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

There goes your controversy!

Originally Posted by gssixgun

I think everybody realizes that the 3 stone method works (even if we don't use it for SR honing ), the question seems to be "Why the 2 stone method doesn't"

Because it is not done carefully enough to avoid the anisotropy from the ergonomics of hand lapping.

Originally Posted by bluesman7

I did it because I liked the concept. Two surfaces that mate with random motion can only be spherical with flat being a sphere of infinite radius.

My xfig is broken so with 5min on a new to me program called inkscape I can only produce a rather rudimentary illustration:


The blue and the red areas are meant to represent the two hones and if you slide them around only along the green line they can stay spherical. But any force component away from that ideal spherical plane would be decreasing their common curvature and making them flat. I.e if you try to move them along the white line direction while they will still slide relative to each other along the sphere the abrading forces would be converting that spherical surface into a plane.

Originally Posted by gugi

Because it is not done carefully enough to avoid the anisotropy from the ergonomics of hand lapping.


My xfig is broken so with 5min on a new to me program called inkscape I can only produce a rather rudimentary illustration:


The blue and the red areas are meant to represent the two hones and if you slide them around only along the green line they can stay spherical. But any force component away from that ideal spherical plane would be decreasing their common curvature and making them flat. I.e if you try to move them along the white line direction while they will still slide relative to each other along the sphere the abrading forces would be converting that spherical surface into a plane.

AHA! NOW I understand!

Originally Posted by sharptonn

There goes your controversy!

You can always listen to Prince for Controversy

Originally Posted by sharptonn

AHA! NOW I understand!

Yeah, as they say a differential equation is worth all of its derivatives in quadratures and that's even without the Sturm–Liouville theory

Dems don't call 'er 'advanced honing topics' fer nuthin'

Originally Posted by fairwoodworking

Again, this may only relate to woodworking... We use a 1k stone for quick material removal anyways. So the coarsest stone would be the obvious and cheapest stone to achieve flat with. I then use the 1k stones to flatten the 4k and 8k stones.



Think Rock, Paper, Scissors. Great game because each option wins against one other, but also looses to one other.

Now lets play Rock, Paper. Super lame game because Paper always covers rock, and rock can never win.

With two stones they will wear to mate perfectly to each other, but a perfect match is not necessarily flat. Think spoons.

This is a really hard thing to explain, kinda like explaining what the color blue is.

There was a time that the progressive lapping was popular here using the 1k to lap the 4k to lap the 8k but it fell out of favor rather quickly..

Are you still using the 3 stone method when lapping the 4k and the 8k ????

What I was really asking was why would you need 3 flat 1k hones,, I always figured it was because you dish them much faster then a SR honer does ???

Originally Posted by onimaru55

You can always listen to Prince for Controversy

Indeed! Prince - Purple Rain (1984) - MusicPlayOn

Originally Posted by gugi

Because it is not done carefully enough to avoid the anisotropy from the ergonomics of hand lapping.

This is true and exactly why it doesn't work



The blue and the red areas are meant to represent the two hones and if you slide them around only along the green line they can stay spherical. But any force component away from that ideal spherical plane would be decreasing their common curvature and making them flat. I.e if you try to move them along the white line direction while they will still slide relative to each other along the sphere the abrading forces would be converting that spherical surface into a plane.

Nobody laps using only one direction... but you know that, and it also doesn't matter

After doing way more reading then I ever wanted to about the subject (I will never use), it is quite clear that you are wrong, in fact the principle was applied years ago to make convex and concave surfaces for lenses out of flat surfaces ..

From my reading,, it is quite simple to explain and understand ..

"The reason is that when the pieces aren't directly over each other the same amount of downward force exerts a greater pressure on the portions that are still in contact, causing more material to be ground away at the edges of one piece to produce a convex surface, and from the center of the other to produce a concave surface."

Now you all can do the reading yourselves, two simple searches on the internet will yield plenty of papers out there about

the 3 Surface lapping method
and
the 2 Surface lapping method


What does work is using a surface that doesn't abrade (DMT) and a surface that does (a Hone) and even then you have to be careful ...

Originally Posted by gssixgun

Nobody laps using only one direction... but you know that, and it also doesn't matter

After doing way more reading then I ever wanted to about the subject, it is quite clear that you are wrong, in fact the principle was applied years ago to make convex and concave surfaces for lenses out of flat surfaces ..

From my reading,, it is quite simple to explain and understand ..

"The reason is that when the pieces aren't directly over each other the same amount of downward force exerts a greater pressure on the portions that are still in contact, causing more material to be ground away at the edges of one piece to produce a convex surface, and from the center of the other to produce a concave surface."

That's how you can get it wrong when you don't understand the process and how to tell which of several competing factors dominates. What you looked up is about rubbing together surfaces that are one order of magnitude smaller than lapping hones.
The surface to volume increases with the decrease of radius and you are in a very different regime where the two rubbing areas are only slightly overlapping most of the time.

Bottom line is that by rubbing two objects together you can either make concave/convex pair of surfaces or you can make flat surfaces. If you understand how it works you can pick one or the other by rubbing them in a way that emphasizes them becoming flat or them becoming curved. If you don't you argue ad infinitum that your newly discovered internet bit knowledge is the absolute truth out there.

With human sized lengthscales (2-20cm) and forces (10-10000g) you can span the two regimes on ordinary materials (typical glass/stones/metals).

Originally Posted by gugi

Bottom line is that by rubbing two objects together you can either make concave/convex pair of surfaces or you can make flat surfaces. If you understand how it works you can pick one or the other by rubbing them in a way that emphasizes them becoming flat or them becoming curved.

And yet there are 100's if not more references that disagree.. The closest I found to your Hypothesis is that it might be possible to get/keep two flat surfaces, flat, although unlikely, especially when doing it by hand...

Since I am not going to try it myself, I am going to have to go with the majority and lengthily consensus on this one, you can believe what you chose...

Seems that nobody is arguing that the 3 surface system works, at least not that I found anyway... Not that I plan on trying it either...