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  1. #21
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    You really need to be dedicated.

    I did 3 angle plates, small ones, and that was plenty enough time and effort for this boy, even using a granite flat to level the surfaces from time to time..

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    This is just my light weight input but I've read of using three sharpening stoned, AO I believe, to get stones flat. I read this on one knife making site or another.
    The subject of flattening oil/whet stones is nearly as controversial as any.
    This is just what I've read, never tried it. I use a concrete block on the rare occasions that I feel one of my stones is to blame for my poor sharpening job. Whitworth-three plate method I'm not inclined to believe a stone used for sharpening a knife needs to be within a tolerance they naked eye can't see. JMOHO

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    Quote Originally Posted by multimc22 View Post
    Thanks Paolo,

    I've given it a try tonight, not using any lapping compound just water with a bit of detergent in it and lapping them against each other, 3 plate method. And the results......well three very sad, misused and abused stones from the work shop, gummed up with years of crap, are all very clean and "flat" and looking like new! Worked on 'em for about hour and half. I won't try to define how "flat" but I can certainly take all of the high spots/damage marks off the drill press table without actually marking up the original machined surface. I surprise myself, and yes I was inspired to try this after having a look at Tom Lipton's vid.

    Thanks for the replies guys,

    Ian Mac.
    How do you know they were flat ? And what is flat ( for you ) ? And how did you test for flatness ? Sure, you can flatten 3 stones by rubbing them but I would not expect them to be lambda/10. You can do by hand and more or less in the kitchen some amazing stuff flatness wise. But grinding wheels keep losing particles and that's a big problem.

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    Quote Originally Posted by JST View Post
    You really need to be dedicated.

    I did 3 angle plates, small ones, and that was plenty enough time and effort for this boy, even using a granite flat to level the surfaces from time to time..
    Indeed. Another option is to take them to a place with a good hydrostatic grinder and have them ground those plates flat. You can beat that in theory but it's not worth the trouble.

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    Quote Originally Posted by AlexO View Post
    How do you know they were flat ? And what is flat ( for you ) ? And how did you test for flatness ? Sure, you can flatten 3 stones by rubbing them but I would not expect them to be lambda/10. You can do by hand and more or less in the kitchen some amazing stuff flatness wise. But grinding wheels keep losing particles and that's a big problem.


    If they will mark each other evenly all over the surface, when applied in random orientations, and combinations, they ARE flat. If A and B print 40 PPI against one another, you do not know much. They might be concave and convex, or look like a potato chip.

    If A and B both print 40 PPI against C, now you know they must be flat. A could be convex and fit a concave B, but C cannot be both convex to fit B and concave to fit A. They must all be flat, they cannot be curved any more than part of the thickness of the marking medium, or the markings would show up lighter and darker in a corresponding pattern.

    Using the "alcohol haze" method (which I have never done) is allegedly capable of extremely thin coatings and consequent low error marking. Exactly HOW flat (in numbers) is something that has to be measured separately, but all three of them will be "that flat".

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    Well they achieved the result I was looking for, as I said, I was able to clean up the marks from impact damage on the drill press table without interfering with the machined finish so that's "flat enough".

    Cheers, Ian Mac.

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    Quote Originally Posted by JST View Post
    If they will mark each other evenly all over the surface, when applied in random orientations, and combinations, they ARE flat. If A and B print 40 PPI against one another, you do not know much. They might be concave and convex, or look like a potato chip.

    If A and B both print 40 PPI against C, now you know they must be flat. A could be convex and fit a concave B, but C cannot be both convex to fit B and concave to fit A. They must all be flat, they cannot be curved any more than part of the thickness of the marking medium, or the markings would show up lighter and darker in a corresponding pattern.

    Using the "alcohol haze" method (which I have never done) is allegedly capable of extremely thin coatings and consequent low error marking. Exactly HOW flat (in numbers) is something that has to be measured separately, but all three of them will be "that flat".
    I apologize but I don't understand a thing - what IS this about ???

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    Quote Originally Posted by multimc22 View Post
    Well they achieved the result I was looking for, as I said, I was able to clean up the marks from impact damage on the drill press table without interfering with the machined finish so that's "flat enough".

    Cheers, Ian Mac.
    Well, you seem to have aimed very very low. You don't need to use the three plate method ( FOR CARBORUNDUM STONES ) to flatten a drill press table.

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    Ignore the snide remarks...

    I have used the three plate method to make flat surfaces and I've also used it with the aid of those flat surfaces to make squares with a guaranteed 90° angle. It wasn't a production job, it was to see how easy it would be to do. The squares were, however, later used as masters to check the angle of some lathe bed shears.

    I also use the three plate method to maintain flatness on my sharpening stones. You don't want to cut the individual grains, that results in a polished lump of carboundum, not a flat, clean cutting stone. You do need to have three stones of the same grade ideally. plenty of water to flush the detritus away makes the job simple.

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    I agree with having three square or round plates to begin with, having lapped three rectangular 12"x18" granite blocks to each other in all possible combinations. Like JST mentions in an earlier post, If the objects are rectangular there are two possible geometries that will mate with all three surfaces: a completely flat surface and one that is curved across the diagonals a bit like a saddle or a Pringles chip (exaggerated).

    This can be eliminated if you have round or square flats by simply rotating 90 degrees during the lapping so that the high spots on both surfaces rub together during lapping. I found a figure 8 lapping pattern automatically generated the curved potato chip surface and used only straight strokes after. I called the job done once I could measure a half micron height difference with a Sylvac digital indicator mounted between three ball bearing rests 8 inches apart. That translates to a 2 micron worst case deviation over the 16" of the diagonals using sagitta maths.

