3 Stone Flattening Method??

[duke762]

I've seen this mentioned and may have even sought out illustrations, but I haven't completely grasped the concept. Is it even a feasible concept? My basic understanding of it is, if you lap 3 similar stones against each other (loose grit maybe??), you will some how end up with flat stones. Do the stones need to be inspected and orientated according to which way they are out of spec, compared to the stone they would be lapping against?

It all makes it sound so simple and makes me think, if it takes 3 to get flat, and I happen to have, x number greater than 3, and of the same type, then success is guaranteed with excess precision? All I have to do is rub them together, randomly, with some kind of abrasive? Lord I wish it was that simple.

Using my usual, conventional methods, I wanted to test my flattening abilities, or perceived flattening abilities, I took a stone I had recently finished lapping (Black Ark)to work and set it up on the granite inspection plate. I used a .0001" (.0025 mm) graduated indicator. Waste of time, I should have borrowed my buddy's .00001" (.00025 mm) indicator. With my .0001" indicator, I had what I call a dead indicator condition No perceivable movement of the indicator dial at all. Consider that .0001" is about 1/30th of a average human hair. This had to be done on a day when the stamping presses out side the toolroom were idle. Press hit's are good for about a .002" bounce of the indicator dial while on the granite plate even through 75' of ferro-concrete.

Geez, that's flat. As far as flat goes, I just measured it to 1/30th of a hair. When you check for light with a flat edge, you are taking it to another level way, beyond what most of the average industrial inspections can detect, in most cases.

Is a 3 stone or 6 or 8 stone process going to get anyone anywhere near where flat needs to be? I'm skeptical.....Convince me this even works......

Experiences or comment?

 

[rbscebu]

Add me to your enquiry.

 

[Pack line]

There is a series of videos on YouTube by oxtools titles "making flat lapping plates". Very good explanation of the whitworth 3 plate method. Will work on 3 surfaces and above. I have done india stones with this method to make precision stones for deburring tooling. It will leave a burnished surface on most stones. May be good or bad depending on the stone.
Probably overkill for a stone tho. You can achieve flatness measured in wavelengths of light. I also use this method to flatten my granite tiles i use for lapping. Granite wears faster then most people would think. That is why sandpaper never touches my surface plates. The back of sand paper is abrasive enough to wear a couple thousandths hole in granite quite quickly.

 

[Gamma]

Iwasaki's team, at one time, used a 6 stone method, you might find the info posted somewhere by a DrNaka on one forum or another. It's a matter of a rotational pattern, not unlike tightening bolts with a torque wrench.
They did say that no matter what, there was always some convexity on one axis or another.
While interesting, I have found much more accuracy, speed, and success with lapping plates.

 

[Pack line]

If i remember correctly, bottom plate is convex, top plate is concave.
When dealing with hones, no temperature or humidity control, and unknown stability, wet dry cycles,etc. it would be an exercise in frustration. Even granite surface plates must be kept in laboratory conditions to receive an AA certification.
If you like to read, there is a book called "the fundamentals of mechanical accuracy" dives way into the weeds of "flatness".

 

[ErieSurfer]

I've seen this mentioned and may have even sought out illustrations, but I haven't completely grasped the concept. Is it even a feasible concept? My basic understanding of it is, if you lap 3 similar stones against each other (loose grit maybe??), you will some how end up with flat stones. Do the stones need to be inspected and orientated according to which way they are out of spec, compared to the stone they would be lapping against?

It all makes it sound so simple and makes me think, if it takes 3 to get flat, and I happen to have, x number greater than 3, and of the same type, then success is guaranteed with excess precision? All I have to do is rub them together, randomly, with some kind of abrasive? Lord I wish it was that simple.

Using my usual, conventional methods, I wanted to test my flattening abilities, or perceived flattening abilities, I took a stone I had recently finished lapping (Black Ark)to work and set it up on the granite inspection plate. I used a .0001" (.0025 mm) graduated indicator. Waste of time, I should have borrowed my buddy's .00001" (.00025 mm) indicator. With my .0001" indicator, I had what I call a dead indicator condition No perceivable movement of the indicator dial at all. Consider that .0001" is about 1/30th of a average human hair. This had to be done on a day when the stamping presses out side the toolroom were idle. Press hit's are good for about a .002" bounce of the indicator dial while on the granite plate even through 75' of ferro-concrete.

Geez, that's flat. As far as flat goes, I just measured it to 1/30th of a hair. When you check for light with a flat edge, you are taking it to another level way, beyond what most of the average industrial inspections can detect, in most cases.

