grass not down the sink.

Try the stone first, it may take you years to get it back to the finish it has now and “flattening” it may only take you backwards.

 

[Darth Scandalous]

What does the other side look like? If it's largely flat but uneven, it will probably be easier to lap down than the dished side.

 

[bernie01]

Well, I've ordered the SiC and W&D so will lap it when they arrive even though there is negligible wear (that cost me more than the Ark). Will have a play with it in the meantime, thanks for the info. May well lap both sides if the first side doesn't wear me out, and finish to different grit levels on each.

 

[Eshebert]

I don't keep a bunch of Sic on hand. I get a $7 rock tumbling sic kit on amazon when needed. Its enough to lap a half dozen stones or 2 or 3 Hard Arks. Then I finish with 600 WD, no real reason for 600 other than that's about the coarsest I keep around the shop. I been using ceramic tile as my base, but that wont last but about 2 stones worth of lapping. I also have a Translucent Ark coming, I'm switching to stainless steel for my lapping base. I have some sitting around, not sure why I didn't think of it earlier.

I will tell you what else works well. I have a pile of 180 belt sander belts from and old sander I no longer have. I cut them in 10-12" strips and lap the heck out of them, you can add your coarse sic on top of that.

 

[psfred]

All Arks are very hard (due to being basically pure partially fused silicon dioxide), so lapping is gonna be slow.

I would try it before you lap it, as noted you are just polishing with light pressure and unless the edges are really rough or the dish is deep enough to damage the edge, you might be happy with the surface as is.

It will take a long time to smooth it back out from 60 grit SiC lapping -- I have a huge washita I'm grinding on right now to get the large but shallow dishing out of it.

 

[Gamma]

We don't drive Model T cars, wait a month for newspapers, or go to school in a one room shack anymore.
Things change. We call it progress.
Lapping things flat isn't new though.
We say dead-flat so everyone understands the intention of removing variables from the picture.

We lap stones flat because, well, flat is flat and when the stone is flat that is one variable out of the picture.
Flat is dead flat. Not flat is not flat. If you lap something flat, it's dead flat.
If you don't lap it dead flat - it's not flat. Simple.

If the edge is going on my face, I want the finisher dead flat. A flat finisher, used correctly, is easier to achieve a true apex on, which is inevitably smoother than what an uneven surface might make.
There is wiggle room in there, maybe, possibly, sure, but there is no point in taking half steps when I can just do it right and know for sure it's 100%?.

Anyway - what @Wid said - SIC up to 600 and w/d 600x. It works.
Polishing a finishing Ark to mirror gloss has proven to be counterproductive to me.

If the stone is starting out rough, I start on 60x SIC on a true flat substrate using w/d paper as a sacrificial surface.
I've removed plenty of deep dishes out of very hard Arks, it works. I'm talking dozens of stones, not 3. I don't like to use coarser grit than 60x because then I have to remove the inevitable striations mess with a lot of extra work. TBH I don't like using 60x all that much for that reason. If the surface is only a little out, I will usually start on 80x SIC.

 

[bernie01]

I found out that the piece of kitchen counter top I have is actually granite, which is good. I'll use SiC powder on top of sacrificial W&D sheets on the granite and monitor the (polished) granite surface for any wear. If it does start to wear I'll have to source a cookie tray.

We lap stones flat because, well, flat is flat and when the stone is flat that is one variable out of the picture.

I need as many variables removed from my honing as possible so I'm aiming for 'flat'.

 

[Mr Kooby Shemayrew]

I found out that the piece of kitchen counter top I have is actually granite, which is good. I'll use SiC powder on top of sacrificial W&D sheets on the granite and monitor the (polished) granite surface for any wear. If it does start to wear I'll have to source a cookie tray.


I need as many variables removed from my honing as possible so I'm aiming for 'flat'.

Don’t do it. It will wear. I use a big block of granite with SiC to lap stones. I got this from a hardware store and it isn’t expensive. You don’t want to scuff up, or worse, dish out a polished counter top.

Lapping hard Arks isn’t rocket surgery. It is more effort than science. A lot of effort. We’ve all suffered. Now it’s your turn.

 

[H Brad Boonshaft]

Do yourself a favor buy a steel cookie sheet from the Dollar store, it will keep the surface flat and contain the mess.

Lapping is a lot of work, if you lap/grind on a substrate that will dish, you will grind the stone convex.

Spend a Dollar, or do it all over again.

Guys that lap and certify precision lapping plates, claim that lapping on wet and dry on a precision lapping plate will concave the precision lapping plate from the swarf and dust/grit that gets between the back of the paper and the granite plate.

Imagine what grinding on a granite or marble tile with 60 grit will do.