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  • machining copper

    A mate of mine has asked me to help him with his jewelry platen. I have not seen it but I think it is a 200mm disk that is 6mm thick that runs on a mandrel. It does not run true and he wants me to face it on both sides to run a bit better. What can I expect when I machine this. Are there any tricks to machining copper. Should I use a kind of lubricant?
    Also this disc is charged with diamond paste for his lapping purposes. I wonder if this would dull the cutter Thanks

  • #2
    Plunger is the disc charged with diamond paste on both sides or just one?

    If its only one side then true that up with light cuts with a fairly sharp tip and a medium speed ,I did a seal base in copper about about 1/2 that diameter and it cleaned up nicely .

    The diamond paste will cause problems until you get under it so you may need to have it mounted securely and try a cut that will be under the depth of the charged area.
    Michael

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    • #3
      Sharp HSS cutter with a HUGE hook shape ground on top of it. And (flood) coolant applied to the center of the disc, it spreads from there nicely around the whole disc area to provide cooling and lubrication.
      Amount of experience is in direct proportion to the value of broken equipment.

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      • #4
        Use lots of relief and clearance on your tool, much like wood. I use use WD-40 as a cutting/tapping fluid on all non-ferrous metals.

        Tom
        Tom's Techniques

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        • #5
          If you start getting oscillations in the cut, slow down to a snails pace to get the waviness out of the surface. Otherwise they just keep getting magnified with each cut.

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          • #6
            Believe it or not, one of the very best cutting fluids for pure copper is actually whole homogenized milk. If there is diamond paste in it even carbide tooling will wear fast. Try to get under it with the first pass.

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            • #7
              I have had the best results cutting copper with TapMagic for Aluminum. I have found it works great on all non ferrous metals like brass and bronze too. It's the best thing for aluminum, especially soft gummy alum.

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              • #8
                At 200mm and 6mm thick it will probably want to chatter like hell.Cutting some rings out of plywood or particle board and gluing them to the backside helps dampen the chatter.

                +1 for WD40 or Kerosene,either works well on Copper.
                I just need one more tool,just one!

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                • #9
                  Check out your local machine tool black market for some 111 trichloralethylene "aka" the old style Rapid Tap. Marvellous stuff on copper.
                  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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                  • #10
                    I wonder if it could be cold-worked back to true, like metal spinning.

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                    • #11
                      Now the very first thing you'll have to do, is make sure your health insurance is fully paid up and covers for what you are about to do.

                      Seriously, that stuff is like gum to work with, if you haven't got it captured extremely well, then it's going to try and escape, the tool tip will bite in and it's out and gone, if your in the way, whoops------.

                      Metal spinning might be the only way to push the diameter back into round, as you would use a tailstock to hold it in place, but to take a heavy cut across the face while trying to hold it in the jaws with only 6mm thickness, someone might be hospital bound very quickly.

                      If you do decide to have a go at it, then please video the procedure, as I for one, would like to see how quick your reaction time is.

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                      • #12
                        My mate brought three discs to be machined. Two of them were not charged with diamond paste. We tried the one charged with diamond paste first.I tried a piece of hss with lots of positive rake and honed real sharp and used plenty of soapy water. The bit disappeared in front of my eyes.No problem I just used a tungsten carbide bit.That disappeared too.I then changed lathes because my emco v13 doesnt deserve diamond dust all over it.We then sharpened a couple of brazed carbide bits on and I could feel the plate starting to lose its cutting ability. I then used a diamond wheel dresser to try and clean it up but that was also disappearing but you could see the disc was losing its grinding ability.I then pulled out a 9 inch diamond angle grinding blade I use for chasing walls that was put into retirement and used that. Eventually I managed to clean it up but what an exercise.I got some bad chatter but cleaned it up and then put it back on my emco on a mandrel and used a carbide tip designed for aluminum and it cleaned up quite nicely.
                        But I am battling for trueness. What I mean by this is that it cleans up nicely but if I remove the disc and put it back on the mandrel it has a run out of about 0.2mm.The other plates should be easier to machine because they are clean with no diamond paste and I am hoping if I machine them between centers they will be true. The slower speed helped on the outer extremities because if I went to fast it chattered real bad and got hot real fast
                        But this whole story got me thinking. Is this the same way they sharpen tungsten scrapers. Could one use cast iron on an old motor to make a tungsten carbide grinding tool as my green wheel I use for carbide has nothing on this diamond lapping wheel my mate uses to cut his gemstones with

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                        • #13
                          Sounds like the plate you worked on was work-hardened. You might want to anneal them before going any further.

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                          • #14
                            We used to anneal copper at the spinning company between stages... heat it to glowing orange-ish and slap it in water. Basically went from RING-hard to "thunk" soft.

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                            • #15
                              You don't have to go that hot for copper. You might get some sag. Dull red is hot enough and the water dunk just speeds handling. It doesn't help or hurt the anneal process.

                              I think you need some backing on the disk. If your out .008", it's moving. Try turning it against a dressed backing plate with an index on the bore of disk. I also wouldn't rule out that the mandrel isn't out of square or the bore of the disk is out.

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