Is a 3 stone or 6 or 8 stone process going to get anyone anywhere near where flat needs to be? I'm skeptical.....Convince me this even works......

Experiences or comment?

I've done it with coticules and BBWs. Works well. The surface finish still needs attention afterwards, but that doesn't bother me. I would think it appropriate for other slates as well, as long as the slates are all of comparable hardness.

I spent 6 hours outside today lapping various hard arks and washitas. Yes, I am a tired puppy. I integrated the 3-stone idea into my work with the hard stones. It seemed to make the whole thing move along quicker if I rubbed a couple stones on each other when submerged in a bucket. I wouldn't want 3-stone flattening to be my only option for hard stones. I also don't think it would work well for stones that are prone to releasing large chunks of their surface, like hindostans. That has happened when I've applied too much downward force while moving across the sandpaper. It bummed me out because it set my progress backwards a bunch.

 

[ErieSurfer]

Iwasaki's team, at one time, used a 6 stone method, you might find the info posted somewhere by a DrNaka on one forum or another. It's a matter of a rotational pattern, not unlike tightening bolts with a torque wrench.
They did say that no matter what, there was always some convexity on one axis or another.
While interesting, I have found much more accuracy, speed, and success with lapping plates.

Are you talking about the kind of lapping plates that might be found in a machine shop, like this one?

Or are you talking about something more like one of these two?

 

[duke762]

Granite wears faster then most people would think. That is why sandpaper never touches my surface plates. The back of sand paper is abrasive enough to wear a couple thousandths hole in granite quite quickly.

YMMV extremely, I did 6 Tans and Blacks on loose grit on my cast (white cast iron?) surface plate at work. Grit on the plate, resurfaced it on the 12" surface grinder and it cleaned up at .0015". I had only caused that much dip abusing it like all get out. I never dreamed that's all it would be. I only used this plate because it was handy and easy for me to renew. Don't use it for much else, in fact.

 

[Pack line]

I just use 4x12x¼" hot rolled steel. A36 i believe. I do a few rows of dimples or slots cut on one side for the course grits and leave the other side smooth for the finer grits. If i have a lot of work to do with course grit i will use a similar sized piece of 3/8 aluminum. The grit embeds into the aluminum a bit "charges" and seems to cut longer. Also got an old DTM plate that is just about out of diamonds, that might be a good option in the future.

 

[Pack line]

YMMV extremely, I did 6 Tans and Blacks on loose grit on my cast (white cast iron?) surface plate at work. Grit on the plate, resurfaced it on the 12" surface grinder and it cleaned up at .0015". I had only caused that much dip abusing it like all get out. I never dreamed that's all it would be. I only used this plate because it was handy and easy for me to renew. Don't use it for much else, in fact.

Just out of curiosity, why not use the surface grinder to flatten the stones? Set up would be a pain but your arms and back would thank you.

 

[Slash McCoy]

The three stone method works fairly well. If you rub two stones together, you might end up with one concave and one convex, and they match perfectly but still they are not very flat. With a three stone round-robin routine, you eventually get your stones fairly flat. Still probably not as good as high quality sandpaper on a granite surface plate, or lapping film on granite, but usually good enough. However, using film or sandpaper is faster and more consistent. I very much prefer a surface that is both wider and longer than the stone, so that overrun can be avoided. I generally use 4" wide sandpaper rolls and my plate is an 18" long piece of 1" thick acrylic from my favorite acrylic vendor, TAP Plastics. I draw a pencil grid on the stone, and lap until it is gone. Then I repeat, rinsing the plate and sandpaper first. Slurry left on the sandpaper can remove the grid before the stone is fully flattened. A second go will fine tune the surface. My granite plate does get used a lot, and it is a cheapie from Grizzly but still certified to .0001" flatness. I think I paid $48 for it and IMHO well worth it even though I am not a machinist. For lapping razor stones, the acrylic I like better, for the long stroke.

Some of my stones I have to lap very frequently, such as my 3k Naniwa which loads up and glazes quickly. I give it a rub with my 1k under running water and it cleans up nicely without going far enough out of flat to notice. A dozen laps is usually plenty but you can see by eye when it is loaded and when it is clean.

 

[Steve56]

Good information. It would be even more useful if most straight razors were actually straight.

How much absolute flatness matters when your 1800s W&B has a tapered spine from decades of honing, a little twist and bend, and an uneven grind, I will question.

