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  1. #21
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    a flat file if it is reasonably sharp, will still cut material of a flat work piece, because the contact area of the teeth of the file is small and can be overcome with hand pressure

    the whole idea behind the flat stones is you grind flats on the exposed grains, flats that are in one plane, and that creates a surface with a lot of contact area when pressed against another reasonably flat surface, if there are any small imperfections on the work piece surface, you will be able to apply enough of pressure to cut that raised ridge, but once it is near the plane of the surrounding are - the hand pressure will be too little to make the stone take a cut - that is all there is to it, coarse grain stones are better for this, if I remember correctly, Robin even suggests using coarse grain stones for this application

    and when used on a tool holder taper for instance, it is all about the contact area, which now is a line instead of a plane, so obviously you will apply less pressure in order not to cut any material on said line, but if there are dings with raised material around them, then it will take very little hand pressure to make the stone cut them, and again - the cutting action will stop one the stone makes contact on full length of the contact line

    * flat stones may not produce desired results when used by gorillas!

    edit: and these flat stones are nothing like lapping plates, lapping plates are just flat surfaces with sharp abrasive on them, so they will still cut another flat surface and take off material, but in order to do this, reasonable amount of pressure needs to be applied, if you have lapped anything flat, you'll know this already, but flat stone flats on the grains essentially prevent any cutting once the work piece is also flat

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  3. #22
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    my point really is, that you dont need anything especially flat to take off the high points.

    btw, my 16" straight cut valorbe file is flat to 5µ. it even hinges right. if you use it right it will do nothing to a flat surface.

    but back to the stones. apparently the prevailing assumption is that a diamond wheel will cut the grains and dull the stone. but it can as well break the grains out of the bond exposing fresh ones, depending on many variables of the grinding process. so its not just like grab a stone and take it to the grinder.

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    Well described jz79, very clearly summed up.

    I will point out a little contradiction in the edit though, a lap is nothing like a PG stone, but you have to put some pressure on it to work, just like a stone?
    actually I do get the difference, I understand the stone has a different role than a lap, I was partly making a joke there, also making an “extreme case” example.
    Stone is for touch up, lapping is a completely different process.

    Just to stir the pot tho, to get a surface plate to AA grade, do you stone it or lap it?
    Stay safe and be well cheers!

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    I now read what I wrote and yes, there is a slight "contradiction"

    Regarding the pressure and lapping, because there are a lot of tiny sharp edges on the lap, you need to overcome the "hardness" of the work piece multiplied by the number of cutting edges (diamond grains) to make then cut the work piece, and now think how much pressure you'd need to exert on the stone to push "soft work piece" into the recesses between the ground flat grains in order to make the cut - essentially the action is the same, but the difference in force required would be different by orders of magnitude, that is if the work piece is something harder than cheese, and that if we assume the stone is absolutely rigid, and they are not, so we could go on and on in this who was first chicken or the egg discussion

    and I'd use a lapping plate to grind a granite surface plate and bring it to spec, but if it was a cast iron marking plate, and I accidentally dropped something on it and made ding with raised edges, I'd grab a surface ground flat stone and knock the burr off to almost unmeasurable height above the rest of the plate and continue with my work :P

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  7. #25
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    I have known about precision ground stones for years. My Dad rebuilt machines at Professional Instruments in the 1950' and 60 when I was a kid. I taught a scraping class at Professional Instruments in the 1990's we did not use Ground stones when de-burring the scraped ways. Inside Professional Instruments grinding department they used the ground stones to flatten the mag chucks on their Okomota surface grinders. They stoned the table tops of their Jig Bores and VMC's. To remove or burnish over any small burrs, not to remove a ton of material.

    Many of the new to scraping hobbyists have picked up on the Robin show and look for short cuts to get a flat surface when scraping. As I said Lance B and Spencer Webb sent a set of their stones to test during my classes. I tried them and as I said they are useless when rough scraping because they are so smooth and they don't remove the bigger burrs. Before I started to use the tapered stones I used a dull file for the most part.

    I also had my students test the ground stones. Like I said after we got the practice plates flat to 20 PPI they would help flatten the super high spots. I personally would not need them as I have scraped for 50+ years with out them.

