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  • Shop “stoning”

    I commonly see folks “stoning” a surface when working on or with milling material to clean it up. Does this stone have a particular name? Are there recommendations as to size, shape, brand?

  • #2
    India is the best to use for this, as they don't shed much grit. Carborundum or silicon carbide will. Make sure to get the stone flat first. You can do that by lapping it flat on a good quality diamond plate or surface grinding it with a diamond wheel. After that, when used you should basically "float" the hone over the surface with almost no pressure and feel for any high spots. If there are very large lumps and bumps, better to use a file first. This type of hone really only works well for very small upsets, scratches or nicks.


    • #3
      If you use a file, use a "burr file". A regular file or piece of file that has been flattened a bit on a sharpening stone so that it only cuts what sticks up.
      CNC machines only go through the motions


      • #4
        There are two types or styles or types of stoning; using a standard stone to remove any raised material from dings in something like a mill table and using precision ground, flat stones to improve the finish on almost any flat part.

        The standard stone method is a light pass with a standard stone to remove any raised material from a ding. The stone is a normal, abrasive stone but it must be relatively flat. Run of the mill stones from your local hardware are not that flat and should not be used. If a stone rocks when placed on a flat surface, do not use it because the two corners that are in constant contact will take more material off the surface than the rest of the face of the stone. Stones can be flattened by various methods: you can search the internet for this. And the stone used should be a relatively fine one as you are not trying to remove a lot of metal, just the unwanted high spots. I am speaking of high spots that are substantially larger than the ones below in my description of precision ground, flat stones.

        Other uses for standard stones would include the deburring of edges and, of course, sharpening knives and other tools.

        Then there are precision ground, flat stones. These are around five to ten times the cost of standard stones ($100 and up) and they are always sold in pairs. They have been ground flat by a diamond wheel, usually on a surface grinder which makes the overall surface very flat. The other thing about them is the grinding process does not remove whole abrasive grains. It cuts off the exposed tops of those grains leaving a flat surface on them. These flat surfaces are co-plainer on all of the abrasive grains on one face of the stone so nothing sticks up. This degree of flatness can not be achieved by other methods which flatten the stones by removing abrasive grains, exposing fresh grains with sharp peaks. Any small amount of material that precision ground, flat stones remove is cut by the edges of these flattened abrasive grains, not by the peaks because there are no peaks.

        Now, if you are familiar with the theory behind any cutting tools, any cutting edges, then you know that those cutting edges must have relief behind the cutting edge if it is going to penetrate (dig into) the material being cut. Lathe tools, milling cutters, saw blades, files, chisels, any tool that cuts has a relief angle behind the cutting edge and these tools remove material relatively quickly. And this includes the abrasive grains in any stone, sandpaper, etc. All of these have relief that allows them to cut deeper.

        But the abrasive particles in a precision ground, flat stone do not have this relief. Their faces behind the cutting edges are parallel to the overall surface and to each other. They simply can not dig in. They glide smoothly over an already flat surface, removing nothing. So what do they do? They remove any SMALL projections from a nominally flat surface: I am talking about tenths here. Any milling cutter, lathe tool, saw blade, etc. will leave some surface scratch pattern with hills and valleys. When a precision ground, flat stone is run over such a flat surface, it will only remove the very peaks of those hills and it will do that quickly at first but then, as the hills are reduced the removal process will slow down and even fairly heavy pressure will not remove much more material. The surface has been improved but very little material has been removed, usually only a few tenths. You would have to abuse them to the point of destroying their flat surface to remove even a single thousandth of an inch with them. And because they do not remove anything but protrusions, they are completely safe to use on precision surfaces. They are even safe to use on Jo blocks.

        I said that precision ground, flat stones are supplied in pairs. In order to function properly they must be flat and free from any protruding material which would hold the stone above the surface while scratching it. The proper way to use them is to wipe both stones in a pair with a clean rag and then rub them together a few times with light to moderate pressure. This causes each of them to remove any protruding material from the opposite stone, leaving both completely flat and ready for use. In doing this you will initially feel some resistance due to the cutting action. But after two or three strokes they will glide over each other with the feeling of a highly polished bearing surface or that of an air bearing. In other words, they show almost no resistance to the rubbing. This is done before every use to insure that the stones are ready for use. This is why they are always supplied in pairs: they are used to clean each other.

        Precision ground, flat stones should not be used where the removal of material is desired. This includes most tool sharpening and any surface that is not already nominally flat. I have used mine on things like 1-2-3 blocks, the edges of scales (rulers), the working surfaces of squares, etc. With care you can even use them on cylindrical surfaces, like shafts. I do not use them on my mill table because I know it is not nominally flat. It currently measures about +/-0.0015". If I scrape it or use some other method to improve the flatness of that table then I would use them on it. But not until then.

        Paul A.
        SE Texas

        And if you look REAL close at an analog signal,
        You will find that it has discrete steps.


        • #5
          I am a tad ignorant on such matters but my system is three cheap sharpening stones from the local big box store. I rub them against each other and use them in rotation to repair dings etc and to finish surfaces. I finish up with a oily rag over the workpiece.


          • #6
            Originally posted by mwill135 View Post
            I commonly see folks “stoning” a surface when working on or with milling material to clean it up. Does this stone have a particular name? Are there recommendations as to size, shape, brand?
            You seem to be talking about using the stone on the work items. The others are mostly referring to stoning (or burr filing) the machine surfaces to cut off any burrs. So which is it you are looking at doing?

            For simply deburring the work pieces during or after being machined I prefer a regular smooth cut file if that helps.
            Chilliwack BC, Canada


            • #7
              I currently own a series of Norton sharpening stone and a diamond lapping plate. I can just use those. I was thinking of the round(~4in) stone I see utilized by various machinest online.


              • #8
                Any hone flattened by a good quality, *actually flat* diamond plate will work just about the same as one ground flat by a diamond wheel. The diamond abrasive cuts the abrasive particles to a flat plateau either way. A 320 grit diamond plate does a pretty good job. I've used both styles for many years - I started flattening hones and using them that way long before it was the fad that it is these days. I think I flattened my first hone for use in the machine shop probably 25 years ago. Those types of hone work just fine whether on a mill table, workholding devices or the wokpieces themselves. They are for smoothing out small damage and/or evening out a work surface. They don't really remove much of anything. I'd far rather use a file or the mentioned burr file for anything larger than a scratch or very small ding.


                • #9
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                  • #10

                    Get a Blanchard Burr Buster.
                    Made specifically for stoning flat magnets ( or a table ).
                    If you are going to do it, you aught to look like you know
                    what you are doing. A blacksmith does not use a claw

                    "Everybody must get stones".

                    --Bob Dylan
                    Last edited by Doozer; 05-26-2022, 08:38 AM.


                    • #11
                      Once again a no-bull reply from Doozer.
                      Last edited by reggie_obe; 05-26-2022, 09:32 AM.


                      • #12
                        But the sad truth is that the cheap skates here
                        would rather use a flat rock they found in the creek
                        than pay for something to make their lives easy.
                        Disclaimer: Only be offended if this applies to you.



                        • #13
                          I'd get the "gold" burr buster like Reggie linked if you want to stone a precise surface - it's aluminum oxide rather than silicon carbide like the one Doozer depicted. Either way - flatten it!


                          • #14
                            I have a set of green and a set of orange.



                            • #15
                              Not used stones since leaving mold making. A 123 block and wet / dry paper wrapped around works for me. Some lite oil and you are good. Now you can go from 80- 900 grit. Arkansas stones were in every tool box years back.
                              Last edited by Fasturn; 05-26-2022, 10:07 PM.