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Hard to machine alloys myths

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  • Hard to machine alloys myths

    I got sections of "brass" bars from a friendly scrap, where they allow me to throw in any scrap and get some odd bar or something what is of use for me but only a "metal value" for them.
    They need 1.5 times as much of the same metal as they give or something alike.

    I brought said bars home, they were proudly placed on the shelf and some item were made on occasional basis.
    While working with it on the lathe, I have found that it can be turned (or threaded...) beautifuly, albeit chippings were not exactly like from ordinary brass.
    I had a look at these bars again, and the brass was looking somewhat crap.
    Of course it had some copper like color, albeit rather faint, if you compare it with "proper" brass.
    It was sort of "too silverish".
    I thought, it is crap, "undercoppered" brass and closed the case.
    Today I have decided to make a housing for strong neodymium magnets out of it and up to my surprise I have found that alloy is somewhat magnetic.
    It was attracting powerful neodymium magnet about as strong as steel would attract crap ferrite magnet of the same size and used for example to keep kitchen cupboards locked.

    Now, *magnetic brass* is a nonsense, no such animal exist.
    So I have started to suspect that I might be dealing with *monel 400*, an alloy of about 67% Ni, rest Cu (grades of monel with significantly lower Ni content are not magnetic).
    Now monel is classes between so called super alloys due to a very sought after mechanical and chemical properties.
    I have decided to investigate matters further, dissolved sample in dil. nitric acid and run tests on Cu and Ni (easy enough to do at home for a chemist btw).
    Surely both were found.

    Now, monel is quite an expensive stuff and I brought home about 25 kg of it in different bar diameters *for next to nothing*.
    Plumbing waste, some brass turnings and some stainless scrap was traded in.

    But other interesting observations were also made:

    1. It turns beautifully and you can approach it *like brass*. HSS tools were used
    2. Surface finish ex knife is beautiful, without paying any particular care and attention.
    3. 1.5 inch bar was parted off on 3 1/2 inch lathe, without any jamming, whizzing and other unpleasantness.
    HSS 3/32 inch blade was used.
    4. It can be threaded with ordinary taps usually used for carbon steel.
    5. Overall impression is that carbon steel is a real s*it in terms of machinability, comparing to this alloy

    BTW, my tools are rather sharp.

    One should note that Monel is considered to be a very hard staff to work with between machinists.


    Now, this adds to many of my other observations regarding *hard to turn* materials:

    1. Titanium (Ti6Al4V) is between most pleasant materials to work with which exist.
    Turns and threads *fantastically* and a surface finish is absolutely superior, ex knife.
    As a bonus chippings can be burned with brilliant white flame and impress my wife

    2. It is not true that a stainless steel is a vicious material which work hardens and makes your life miserable, that provided that you don't attempt to turn or drill it with a blunt nail.
    Stainless turns brilliantly (304 type a bit better than 316) but about 2/3 of depth of cut is to be taken comparing to carbon steel.
    As a bonus, it gives vary good surface finish, even without much care and attention.
    Normal tooling can be used for threading and buying special stuff for stainless is a *waste of money*, at least if you don't try to run mass production.

    3. For all practical purpose work with other difficult to work with material (Monel) is not really more challenging than work with brass.

    4. Hastelloy, at least Hastelloy B3 turns comparably to stainless.

    5. Cold worked stainless is harder to work with but gives good results with some patience.
    In any case only small diameters are handled, but contrary to many claims carbide tooling is rarely, if ever, essential.

    6. So called *mild steel*, particularly *bright drawn mild steel* is the ****tiest material in everyday work.
    Particular troubles are with securing good surface finish
    These observations do not apply to F/C steel.

    So I wonder from where all this mythology about hard to turn materials is coming?
    Why machinists hate stainless?
    Because they cant be bothered to sharpen their tools when needed?
    Last edited by Martin0001; 10-14-2013, 04:50 PM.

  • #2
    So I wonder from where all this mythology about hard to turn materials is coming?

    When you encounter some stainless work hardening you will wonder no more. My first bad experienced involved a mister that became an automatic quencher.
    Byron Boucher
    Burnet, TX

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    • #3
      But I am invariably finding out that it does not work harden, for as long as you use sharp tools.
      I got it to work harden, but only deliberately and even then not all is lost.
      Well sharpened HSS will deal with it.
      On very rare occasion carbide is needed but you will only get there if something horribly wrong was done in initial work.
      I think, major problem steams from general laziness and assumptions that 18 inch lathe with 25 horses on journal will turn even with a blunt nail in the toolpost because it is strong enough.

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      • #4
        Mystery metal really isn't worth it. While it does lead to some interestig experiences mystery metal can be disastrous if used in the wrong place. So use that stuff for practice and sacrifical set-up apparatus only and keep it segregated from known materials. If you have to make a real shaft, bushing, or fastener make them from materilsa you can positively identify.

        I know many work on a tight budget making free materials attractive. But if safety, durability, etc are on the line at least think of using suitable, properly identified materials. Various informal shop tests can go a long ways towards material ID. Spark test, acid test, file test (taste the filings; comparing known to unknown by taste really is possible,) hardening test, etc. All require minimum equipment and while subjective for the most part a keen eyed observer can make some shrewd guesses. You cannot apply these tests after a quick Google. You have to cultivate your senses and acquire a selection of known materials to use as samples for comparison.

