How did barbers hone a wedge in the olden days?

[QUOTE=gugi;1497325]I don't know, counting is too hard for me. I will wait for one of the math geniuses to come back and explain it to me or point me to google [QUOTE]
[ATTACH=CONFIG201372[/ATTACH] https://WWW.GOOGLE.COM.AU

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Originally Posted by gssixgun

To be accurate it works, and has worked for many years, why the 3 and not 2 ???
I would guess that over the years they figured out that 2 stones will begin to mirror each other, at least that is what I have read...

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Even with one concave and one convex stone that mirror each other rubbing them together will make them flat. The abrasive force is larger when the apex of the convex hone rubs against the sides of the concave one than when they are in the 'matched' arrangement, so as the lapping progresses the two surfaces become flatter and flatter.

Of course, as it's been pointed out countless of times this is irrelevant for most people nowadays because we use diamond plates that are much tougher than the hones we lap with them.

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Originally Posted by Kees

When I buy a cupped hone on the bay 1st thing I do is lap it flat on the kitchen work top with one piece of sandpaper. Works a treat. Would it be better if I use 2 different worktops and 2 pieces of sandpaper?

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It would be better if you didn't buy a cupped hone to begin with,,,,,,,,,,,:D

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Originally Posted by gugi

Even with one concave and one convex stone that mirror each other rubbing them together will make them flat. The abrasive force is larger when the apex of the convex hone rubs against the sides of the concave one than when they are in the 'matched' arrangement, so as the lapping progresses the two surfaces become flatter and flatter.

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I know that sounds logical, it sure does to me, but it isn't what is written nor recommended, somewhere along the years of people actually doing this they found out that three surfaces worked better then two, and six worked even better...

I don't know why, nor do I really care since I don't use the method, but like many other methods that have been proved over time, if I were going to use it I would try it first by following the directions and going from there...

Much like we tell newb SR honers to use the X-stroke "Because it works"


Making Accurate Straight-Edges from Scratch

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Originally Posted by Hirlau

It would be better if you didn't buy a cupped hone to begin with,,,,,,,,,,,:D

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What about a honed cup?

Do we really want our cups honed ?? :shrug:

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Originally Posted by Hirlau

Do we really want our cups honed ?? :shrug:

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Dunno sounds preferable to having my hups coned :)

They're gonna swat us in a minute Ed,,, you got me in trouble again,,,

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Originally Posted by gugi

Even with one concave and one convex stone that mirror each other rubbing them together will make them flat. The abrasive force is larger when the apex of the convex hone rubs against the sides of the concave one than when they are in the 'matched' arrangement, so as the lapping progresses the two surfaces become flatter and flatter.

Of course, as it's been pointed out countless of times this is irrelevant for most people nowadays because we use diamond plates that are much tougher than the hones we lap with them.

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It is pretty irrelevant for most folks nowadays, and nobody I saw was advocating using the method over a diamond plate for flattening stones. What I take issue with is the blatant misinformation being spread around. Rubbing two stones together will NOT result in flat surfaces. As they are rubbed together, one will take on a concave spherical surface and the other a convex spherical surface. This is a fact, not an opinion, despite all the pecking by you and the guys that are like old mother hens around here.

Try reading a factual reference book, like "Foundations of Mechanical Accuracy" by Wayne R. Moore. Or even search for it yourself. Since you are such a tinfoil hat conspiracy theorist regarding Google (oops, found it with Google!) and I know you won't be buying the book, try this link written by a CWU scholar. Section 4.3 is the pertinent information to 3 stone or item flattening, but the rest is good reading for anyone interested in lapping.

https://www.google.com/url?sa=t&sour...KB5GGRbS4v_DRA

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Originally Posted by gssixgun

I know that sounds logical, it sure does to me, but it isn't what is written nor recommended, somewhere along the years of people actually doing this they found out that three surfaces worked better then two, and six worked even better...

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A recommendation is only as good as the recommender. When guys on military missions in the jungle have been both trained and successful in lapping two stones flat it doesn't really matter to me that a desk jockey insists three is the minimum number needed.

We've all heard plenty of 'old wisdom' that is pure garbage and plenty that isn't.
In my book understanding is always better than not understanding but I have zero interest convincing people they're wrong. Everybody is free to do things any way they like - the dumb way may just as well get you to the same place as the smart way would.

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Originally Posted by gssixgun

Making Accurate Straight-Edges from Scratch

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This isn't the process of lapping hones by rubbing them together, but rather something completely different. It is a process for verification that a flatness is achieved You keep one surface as 'reference' and remove material from the other by some means, then you check against the reference if there are any 'gaps'.
There is no motion whatsoever between any two surfaces he is looking at. If you allow motion you'll clearly see the gaps even with two surfaces and you don't need three:
Attachment 201383


Three surfaces are absolutely necessary for verifying flatness (i.e. zero curvature) by static matching, but they are not necessary for achieving it.