3 Stone Flattening Method??

[Pack line]

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.

It is an interesting intellectual concept, but as pointed out by @rbscebu in a previous post, it was originally used to make a reference surface not a finished part. A machinist lapping a part will use a lapping plate to do so, not a reference surface. Essentially a substrate commonly impregnated with an abrasive. The lapping plate or part would periodically be checked against the reference surface for flatness but never lapped against it.
In our world, the part is a hone, the lapping plate is a diamond plate, tile and wd, glass and SiC, etc and the reference surface could be a straight edge.

I guess that was a really long winded, pontificating way to say i completely agree with you but it is early and i have not had any coffee yet.

Also a side note, for the 3 plate method to be completely effective the parts need to be matched on at least 2 axis. Not really effective on a rectangle as you can not get full contact when your bottom stone is laying north south and your top stone is laying east west.

 

[duke762]

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.

I think trying to grind a Trans/Black Ark could turn in to a tedious disaster. I'd be worried about heat build up at the point of contact causing possible micro fractures even with coolant. Lovely idea though.

So now I will be scrounging around the shop looking for a diamond wheel trying to figure out how I'm going to try this. Yeah, got to try this......

 

[Pack line]

I think trying to grind a Trans/Black Ark could turn in to a tedious disaster. I'd be worried about heat build up at the point of contact causing possible micro fractures even with coolant. Lovely idea though.

So now I will be scrounging around the shop looking for a diamond wheel trying to figure out how I'm going to try this. Yeah, got to try this......

On second thought, try a cheap combo stone first. The thought of a nice ark flying across the shop like a missile is giving me heart palpitations...

 

[ErieSurfer]

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?

My eyes are like yours. I mentioned the stone lapping work earlier in this thread. All of the work was done outdoors and the bright blue sky was my backlight source. I was wearing my contacts combined with reading glasses that day. Flash forward to yesterday. I'm working a razor and I can't figure out why my recently-lapped hard ark isn't improving the bevel. The loupe tells me I'm not hitting the bevel. I grab my straightedge and use the overhead kitchen fixture as the backlight. I'm wearing my prescription glasses and set them aside; no lenses involved. What do I see? The frickin' stone is very mildly convex!

How flat IS flat enough?

Indeed. And how do you ascertain that suitable flatness has been achieved? When is the flattening done? How do you know?

A dependable reference to judge when the stones are correctly flat is key. I'm not a machinist, so if there is some practical way to fabricate a common item into a suitable reference edge for checking flatness, I'm all ears. For example, can you take the steel ruler off of an adjustable carpenter's square and sand the edge true with 1500/2000 grit sandpaper on granite? Does that result in a reference tool that is not just good enough, but better than what is needed?

My existing straightedge may be fine as it is. But how would I know?

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.

What is the 'jolly roger pattern'?

 

[duke762]

I use conventional methods to flatten but always curious about other methods to achieve flatness and how to measure it. I use a straight I ground myself using all the precision tricks I've learned over the years. It is flat. Checked it with a .0001" indicator, no dial movement. I put it on the granite plate and checked for light, no light. This is as flat as I'll ever be able to get anything and this is what I check my stones with. I just don't trust my eyes like I used to.

 

[Pack line]

@ErieSurfer British flag pattern. Straight edge left to right: top, middle, bottom, do the same up and down, then diagonally in both directions.
Depending on your location, a proper straight edge can be found inexpensively. This is not a ruler, it is a piece of metal, around 1/4 inch thick with one precision ground edge. Most machinist squares will also have a precision ground edge and are easier to find in shorter lengths. 12 inch is about all you need unless you have some monster stones.
If you have trouble seeing light just lay the stone on the bench and check it with the straight edge in the same pattern using a piece of paper like a feeler gauge. If you can slide the paper between the two there is at least a 0.004 inch gap. If not, your stone is flat to within 0.004 inches.
Straight edge can also be checked against a granite plate using the paper method.