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  1. #1
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    Default Precision Flat Stones

    Robin Renzetti's video first alerted me to these magical devices!
    YouTube
    I had my local grinder make a set for me which I have really enjoyed. Then I realized that Stefan Gotteswinter had made some with different shapes!
    Diamantgeschliffene Abziehsteine – Stefan Gotteswinter
    I was really excited about the 45 degree ones for some of the reconditioning I had to do to my creaky old brown and sharpe mill.
    Unfortunately Stefan won't ship outside the EU. And even though Richard keeps inviting me along for camping trips, I didn't think he wanted to mule some back from Austria after his next class.
    So I had some made.
    I have 2 sets that aren't spoken for. They are ground on the diagonal faces and the two faces adjacent to them. The short ends and the "back" are the original roughness.
    They are $200 shipped priority in the continental US. If you are somewhere else, let me know and I can figure shipping.
    If there are a lot of other people who want these or just the regular flat stones I can make another run.

    Hahn Rossman
    Attached Thumbnails Attached Thumbnails img_20200507_143853.jpg   img_20200507_143841.jpg   img_20200507_143831.jpg  

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    Are these diamond plated? That price is a bit excessive, ain't it? And this isn't the "for sale" forum...

    I think I need to get into the flat stone racket.

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    Hahn,

    Thanks for posting the video link to Robin’s work. He has to be one of the most meticulous craftsman I am aware of. Those stone look to be very useful and interesting. I can see pulling out a lot of what I think are beautifully finished surfaces and trying them with the stones only to be disillusioned. Slicking those surfaces down with ground stones would become addictive.

    Denis

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    You can buy ground stones from Spencer [email protected] and Lance Baltzley. Adam booth did a great you tube show on ground stones. YouTube

    I spoke to Robin and he said flat stones were not his idea. He had used Professional Instruments/ Air bearings Inc. stones who has been making and selling them for years. Flatstones rev 2.pdf - Google Drive

    Products - PiCoAirbearings

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    what is the intended use for the stones? correcting ways? how flat are they? a good file like "valorbe" will be very straight and doesnt need any service like the stones.

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    Why did you use combination stones vs one grit? The first one I made was around 1993 so not a new idea at all, although I was just trying to level it and figured the surface grinder was the best way to do it that I had easy access to.

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    Lance and Spencer sent me a set to test. They help after you get 20 PPI on a straight-edge as they stone the high spots down to the same plane. Prior to 20 PPI the regular unground stone works just fine. The ground stones get so smooth and they don't cut as well. The tapered stones I hand out in the classes are bent, some are high in the middle as much as .010". I buy them from MSC ( see below) I suggest you hinge the stone your using so you know if they are flat. Pictures are the stones I use. dsc01892.jpgdsc01891.jpgdsc01887.jpg

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    eKretz-

    Check out the video if you haven’t already. My recollection is Robin talks to the fact that the commercial ones from Professional Instruments were significantly more than $200. I’m half-way through making a set of my own and I can attest that there is a significant amount of labor involved in getting from a regular set of Norton stones ($50 for a pair) to a set of precision ground stones. Much as there is a significant amount of labor involved in getting from a chunk of tool steel to a precision 1-2-3 block.

    $200 doesn’t seem excessive to me, which is saying a lot coming from a dumpster diver. ��

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    Out of curiosity is it the fact they are flater or the abrasives all have flats ground on them so they don't cut that makes them so desirable? Or is it both? You can lap them flat with loose abrasive on a relatively flat plate, but they will cut well since the abrasive in the stone is as sharp as possible.

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    I made a number of precision stones for different people a few years ago and was able to make a good profit at $190/pair for 6 stones (3 sets) at a time. I'm not the most efficient with the process and there are people that could do the same work much faster I imagine (took me about 1.75 hours/pair after setup). I'm not normally set up to do the grinding of the stones so it takes me about an hour to get setup, true and dress the diamond wheel and start grinding. Of course, the first set I messed around with variables for about two days trying to get the process down.

    I use the hell out of my set everyday I'm in the shop and they've been a great addition to the toolbox. Highly recommend!

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    Yeah, like I said, seems excessive. This isn't like grinding hardened steel. It's comparatively easy to grind a sharpening stone with diamond abrasive. (Yep, have done it). The cost is especially excessive to me when the same benefit can be had by flattening the sharpening stone with a diamond plate. (Yep, have done it). This is one of those things that is really so simple there's no reason not to do it yourself - unless you're so busy that you just don't have any free time.

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    Quote Originally Posted by DavidScott View Post
    Out of curiosity is it the fact they are flater or the abrasives all have flats ground on them so they don't cut that makes them so desirable? Or is it both? You can lap them flat with loose abrasive on a relatively flat plate, but they will cut well since the abrasive in the stone is as sharp as possible.
    The advantage is low tool pressure (due to the entire surface being on the same plane) and therefore no scratching or gouging of important surfaces while stoning. They efficiently remove burrs without changing the geometry which could occur with non-ground variants. Of course special care with a non-ground variants works and has worked for over a hundred years but by diamond grinding you open up some possibilities that otherwise wouldn't fly.

    I'd recommend watching Robin Renzetti's videos (all of them are pure gold in my opinion) for a more in-depth look at the applications.

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    I'm not sure I understand the mechanism at work here. There are two mechanical ways to get rid of asperities: remove the metal (e.g. grind, hone, or lap) or push it down into a low spot (e.g. burnish). You can also use electrical or chemical methods, or a combination of two or three methods.

    In Robin's video, he grinds the stone flat with a diamond wheel, uses it dry, and refers to it as burnishing, saying it doesn't actually remove any metal. He then compares it to a regular, unground stone, also dry. Stefan's website also explicitly says to use it dry.

