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I scraped a boudler into a master square, here's my report

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  • Jammer Six
    replied
    How does the 3 plate method generate a right angle? Build three squares at once?

    P.S. People who think there are no stupid questions haven't met my apprentice.
    Last edited by Jammer Six; 05-06-2022, 09:09 PM.

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  • Paul Alciatore
    replied
    I am glad you posted this. I have definitely learned from it.

    This is a topic that is not often discussed. And real world experience with scraping stone is very limited. I would have thought it was not practical. So I would encourage you to write an article and submit it to George at Village Press. He is both our moderator and the editor for their three machinist oriented magazines. He is always looking for articles and I bet this one would be immediately placed in the queue for publication.



    Originally posted by mtraven View Post

    thanks, I'm glad. For years I've lurked around here in the shadows & benefited from everyone's experience. Never really felt like I had anything to contribute, now I do. just trying to pay it forward.

    plus, ya'll can understand the value of something like this. Try explaining to a friend how accurate 0.0001" is & why you need it...i did, it was disappointing to say the least.

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  • Paul Alciatore
    replied
    There are no stupid questions. And sometimes when a very basic question is asked again, a new understanding can be the result.

    For the vast majority of the methods discussed here and elsewhere, YES that is true.

    BUT those larger and flatter surfaces must be produced somehow. And that "somehow" is the three plate method; well it is at least one of the "somehows". The three plate method does not require any additional or preexisting reference surfaces. It generates surfaces to whatever level of accuracy the maker wishes. And it also provides that craftsman with a pretty good means of testing just how good those three surfaces are.

    Now there are companies who make things like surface plates and straight edges and granite squares. And those companies will have their own methods for producing and measuring those surfaces and edges. But historically, in the end, it all goes back to the three plate method which was for centuries the basic method for generating a flat surface.

    Flatness can also be measured by optical methods. One optical instrument used is the autocollimator. But that is a whole 'nother subject.



    Originally posted by Jammer Six View Post
    After watching and reading about this, a stupid question: when you start, you have to have a reference surface that is both larger than your largest surface and flatter than your intended standard, are these correct?

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  • Jammer Six
    replied
    After watching and reading about this, a stupid question: when you start, you have to have a reference surface that is both larger than your largest surface and flatter than your intended standard, are these correct?

    Leave a comment:


  • rmcphearson
    replied
    My hat is off to you sir for completing this project!

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  • mtraven
    replied
    as BC said, granite is granite. As far as I can tell, the rock I picked was a pretty hard granite with a very fine structure to it. I don't have the ability to look at the makeup of the rock, quartz content for example, so thats all I can tell you. I read a little about stone selection in doing this project, turns out not even all granite tables are actually granite, often they are gabbro.

    Originally posted by JoeLee View Post
    I found a piece of counter top, it's about 1" thick or so, polished on one side. I would think that would be thick enough for a small square or triangle.
    JL............
    perhaps, really depends on how long you want to make it.


    re: quartz

    quartz countertops are actually quartzite--an engineered (man made) stone. 90% quartz, 10% epoxy. the epoxy would worry me for stability, unless a special low/no thermal E epoxy is used..which I doubt. The reason higher quartz content is desirable is, its hard & good for durability. But as with most hard things, strength is sacrificed. **generally speaking** pink granite has more quartz than black. Because of that, pink/white surface plates are thicker to make up for that difference. So with quartzite, you might run into problems like that, circumvented by a thicker table if ya like ...but there is still the epoxy that might change over time, not to mention may create problems when lapping being so much softer than the quartz.

    and I'll just mention, the durability concern is much more a problem for job shops, using their plates on a daily basis. as a home shop guy, I really doubt that block will wear in my lifetime. and if it does, I'll just re lap it.



    that being said, I have worked with a bit of basalt in the past. It seems like a good candidate, very hard, very fine grain structure...yet I've never seen a surface plate made from it (its got a characteristic green hue to it). I wonder why that is? Maybe its grain structure is too small do to its rapid cooling (basalt is a volcanic rock, granite is igneous). Everything I read says basalt is softer than granite, though my diamond saw says differently.


    edit: from the wiki on gabbro: "Slow-cooling, coarse-grained gabbro is chemically equivalent to rapid-cooling, fine-grained basalt"


    so I think it is, as I suspected, a matter of too small a grain structure.
    Last edited by mtraven; 05-03-2022, 03:16 PM.

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  • mixdenny
    replied
    Darn. I had a beautiful pink granite rock that split in half during construction. I kept it on display for years. I finally tossed it in the woods next to my house, I wonder if I could find it.

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  • BCRider
    replied
    But...... granite IS a rock ! ! ! To be fair it does depend on what sort of rock mtraven stated with. So MT, do you know the type of rock that you have there?

    A friend of mine is into stone counter tops but not that low class granite stuff. She's keen on full on quartz for a bunch of reasons. I wonder how quartz would be as a plate, square or straight edge?

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  • JoeLee
    replied
    Originally posted by mtraven View Post

    thanks! I actually started with a 10# sledge--there was a really obvious fault running through the rock & it need to come off---plus I REALLY didn't want it to break late in the process, figured slapping it around with a sledge might help show any defects. Plus its great stress relief (me & the rock)




    were you thinking it'd be better because of the type of granite? or because is already somewhat flat and more or less parallel?

    if your referring to the master square, its ~3 x2.5 x5.5", so counter top granite wouldn't have been thick enough. Plus I had that blank roughed out to within about 80 thou after just a few hours of cutting, it was 30 hours to finish it. so starting with nice blank, would be nice, but getting to that point is the easy part.

