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  • non destructive testing of materials

    so you have a peice of something and want to know if the saw will cut it.

    by bouncing bearing balls on the surface (perhaps in a tube), can you determine by comparison, how hard the stuff is?
    Last edited by dian; 12-15-2013, 11:15 AM.

  • #2
    Chuck it in the saw and try cutting? Otherwise the only option is indeed hardness measurement, but it doesn't tell you how miserable the material might be to cut.
    Amount of experience is in direct proportion to the value of broken equipment.

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    • #3
      Try a hacksaw first. Those blades are cheap and easy to replace if needed.

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      • #4
        Spark it, you can determine carbon content, low carbon at least not hard, may still be miserable to cut tho. Otherwise, I'm in the hacksaw camp, maybe a file to check for hardness. Bob.

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        • #5
          I read dian's question less as a practical inquiry and more as a technical curiosity. Does hardness affect the height of rebound from a dropped ball bearing? I don't really know the engineering explanation for that, but I will take a guess and say, "yes." My understanding is that is how these simple, portable hardness testers work: Rebound THT-6. Correct?
          Last edited by Arthur.Marks; 12-14-2013, 04:04 PM.

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          • #6
            That looks somewhat like the glaucoma test tool that is used for eye exams, although I think now they use compressed air.
            http://en.wikipedia.org/wiki/Ocular_tonometry
            http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3641509/

            The rebound hardness test is discussed here:
            http://en.wikipedia.org/wiki/Leeb_rebound_hardness_test

            Has anyone tried one of these?
            http://www.ebay.com/itm/251328119508

            McMaster has various hardness tester tools, but are typically $100-$1000 or more.
            http://www.mcmaster.com/#hardness-testers/=pt5oqj

            Perhaps it would be possible to get some samples of metal tested at various degrees of hardness and use them to try to scratch the part to be tested. But that might be considered destructive if it is a critical surface.
            http://pauleschoen.com/pix/PM08_P76_P54.png
            Paul , P S Technology, Inc. and MrTibbs
            USA Maryland 21030

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            • #7
              Seems to me the easiest way is still to simply try to file it - at least that's what I was taught. If a file cuts the material so will a HSS cutter.

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              • #8
                Angle grinder with a ZIP wheel, doesn't matter how hard it is.
                The shortest distance between two points is a circle of infinite diameter.

                Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

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                • #9
                  How about Hardenss Testing Files?
                  http://www.hardnesstesters.com/Produ...ess-Files.aspx

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                  • #10
                    The bouncy ball test is the scloroscope, thinking shore, a scratch test with a piece if hss like a scriber will be enough to tell you if its sawable, or the old file test, i havent yet found any difficulty with that! I dont think the carbon content will make any difference, it depends on the heat treatment, if it is high carbon steel then anneal it, it would be unusual to be making something out of hardened steel.
                    There are cast irons that defy sawing as they are chill crystal encased, hard to get through pure Fe3C, cementite, that is as hard as a ferrous metal gets short of nitrided steel, even diamond files have a finite life against that stuff, it kills them by attrition, literally
                    Mark

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                    • #11
                      Just a note, but OP asked for non destructive testing, so filing, sawing and sparking is out. Basically leaving hardness testing and chemical sniffer analysis as the only options.
                      Amount of experience is in direct proportion to the value of broken equipment.

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                      • #12
                        Originally posted by DATo View Post
                        Seems to me the easiest way is still to simply try to file it - at least that's what I was taught. If a file cuts the material so will a HSS cutter.
                        x2

                        I file test everything I question on hardness. If the file digs in any bit the saw will cut it.
                        Andy

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                        • #13
                          Originally posted by Jaakko Fagerlund View Post
                          Just a note, but OP asked for non destructive testing, so filing, sawing and sparking is out. Basically leaving hardness testing and chemical sniffer analysis as the only options.


                          I don't find filing "destructive". There is always some spot on a part that can take one swipe with a file and not harm anything.
                          Andy

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                          • #14
                            I have got to ask (because it has been bugging me every time I see mention of it) if the material is harder than the file, does the file suffer any damage?

                            Good files seem to be increasingly hard to find and I don't want to damage the few half decent ones I own. The crappy files won't cut much of anything, so they are useless for testing hardness in my eyes.

                            So, are the files damaged or not?

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                            • #15
                              Originally posted by Mike Nash View Post
                              I have got to ask (because it has been bugging me every time I see mention of it) if the material is harder than the file, does the file suffer any damage?

                              Good files seem to be increasingly hard to find and I don't want to damage the few half decent ones I own. The crappy files won't cut much of anything, so they are useless for testing hardness in my eyes.

                              So, are the files damaged or not?
                              If the material is harder than the file, I don't see any way it could NOT be harmed. At lest the file teeth
                              that came in contact wiht the material.
                              ...lew...

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