    I know this will tick off some of my students by saying this. I also don't think Robin is as good a scraper as many thinks he is (and others). I met a Journeyman scraper who apprenticed at Pratt & Whitney who was taught the Moore method. It was not the same way Robin does it. The hand scraper does not leave the surface as he moved forward not like Robins push and lift. He shows the his Moore scraping technique on a piece of aluminum and when he measures the level bottom with a electronic indicator, to me it shows flatness but the scraping is not deep enough. A good scrape job needs to be a minimum of .0002" to a maximum of .001" deep on ways and precision levels, so they last longer.

    If you pull or Moore hook scrape you don't generate as many burrs as you do by push hand and Biax scraping that leaves a burr at the front of the stroke cut. We need a file or medium grit stone to cut the burr off fast. I say in my classes " stoning is also a lost art". I don't recall any professional scraper ever using a ground stone. They are popular now in my opinion because of Robins You Tube show. The new to scraping hobbyists use them as a short cut to precision. But are fooled.

    In Austria, Stefan and Franz Luftinger the pro's (their company is Maschratur og. who are taking over the scraping classes in Europe introduced me to a German made ground stone that was sharp and it worked 100% better then these USA ground stones. They cut the Biax scraper burr off good. I will attach pictures. I did some research and could not find them in the USA. They also were cheap. One of you young entrepreneur figure out a way to sell them in the USA.

    Pic's L to R. The German factory ground stones. They have a flat and a tapered model, a straight edge Franz scraped with a Biax Power Scraper. 50+ PPI and Franz, yours truely, Stefan and Fillip BIAX Sales Manager the day I certified the brothers to teach my classes in Europe.
    Attached Thumbnails Attached Thumbnails 20171201_101453.jpg   20171201_101415.jpg   20171201_101438.jpg   20191016_140308.jpg   20191022_175607.jpg  

    Last edited by Richard King; 05-09-2020 at 11:47 AM.

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    Here is the Moore Method that I was shown by the Pratt trained guy. I was taught to push and lift. The scraping starts around 2 min mark... Also see how they use 3 points. Real Pro's. He stones it and the stone does not look like a ground stone. Also he hinges the part...
    YouTube

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  10. #27
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    I always thought of ground stones being for deburing ground work, that’s all
    The power of YouTube influencing what people want or need, well at least what they think they need

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    the tyrolit stones are i believe the most comonly used over here. i have a couple of them somewhere. but i like smaler stones.

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    I've never thought of the precision ground stones for use in scraping. And maybe I missed some videos but I can't remember anyone claiming to use them for that.

    Doesn't seem like a big deal in scraping if you use a regular stone fas you're in the process of altering the surface anyway and you're not trying to preserve an already ground flat surface.

    What I understood the purposes of precision ground stones where basically to remove burrs from precision flat surfaces, such as ground surfaces like machine tapers, without affecting the geometry of the surface otherwise.

    The main appeal of the stones as I see it is helping to maintain long term dimensional integrity of machine tables. Use this to remove burrs from your milling table instead of a regular stone and you will not dish it out over the years.

    You can also surface grind a file and make some flats on the surface btw. I use one to deburr various things as I don't have a stone.

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    How do I get I touch with Lance Baltzley to purchase his flat stones.

    Thanks
    Frank

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  15. #32
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    Lance and I are down in Florida --- send me a message and I'll pass on your info to him.

    He is attending the Santa Rosa Beach Florida Scraping class I start teaching tomorrow. He brought over his Rockford planer that we will be rebuilding as a project for the class to see. 651-338-8141 or [email protected]

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    Quote Originally Posted by Richard King View Post
    Lance and I are down in Florida --- send me a message and I'll pass on your info to him.

    He is attending the Santa Rosa Beach Florida Scraping class I start teaching tomorrow. He brought over his Rockford planer that we will be rebuilding as a project for the class to see. 651-338-8141 or [email protected]
    Ok thanks for the information someone posted his site for the stones.

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    I am grinding abrasive stones and at less than 100/pair for two sides can make a fair profit.The beveled stones take a bit longer but still not that much time. I use Tyroilt and natural Pyerrenies stones rather than Norton which are generally over priced and no better quality. I run straight grinding oil on my rebuilt Mikromat and am happy with the results. Shipping to the states is the same as anywhere outside of France so that isn't a big deal. (16 euros for two stones) and in the US you don't generally get taxed on import like over here.
    Luke


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