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4-40 thread in copper- form or cut tap?

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  • 4-40 thread in copper- form or cut tap?

    Hey All,

    Got a project coming up that requires a bunch of 4-40 tapped holes in pure copper. I'm guessing form tap rather than cut tap? Never worked with copper before or tapped something that small.

    While I'm at it, anyone have experience machining macor (a supposedly machinable ceramic) or phenolic? I'm not expecting problems, but figured I'd ask anyway....

    Thanks!

    -aric.

  • #2
    I had to drill some 1/4" copper plate once and it was difficult.
    These guys told me to use milk as a lubricant which worked OK but I can't imagine trying to tap it 4-40.
    Maybe an insert?
    Mike

    My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

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    • #3
      I'll ask if there's anything we can do to make life easier (like threaded inserts), but I suspect it's a no-go as it's a mounting block for a heatsink in a high current superconducting transformer (or something like that... it's my brother's project and I'm fuzzy on the details) and the different metals would likely cause problems either electrically or physically (due to differing expansion) when the device is submersed in liquid nitrogen.

      In any event the piece is only 1/8" thick and copper's not horribly expensive (just checked McMaster for the macor and HOT DAMN!!!), so no that big a deal if the first try doesn't work.
      Last edited by adatesman; 03-01-2012, 05:25 PM.

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      • #4
        Tapping

        I use a blend of mineral spirits and a Mobil cutting oil with copper. Straight mineral spirits is OK

        The machinable ceramic. Use carbide and feed slow. It is dusty and the dust is abrasive. Cover up the ways.

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        • #5
          Drill the hole a little bigger than normal and use a forming tap. It's very, very, very gummy. And not in cute bear way. I had success with thick high sulfer threading oil, but it turned the copper black. Tap-eaze might be the way to go.

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          • #6
            I do as small as 2-56 with form taps in copper all the time, use the correct drill, use tap magic or some other lube meant for tapping and tap away, its really not that hard. You could also use milk I guess, or maybe if you have some whales around you could use some whale blubber, that stuff is supposed to be the bomb for tap lube

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            • #7
              I had a similar situation years ago, before getting into machining. A friend led me into first tapping a larger, thicker piece of metal to hold over the thin stuff to prevent what he called "blooming" of the hole (the thin sheet edges are lifted by the tap.) I was working brass, so the rest of the problems do not relate.

              Pops

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              • #8
                http://www.google.com.au/#pq=tapping...w=1920&bih=785

                http://www.google.com.au/#hl=en&rlz=...w=1920&bih=785

                If it were me I'd use a reversing tapping head in the drill or mill and use a straight flute or gun tap, but if the copper is likely to be or is work-hardened before or due to tapping I'd use a form tap and keep going (do not reverse during the forming operation).

                Use a lot of good tapping fluid and a low speed to allow the copper to "cold form". Higher speeds will not help.

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                • #9
                  What about the phenolic you say?

                  The've got you convered on the thread forming, sounds good to me. That said different alloys can be significantly different so you may want to check that out too. It may be far harder than you'd first expect when you hear "copper".

                  As for the phenolic....great stuff to work with I love it. What you want to be aware of is that there are several different grades with very different properties. There are two main strata though, the paper based and the cloth impregnated. For compression the paper based is OK but for tension you want the cloth type. BTW both types are like plywood in that they are layers of materal laid down together and bonded with resins. The both will delaminate with stress inflicted in the direction of the laminations. The cloth based is dramatically better but of course the cost of materials reflects that.

                  You shouldn't have too much trouble with the task.
                  Allans Rule: Anything worth doing is going to be a pain in the butt.

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                  • #10
                    Originally posted by Clevelander
                    The've got you convered on the thread forming, sounds good to me. That said different alloys can be significantly different so you may want to check that out too. It may be far harder than you'd first expect when you hear "copper".

