Thread: How did barbers hone a wedge in the olden days?

Great entertainment in this thread- I really enjoyed reading it, even if I don't fully understand all of it.

Originally Posted by gugi

If you rub two stones together in different directions they will end up both flat. You can only keep a curvature if you don't move the two pieces relative to each other in the direction of that curvature, e.g. two cylinders that you slide only along their common axis.

This is what your statement was that started all of this. It is incorrect.

Originally Posted by mainaman

After several lapings hone #2 developed a dish similar to hone #1 which did not improve from its original state. Basically what would happen is grit will accumulate between the two hones in the middle and will create a dish.

This looks rather odd. You have two hones that are of the same material, one with a hump one flat, you rub them together and the material is removed at much larger rate from the flat hone and the dish that is developing than from the hump.

You don't get unaccounted broken symmetries like this. Somebody has an explanation that is not optical illusion i.e. 'far easier to note the change in the flat surface than the equivalent change in the curved surface'?

Originally Posted by bluesman7

This is what your statement was that started all of this. It is incorrect.

It is not incorrect. Spend enough time and don't fall in the pitfall of anisotropy or extreme boundary effects and they will be flat. Have you ever seen/heard of a rotating lapping plate develop curvature that is not radial? It's the exact same reason that two hones rubbed together end up flat eventually.

Originally Posted by gugi

This looks rather odd. You have two hones that are of the same material, one with a hump one flat, you rub them together and the material is removed at much larger rate from the flat hone and the dish that is developing than from the hump.

You don't get unaccounted broken symmetries like this. Somebody has an explanation that is not optical illusion i.e. 'far easier to note the change in the flat surface than the equivalent change in the curved surface'?
.

That is why I think the test I did is inconclusive, the grit that accumulates between the hones is a variable that plays significant role in the process IMO.
It takes way too much time to lap like that to get any meaningful result.

Originally Posted by eKretz

Checking across the diagonals and in 3 places along the longitudinal axis will give you a pretty good idea.

This is also what I was thinking ...

How about using the 1 hone method with a bit of wet n dry. Prolem solved.....

Originally Posted by mainaman

That is why I think the test I did is inconclusive, the grit that accumulates between the hones is a variable that plays significant role in the process IMO.
It takes way too much time to lap like that to get any meaningful result.

The removal of material should still be symmetric to first and probably second order (the centrifugal force does result in a slightly faster abrasion from the concave side than from the convex but it should be negligible for your case).
Of course if you start with one flat and one humped surface you'll first end up with matching concave convex surfaces but continuing further will flatten those. The superstones seem softer than the chosera, that's why I had my eye on them as a test case, but even they may end up too time consuming.
And yes, attenuation of the long wavelength noise is typically the most time consuming part, hence when people see 'smooth' happen way before 'flat' they may end up mistakenly thinking that flat never happens.
Three hones I think speed up the process of the long wavelength attenuation, but I haven't yet thought out how to quantitatively calculate that speed up. Seems like a moderately interesting problem, though, and may even end up relevant for my research so I'll be thinking more about it.

Originally Posted by gugi

We are talking about hones that are flat for the purpose of honing razors. Lapping them on DMT 325 is perfectly good for this purpose, so that is a good benchmark to test against. If you want to argue that that's not flat enough and you'll get better edges from flatter hones, start a separate thread where this can be explored on its own merit.

I wasn't, in fact I have said that repeatedly "This is not relative to honing razors"

I was arguing the 3 Stone system -vs- your claim that 2 stones will do the same..

I think after the last several posts I see your disconnect, but if you had simply read the 3 stone method descriptions we might all have saved a ton of typing...

I am pretty sure that rubbing 2 like stones together will not result in flat, what I am not convinced of is that it will result in Convex and Concave surfaces .. That part I have to see for myself...

Originally Posted by gugi

The removal of material should still be symmetric to first and probably second order (the centrifugal force does result in a slightly faster abrasion from the concave side than from the convex but it should be negligible for your case).
Of course if you start with one flat and one humped surface you'll first end up with matching concave convex surfaces but continuing further will flatten those. The superstones seem softer than the chosera, that's why I had my eye on them as a test case, but even they may end up too time consuming.
And yes, attenuation of the long wavelength noise is typically the most time consuming part, hence when people see 'smooth' happen way before 'flat' they may end up mistakenly thinking that flat never happens.
Three hones I think speed up the process of the long wavelength attenuation, but I haven't yet thought out how to quantitatively calculate that speed up. Seems like a moderately interesting problem, though, and may even end up relevant for my research so I'll be thinking more about it.

There is also the issue with uneven down pressure due to how the hones are positioned in the sink.
Then there is the variable of how the hones move with respect to each other, circular motion, x-motion, 8's. this experiment has to be defined very carefully for consistency.
I just do not want to spend a ton of time going all the way. I am glad we have DMTs and Atomas these days.

Originally Posted by mainaman

There is also the issue with uneven down pressure due to how the hones are positioned in the sink.
Then there is the variable of how the hones move with respect to each other, circular motion, x-motion, 8's. this experiment has to be defined very carefully for consistency.
.

And there you have the exact reasons for the 3 stone system, it allegedly eliminates all that, I haven't used it so I can't say for sure...