    I was always taught to stone things wet; we usually used LPS-1. I'm not sure that particular lubricant was a considered decision, so much as there was always a spray bottle of it around.

    A few possibilities that occur to me:

    1) The flatness actually matters. What makes me think this case is less likely is Robin's example of stoning a toolholder. With a convex target surface, the flatness of the stone should be irrelevant. The difference in curvature between the stone and the toolholder is roughly the same whether the stone is perfectly flat or out .010"

    2) The grains are ground flat and the stone is acting as a burnisher. The video examples where there are raised dings, however, definitely make it seem like there is cutting action going on at the dings.

    3) The grains are ground flat and burnish at low pressure, cut at high pressure. For the 'already flat' portion, they don't have enough pressure to cut, but where there's a high spot, the local pressure is high enough to cut.

    4) The grains are only cutting, but the diamond grinding decreases the effective size of the abrasive grains.

    Sadly, I no longer have access to an atomic force microsope, as this raises a number of interesting questions.

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    Quote Originally Posted by eKretz View Post
    Yeah, like I said, seems excessive. This isn't like grinding hardened steel. It's comparatively easy to grind a sharpening stone with diamond abrasive. (Yep, have done it). The cost is especially excessive to me when the same benefit can be had by flattening the sharpening stone with a diamond plate. (Yep, have done it). This is one of those things that is really so simple there's no reason not to do it yourself - unless you're so busy that you just don't have any free time.
    Yea, not gonna disagree that the price is high and the process of cutting the stone is dead simple. I wouldn't doubt you could do it for a profit sub-$100/pair if you had a good process.

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    Quote Originally Posted by dgfoster View Post
    Hahn,

    Thanks for posting the video link to Robin’s work. He has to be one of the most meticulous craftsman I am aware of. Those stone look to be very useful and interesting. I can see pulling out a lot of what I think are beautifully finished surfaces and trying them with the stones only to be disillusioned. Slicking those surfaces down with ground stones would become addictive.

    Denis
    Too true- my Bridgeport table and vise mounting places were about as expected but found some horrors on my presumed clean and smooth 1-2-3 blocks. Got sidetracked painting the shop floor but will work my way thru all the stuff thats supposed to be smooth. I wonder what I'll find on some of the toolholders....

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    Hmm, considering grinding a 2"x6" stone flat on one side would take me about 15 seconds of machine time, if there is a market that could be something worth looking into. It would be way easier than making a switchplate out of the stone and they sell for more.

    What sizes, configurations, and grits would be popular?

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    It is worth noting that Rob Renzetti shows in detail exactly how he grinds his flat rectangular stones and how he has added a little kink to the grind to improve their performance. All that information is toward the end of the video. The fact that the OP's stones are prism-shaped would make holding them for grinding a bit more challenging. How would you hold them? Remember they come from the factory all surfaces far from flat so that a simple pass off the top, flip and a pass off the bottom is not going to cut it so to speak. I am wondering how these stones could be accurately machined in under one minute as one poster suggested.

    Denis

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    Quote Originally Posted by Richard King View Post
    Lance and Spencer sent me a set to test. They help after you get 20 PPI on a straight-edge as they stone the high spots down to the same plane. Prior to 20 PPI the regular unground stone works just fine. The ground stones get so smooth and they don't cut as well. The tapered stones I hand out in the classes are bent, some are high in the middle as much as .010". I buy them from MSC ( see below) I suggest you hinge the stone your using so you know if they are flat. Pictures are the stones I use. dsc01892.jpgdsc01891.jpgdsc01887.jpg
    richard, what do you think, are "precision ground stones" just another internet hype? i see no sense behind them:

    1. nothing comes out flat from a grinder. thats why you scrape. i have yet to see any quantitative indication on their flatness.
    2. for lowering high spots flatness is not needed. even sandpaper on a sanding block will do it. a piece of conditioned file will do it.
    3. the large size of the stones will hinder localized work. you use that size of slipstone for a reason. i use smaller ones.
    4. keeping the stones flat and clean is a lot of work.
    5. rubbing two of them together wont keep them flat.
    6. you cant correct geometry with them, they are too small. (if they had the size and precision of a surface plate, they might work.)
    7. if for some reason you want to use a large flat tool, a quality file is a much better choice (as i mentioned previously).
    8. for stoning smaller parts like 1-2-3 blocks they are too clumsy and regular stones work well.
    9. as has been mentioned, they are useless on a convex surface. they are useless on a concave surface as well. they will not take away the
    "low" high-spots.
    10. if you are trying to get something flat you dont get there by using a tool of lesser precision.

    i mean, you and others have been doing without them just fine, right?

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    dian, I love Valorbe files, nearly the equal of Grobet, and a better value (or at least used to be), but a file is relatively a mountain range, flatness wise.

    a precision ground stone is the "poor man's lapping plate" (unless you buy them from the OP, then you will end up a poor man) and a stepping stone (pun not intended) to a flat surface. would you grab a file and have a go at the ways of your machines? (maybe you would )

    the problem with them is they dont stay "precision" for long as you use them.

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    Quote Originally Posted by DavidScott View Post
    Hmm, considering grinding a 2"x6" stone flat on one side would take me about 15 seconds of machine time, if there is a market that could be something worth looking into. It would be way easier than making a switchplate out of the stone and they sell for more.

    What sizes, configurations, and grits would be popular?
    I've only used the Norton IB6 stones. I did order a bunch of cheap stones to compare but never got around to grinding them.

    Yea, the grinding ops are pretty quick. I think I was about 5 min/side but at least half that is attributable to my inefficiencies on the machine.


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