                    As for the phenolic....great stuff to work with I love it. What you want to be aware of is that there are several different grades with very different properties. There are two main strata though, the paper based and the cloth impregnated. For compression the paper based is OK but for tension you want the cloth type. BTW both types are like plywood in that they are layers of materal laid down together and bonded with resins. The both will delaminate with stress inflicted in the direction of the laminations. The cloth based is dramatically better but of course the cost of materials reflects that.

                    You shouldn't have too much trouble with the task.
                    MACOR is not phenolic. Macor is a machinable ceramic.

                    When machining it, you always want to cut it where your tool is climb cutting and cutting clockwise on the part. The edges are very susceptible to chipping out. Make sure you use a sharp tool for the best cut. HSS works but carbide is better. As with any ceramic, it will dull your tool eventually. Any drilling or tapping, try to use a new tool if possible. For tapping, I always prefer a 2 flute gun tap for Macor to prevent loading up. Use a little oil on the tap.

                    And above all, Macor will create a very fine abrasive dust. Make sure you wipe all of the ways off good when done machining it. I try to cover as much area as I can with shop rags to prevent the dust from getting on the ways.

                    And most importantly....DO NOT breathe the dust. If you have a ShopVac, use it to keep the dust cleaned up while machining. Or use the ShopVac to clean up afterwards. Don't blow everything off with an airhose. And if possible, wear a dust mask for protection.
                    If it's not good enough for you, it's sure not good enough for anyone else.

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                    • #11
                      Bit of follow-up....

                      All the advice above was much appreciated and quite helpful, as I didn't run into a single snag today. Turned out the copper was the ultra-high-conductivity version and super-duper gummy, but otherwise wasn't bad to work with and the form tap was a piece of cake in it. The macor wasn't too bad either; just made a dusty mess and likely ruined the endmill (which was well used anyway, so no loss). Lastly it turns out the one part was garolite, not phenolic but same difference as far as I'm concerned. That one turned ok, so I don't expect any trouble milling it. I have some doubts about tapping it (more 4-40), but in more of a not-sure-it-will-take-well-to-it kind of way rather than tooling issues. And in further good news I've gotten my hands on the assembly drawing and all that matters is that it all fits together somewhat snugly; actual dimensions don't really matter. That said, my quick and dirty attempt at prepping the material for final drilling put everything within 0.001"...

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                      • #12
                        Careful with fasteners in the Macor if there is any heat involved. We goofed and broke a pricey piece years ago when a mounting screw heated up and expanded.

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                        • #13
                          It depends on the copper: soft or hard.

                          I once did several hundred 10-32 holes in 1/4" thick hard copper. The holes were through so I used a spiral point tap in a tapping head in a drill press. I used Tap Magic for cutting fluid. I started the job with a dozen or so and then turned it over to an inexperienced assistant who finished it. Zero bad holes and zero broken taps. It went zip, zip, zip. One to the next as fast as we could dip the tap in cutting fluid and line it up with the hole.

                          I also did several dozen of them with the tap in a battery powered drill and Tap Magic. Also no problems. Medium speed and the clutch was set for limited torque, not the locked position.

                          In both cases I used the standard 75% tap drill. I did chamfer the holes before taping.
                          Paul A.
                          SE Texas

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

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                          • #14
                            . Lastly it turns out the one part was garolite,


                            Glass filled?
                            Glass filled eats up HSS and carbide both. So does graphite filled. It dulls taps and cutters.
                            When I had to mill some narrow slots I wound up using a diamond impregnated saw blade.
                            Run the vacuum at the same time as you cut and you won't have to worry about breathing the dust.

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                            • #15
                              I work with G-10 quite a lot, I think it's identical to Garolite and it's always glass filled in my experience.
                              I have no trouble machining it with carbide.
                              I avoid tapping it but when pressed I try to use #10-24.
                              If required to tap #4-40 I'd use a new tap and maybe replace it after a few holes.

                              Since this isn't part of the heat transfer maybe you can use inserts?
                              Edit: I guess not, just reread your post.
                              Mike

                              My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

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