    That being said, part of the reason I took this on was, I have a nice granite drop from my sink that I intend to make a few edges like you described. This little block was a good learning experience(and proof of concept) gearing up for others. Though for the long edge I want to make, I'll be taking ~ 6" rip & using it on edge, more like a camel back edge. I dont really have need for a 45(i dont think?) but a 30-60-90 triangle or prism is certainly in my future. Does present some challenges in measurement that I not yet sure out to handle, like testing to make sure its exactly 60. Probably need a sine bar & gauge blocks to check that properly, I have neither. I think the 30-60 prism would be much easier, as you have 2 parallel edges.
    I was thinking that granite would be a better choice because of the quartz content, how ever much that would be in a black granite counter top. I think that a rock is just too soft and more fragile than granite.
    I found a piece of counter top, it's about 1" thick or so, polished on one side. I would think that would be thick enough for a small square or triangle.

    JL............

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  • mtraven
    replied
    Originally posted by boslab View Post
    I am envious of your new pet rock, it is the straightest rock I’ve seen, congratulations on an amazing bit of stonemasonary, I’m sorry to say I straighten bits of rock with a bolster and 3lb club hammer, so tenths are literally 1/10”! Well done ( you could make a really accurate pyramid)
    mark
    thanks! I actually started with a 10# sledge--there was a really obvious fault running through the rock & it need to come off---plus I REALLY didn't want it to break late in the process, figured slapping it around with a sledge might help show any defects. Plus its great stress relief (me & the rock)


    Originally posted by JoeLee View Post
    I applaud your efforts but wouldn't a piece of granite counter top be a more suitable material ? I had thought of making a 45 deg. and a 30,60,90 deg. square from one. The thickness was about right. Cutting it would be no problem but making it true would be. I'll be waiting on your results.
    JL.................
    were you thinking it'd be better because of the type of granite? or because is already somewhat flat and more or less parallel?

    if your referring to the master square, its ~3 x2.5 x5.5", so counter top granite wouldn't have been thick enough. Plus I had that blank roughed out to within about 80 thou after just a few hours of cutting, it was 30 hours to finish it. so starting with nice blank, would be nice, but getting to that point is the easy part.

    That being said, part of the reason I took this on was, I have a nice granite drop from my sink that I intend to make a few edges like you described. This little block was a good learning experience(and proof of concept) gearing up for others. Though for the long edge I want to make, I'll be taking ~ 6" rip & using it on edge, more like a camel back edge. I dont really have need for a 45(i dont think?) but a 30-60-90 triangle or prism is certainly in my future. Does present some challenges in measurement that I not yet sure out to handle, like testing to make sure its exactly 60. Probably need a sine bar & gauge blocks to check that properly, I have neither. I think the 30-60 prism would be much easier, as you have 2 parallel edges.

    Leave a comment:


  • JoeLee
    replied
    I applaud your efforts but wouldn't a piece of granite counter top be a more suitable material ? I had thought of making a 45 deg. and a 30,60,90 deg. square from one. The thickness was about right. Cutting it would be no problem but making it true would be. I'll be waiting on your results.

    Anyway............ Fred would be proud of you.

    Click image for larger version

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    JL.................

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  • boslab
    replied
    I am envious of your new pet rock, it is the straightest rock I’ve seen, congratulations on an amazing bit of stonemasonary, I’m sorry to say I straighten bits of rock with a bolster and 3lb club hammer, so tenths are literally 1/10”! Well done ( you could make a really accurate pyramid)
    mark

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  • BCRider
    replied
    I recall Tom Lipton doing a set of plates and showing the movements. So I did a YT search with the keywords "flat three plate method" and got Tom's video along with some others. I didn't watch the others but I suspect they'll deal with the proper methods for how the plate are worked and how often they move around.

    For flat edges such as lapping and proving the edges the method there was to pin the parts together so they are locked and then to set them slightly raised and use a brass or aluminium cylinder as the lapping tool. Rotating it so it wears evenly while lightly touching up the edges of the steel straight edges or squares. This is the last part of course. The initial work could be done using the mill... And with squares given a bit of a kick if your mill is like mine and is out of square by the amount I found it to be....

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  • mtraven
    replied
    paul-- thanks for the reality check on making lenses, I needed that. I was thinking that lens would be hundreds (i have no frame of reference). and its not the only precision optical component in an autocollimator.
    thanks for opening my eyes to surplus optics. there's a great surplus store near me that I've been going to for 20+ years, they have a whole optics isle that I haven't ever looked real closely. you got me thinking about where else I could get parts, pretty sure rifle sites use collimation. and dont DLP tv's have some precision mirrors in them? I have a few of those laying around, they might be handy on the sled.


    BC-- i've never actually worked through the 3 plate, but I have read many accounts of it--with small variances. but all of them involve exact (usually 90deg) rotation between rubbings, parallel is fine, but perpendicular is gonna destroy both surfaces if the L:W is way out of whack. That being said, I -think- it should be possible to prove 3 edges against each other, I just don't think that can be the technique for actually removing material.

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  • BCRider
    replied
    Guy Lautard in one of his volumes of "The Machinist's Bedside Reader" books detailed a procedure for making and lapping a pair of squares to a very high degree of squareness. It involved doubling the errors by making TWO pinned together squares and using a lapping button to lap the edges. A little lapping then offer the squares to each other along a known straight edge against a light table (or handy window with some paper as a diffuser) to see any gaps. The same could be done with two long straight edges. Precision pins with a light press fit?

    I also wonder about the idea that if a set of three surfaces can make a set of three flat plates if given enough time then why can't three thin edges do the same? I'm not sure how that would work with granite since even a granite straight edge in practical terms is more a long and skinny surface plate than it is a true straight edge. Or would a "V" edge lapped to a narrow flat qualify?

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