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    Another thing to watch out for is, when your rubbing them don't move them out to far. I try to only move it a 1/2" out or off the other one your lapping. When I was an apprentice (I'm guessing 17) I got the job of lapping 3 - 12" round lapping plates used by Control Data. It was a boring, heavy lift, tiring job but the Journeymen made me do it. LOL....I also would turn it 90 degree's during the lap. We used Clover Lapping compound course first and then Fine as it got better. The final checks we did was with a thin layer of Dykem paste bluing. After that I wore bluing for a few days.

    I took these pic's out of the Moore Book. They still sell these books through Moore Special Tools.
    Sorry for the fuzzy pic's. Took them from my Moore Book. It's a great Hard Cover book. I put the forward and cover pages, so you know where to buy one. The book is a great book and they talk about scraping, temp control,testing, etc. Rich
    Attached Thumbnails Attached Thumbnails 20171030_091919_resized.jpg   20171030_091940_resized.jpg   20171030_091900_resized.jpg   20171030_091851_resized.jpg  

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    More Moore Pictures
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    Quote Originally Posted by AlexO View Post
    I apologize but I don't understand a thing - what IS this about ???


    Obviously it is about how you know they are flat........ Because the only geometry that will mark 3 plates evenly in random orientations IS flat.

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    Quote Originally Posted by JST View Post
    Obviously it is about how you know they are flat........ Because the only geometry that will mark 3 plates evenly in random orientations IS flat.
    Well, you surely don't expect that to work for carborundum stones... That's what we were talking about : getting three carborundum stones flat to flatten a pedestal drill table. This is unnecessary - on stone suffices and it's flat by definition. There is absolutely no need to flatten it further.

    It's called a CUP grinding stone.

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    Quote Originally Posted by Mark Rand View Post
    Ignore the snide remarks...

    I have used the three plate method to make flat surfaces and I've also used it with the aid of those flat surfaces to make squares with a guaranteed 90° angle. It wasn't a production job, it was to see how easy it would be to do. The squares were, however, later used as masters to check the angle of some lathe bed shears.

    I also use the three plate method to maintain flatness on my sharpening stones. You don't want to cut the individual grains, that results in a polished lump of carboundum, not a flat, clean cutting stone. You do need to have three stones of the same grade ideally. plenty of water to flush the detritus away makes the job simple.
    Mark,

    I didn't know if it was a valid process, just sort of made sense to give it a crack, but as you have validated it and Mr King likes it then that's plenty good enough for me.

    Thanks for your input, appreciated.

    Ian Mac.

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    Quote Originally Posted by multimc22 View Post
    Mark,

    I didn't know if it was a valid process, just sort of made sense to give it a crack, but as you have validated it and Mr King likes it then that's plenty good enough for me.

    Thanks for your input, appreciated.

    Ian Mac.
    No, it did NOT make sense to "give it a crack". Nor can you generate a flat surface by rubbing with a carborundum disk. It may work for your limited purpose but it's just not good ... procedure. I appreciate that not everybody needs flat within half a tenth but we shouldn't add to confusion. "Works for me" doesn't mean much a lot of times.

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    Quote Originally Posted by AlexO View Post
    Well, you surely don't expect that to work for carborundum stones... That's what we were talking about : getting three carborundum stones flat to flatten a pedestal drill table. This is unnecessary - on stone suffices and it's flat by definition. There is absolutely no need to flatten it further.

    It's called a CUP grinding stone.


    Dunno there, Alex.... the first post in the thread was:

    Quote Originally Posted by challenger View Post
    I know that it makes no sense to use the three late method to generate a precision plate. Still I'm curious about it.
    What would someone use for the plates? In other words what do you start with? Where does one look for three slabs of CI plate of similar sizes?
    Thanks for the patience. Whitworth-three plate method

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    Quote Originally Posted by JST View Post
    Dunno there, Alex.... the first post in the thread was:
    That was in February. Last post of that discussion was on April 1st. Then, seven months down the line "multimc22" asks "If I have three 8" carborundum stones, apply the three plate method to them will I achieve the equivalent of precision ground stones?".

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    I am puzzled by one aspect of the Whitworth method.

    Conventional wisdom (as gleaned from a variety of websites and videos) seems to say to start the process with B on A, and then switch to A on B. In other words, start with B stationary and lap A on B, and then set A to be stationary and lab B on A.

    For example, The Whitworth Three Plates Method — Eric Weinhoffer says,"To begin, the Red and Green plates are lapped against each other in an alternating manner. That is, one plate remains stationary while the other is lapped against it, and then the opposite is performed:"

    I can't get my head around the need for the "alternating manner" and what difference it makes which plate is stationary and which is moving. The two plates are moving relative to each other irrespective of which one is stationary. Moving A 'south' 20mm is the same as moving B 'north' 20mm. Likewise, rotating A 30 degrees clockwise is the same as rotating B 30 degrees anti-clockwise.

    What would the situation be if both plates were moving relative, not only to each other, but to some other fixed point. For example, if I held the one plate in each hand and rubbed the plates against each other by moving both my hands. I can't see how it would make any difference if I swopped the plates from one hand to the other, so I can't see why it makes a difference if one plate is stationary and one is being moved.

    Clearly, I am missing some fundamental understanding of the lapping process or some other fundamental, so please could someone fill in the gap in my knowledge.

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    Further to my previous post....

    Why does the alternating apply to only the first step (A on B then B on A) and not on the subsequent steps (C on A, C on B, etc)?


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