        As for material tricky to machine, try welded Stellite seats 11" into a steam valve having an opening less than 3" dia. Bottom blow valves. I did pallets of them and I hated every one. You worked by sonar, feeling your way listening for a touch. The stuff broke tools, work hardened like crazy, you you had to get a 44 1/2 degree seat angle and a round intersection al with a fine tool finish. It took a bottle of Tums for every pallet load.
        Last edited by Forrest Addy; 10-14-2013, 06:24 PM.

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        • #5
          Originally posted by Forrest Addy View Post
          taste the filings; comparing known to unknown by taste really is possible
          I donno man, does it taste more like ledloy or beryllium copper? That would not be my first choice.

          A "hackerspace" "makerspace" type place could fundraise by buying one of those magic four figure xray neutron spectrometer doohickeys and let the general public blast random metal for $1 a pop or something like that on open days. That doesn't tell you anything about heat treat/temper (or does it?) but at least it tells you composition. Like most people I have some mystery metal I'd like identified. Probably nothing exotic, but it would be interesting to know what it is. I would imagine they have a similar fundraising opportunity for screwing around with thermal IR cameras and probably borescopes.

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          • #6
            As per "mystery metals", my primary profession is chemistry, I have friends in labs, can get access to analytical equipment for free to make an odd check and certain initial analysis can do at home.
            For this one I am pretty convinced, it is Monel, but if I need to make for example valves for an autoclave carrying compressed hydrogen fluoride (it is legitimate application of Monel), I will have it checked again.
            Materials like this are relatively easily to identify (Monel is about the only magnetic copper alloy with copper as one of main elements, (and heating it to 50*C or so will make it nonmagnetic) but task becomes very hard or next to impossible, if you try to distinguish between various alloyed steels.
            Few hundreds of types, each one with different heat treatment regimen etc.
            I do not want to find myself there.

            Even materials like brass or bronze have many dozens of subcategories each... and files are no longer made of straight high carbon steel... or some of them are and some other are not.

            Yes, unknown material from a scrap is not a very good idea, if something critical is to be made of it, no argument here.

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            • #7
              I believe some brasses and bronzes can have a faint magnetic signature.
              A compass manufacturer I talked to at the London Boat Show years ago told me that his firm (Sestrel) tested every bit of brass they used, to guard against any stray magnetic effects in their compasses (and they were world leaders in the magnetic compass business).
              And I think manganese bronze (which isn't a bronze at all, but strictly speaking a brass) can be slightly magnetic, too.

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              • #8
                It is testing positive for copper and nickel.
                Will give a sample to check it properly, just out of plain interest.
                Will cost me a bottle of wine...

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                • #9
                  Sounds like copper-iron: A.K.A ASTM C194. ~2.5% iron, the balance copper.

                  Back in the 70's/80's, it was used for stamped IC connectors:

                  http://www.fiskalloy.com/product/c194/
                  "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                  • #10
                    Copper Iron of composition as you describe should be red.
                    My stuff looks at first glance more like stainless.
                    Upon close inspection it shows a week copper like discoloration, much weaker than normal brass.
                    I have positively identified copper and nickel in it.
                    I was not testing for manganese or iron.
                    Will get chemical analysis in friendly lab but that will take some time.

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                    • #11
                      Originally posted by Martin0001 View Post
                      Will get chemical analysis in friendly lab but that will take some time.
                      Just about every scrap yard and gold/silver merchant has an XRF gun these days. Ask nicely and they'll zap it for free
                      "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                      • #12
                        I noticed INCONEL wasn't mentioned, for good reason.
                        Probably the worst crap I've had the displeasure to machine.
                        I had the unfortunate job of drilling and tapping 3/8 NPT holes alongside 10-32 holes in 12 plates of INCONEL.
                        Torn threads in the NPT holes, and broken taps in the 10-32's.
                        Horrible stuff.

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                        • #13
                          AMPCO bronze ( trade name ) contains iron and is slightly magnetic. It comes in various grades. AMPCO 18 is a popular grade and cuts
                          fairly well. Other grades not so much. A good magnet will identify these bronze types , but not the grade. Some of these bronzes are very difficult to work with.
                          Toolznthings

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                          • #14
                            Ampco 45 maybe ?
                            Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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                            • #15
                              Originally posted by TOOLZNTHINGS View Post
                              AMPCO bronze ( trade name ) contains iron and is slightly magnetic. It comes in various grades. AMPCO 18 is a popular grade and cuts
                              fairly well. Other grades not so much. A good magnet will identify these bronze types , but not the grade. Some of these bronzes are very difficult to work with.
                              Arghhhh.
                              You beat me to it guys!
                              Ampco surely fits that description.
                              They market bronse and copper super alloys under the same name. Which makes them a little confusing.
                              Softer ones machine very close to mild steel.
                              Yes those alloys can go upwards of 300 HB, whoch is not fun anymore.
                              It has superior heat transfer abilityes and is often used for cooling rods and mold inserts.

                              Btw turni g is about the easyest things you could do to work hardenable materials.
                              It is easy to keep the proper chipload and tools are sturdy.
                              In milling you often have to compromise and many people compromise on feedrate which is wrong.
                              Last edited by Zero_Divide; 10-15-2013, 12:49 AM.
                              FSWizard - Free Online Speed and Feed Calculator

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