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Drilling / Machining question

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  • Drilling / Machining question

    I just took a small job to help pay for some of the equipment I have. I need to do a few operations in some 6061 aluminum. Here is what I have for equipment and this is what I need to do.

    MSC CNC knee mill (5HP)
    Bridgeport mill

    I need to drill a hole in this aluminum 7” deep. The size of the hole is 1 ½” which will be tapped with a 1 ¼” NPT thread. It will have a connector hole, which is only about 1” deep and will have a 1” NPT thread. The CNC Mill quill has only 6” of travel but has a power knee drive but the controller does not operate it. I have the NPT taps and also the tapered reamers. Can anyone give me an idea if I will be able to drill the 1 ½” hole without a pilot? Can you give me an idea on the speeds and feeds? What about reaming and tapping the threads? What steps would you take. There are 28 of these I need to do. There are also some other 3/8 NPT and some mounting holes. This is a type of water manifold. The CNC mill does not control the speed of the spindle so I don’t think I will be able to use the tap in that mill. With the Bridgeport mill have the guts to run the tap and reamer?


  • #2
    I would drill a pilot hole and step up in various sizes to 1.1/2".
    Cutting speeds for aluminum appear to be 50fpm.

    R W


    • #3
      I don't know what to tell you on those deep holes other than what you said but I might be able to help you with the taped holes. If your cnc mill is 3 axis you should be able to thread mill the NPT threads. Interpolate the holes with a tapered end mill, program a spiral interpolation about 1-1/2 to 2 revolutions with a thread mill and their done. If you don't have a NPT thread mill just grind all but 1 flute off of a NPT tap. I am running a similar job right now tapping 1-1/2" NPT threads in a bronze casting with a thread mill, its fast and makes great threads.
      Mark Hockett