I have a Nakayama barber kiita that I’ve never lapped the stamps off, I just use the other side and it isn’t flat. It works fine. Would it work better flat? Maybe, maybe not. For example, if you use a rolling stroke, you’re only contacting a small area of the stone at any time.

 

[Pack line]

Personally i like my stones as flat as possible just because it takes a variable out when honing. Especially if i am using multiple stones. But everyone has their own preferences. Concave, flat, convex whatever gets you there.

 

[rbscebu]

Good information. It would be even more useful if most straight razors were actually straight.

How much absolute flatness matters when your 1800s W&B has a tapered spine from decades of honing, a little twist and bend, and an uneven grind, I will question.

I have a Nakayama barber kiita that I’ve never lapped the stamps off, I just use the other side and it isn’t flat. It works fine. Would it work better flat? Maybe, maybe not. For example, if you use a rolling stroke, you’re only contacting a small area of the stone at any time.

I tend to agree. None of my SRs have a truly straight edge. They all have at least a very slight smile in them. I do however like to keep my whetstones reasonably flat. I use W&D sandpaper on a flat tile for lapping. The constant uniform thickness of the sandpaper can be questioned and takes some of the flatness out of the lapping surface.

 

[duke762]

Begs the question. How flat does flat have to be to do, what needs to be done? I don't trust my jakey vision anymore and would great to have a number, that I can test with instruments, not measured in Angstroms. Straight edge with a small flashlight on a Trans Ark is an exercise in frustration.

Rbsecbu and Pack Line. You both lnow tour wat around precision measurement. Wouldn't it ne nice to have a measurable, number to determine f flat is flat enough?

​

 

[rbscebu]

....
Rbsecbu and Pack Line. You both lnow tour wat around precision measurement. Wouldn't it ne nice to have a measurable, number to determine f flat is flat enough?

It would be interesting but I don't think it would improve the edges I am now getting.

 

[rbscebu]

Some history for you.

Joseph Whitworth (of Whitworth thread fame) popularized the first practical method of making accurate flat surfaces during the 1830s, using engineer's blue and scaping techniques on three trial surfaces, in what is known as Whitworth's three plates method. By testing all three in pairs against each other, it is ensured that the surfaces become flat. Using two surfaces would result in a concave surface and a convex surface. Eventually a point is reached when many points of contact are visible within each square inch, at which time the three surfaces are uniformly flat to a very close tolerance.

 

[Slash McCoy]

You dont "have to" have nice flat stones. But which is better, flat, or not flat? How flat IS flat enough? You really can't put a number to it. The thing is, if you will compromise on one honing parameter, why not another, and another? Why not just randomly swoosh the razor along the top of the stone? Why not just use a Sharp Pebble, or Bear Moo, or even a brick? How much attention to detail is enough? How good is good enough?

To get best possible results, one needs to invest time, energy, and attention into best possible efforts. If you don't want best possible results, hey it's a free country. Just don't wear worry wrinkles in your face over not getting a "good enough" edge, and alles gut. A lot of guys come here looking for help, looking for advice, looking for the way to magically wield the magical razor and get a magical shave. The information is there. There are many parallel paths to a decent edge and a decent shave, but to get the same results as someone else, the obvious thing to do is use the same methods, without compromise. Most of us prefer to make and keep our stones or other honing media as flat as practical. You don't have to, but why not do it?

If you just don't think you have the time or don't want to bother with making your stones flat, you can always switch to lapping film. The plate under the film determines flatness, and it doesn't wear out because the razor doesnt even touch it.

 

[Legion]

If only using two, and one is steel with diamond attached, how is it going to get convex or concave. That is good enough for me.

Paper on glass, the same, to an acceptable degree for honing razors.

The three stones is an interesting intellectual process, but really, just use one flat surface that doesn't wear, to flatten the one that does.

 

[Pack line]

Begs the question. How flat does flat have to be to do, what needs to be done? I don't trust my jakey vision anymore and would great to have a number, that I can test with instruments, not measured in Angstroms. Straight edge with a small flashlight on a Trans Ark is an exercise in frustration.

Rbsecbu and Pack Line. You both lnow tour wat around precision measurement. Wouldn't it ne nice to have a measurable, number to determine f flat is flat enough?

​

In a perfect world it would be nice to have instruments and numbers but i would think it would be cost prohibited and frustrating for most. Not to mention we are dealing with a substrate of unknown stability, as anyone with a certain brand of stone can attest to. One wet dry cycle and it is a potato chip. Personal i like to us a straightedge and light source in the jolly roger pattern. Moving the light source away from the substrate with help remove the frustration of translucency.