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another boring bar question

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  • another boring bar question

    I have a six inch ~sq al plate with a 1.35" hole in it. The hole is 3/4 from the bottom of the plate and centered. I want to cut a lip around the hole about .01" and .1" deep.

    How would I do this with a boring bar ? Do I just center the spindle and put the boring bar holder in and adjust out to the edge of the hole ?

    I guess I am having a problem finding the exact center of the hole. The plate is not exactly square so finding the exact center is proving difficult.

    Any suggestions ?


    This mill stuff is a lot different than the lathe The plates a little to big to swing on my 10" lathe because the hole is off center

  • #2
    Clamp the plate to the table, put the indicator in the spindle, and indicate off the inside of the hole. Once zeroed the spindle is on the center line of the hole. Adjust your boring bar out to touch the edge of the hole, and add another 0.01.


    • #3
      So it looks like you got the four plates bored out stacked up and now need to bore a counter bore in them.

      Clamp the plate to the table, use a co-ax indicator to center the spindle over the bore, put the boring head in the spindle and adjust the cutter out to where it just touches the bore. Then adjust the cutter out .050", lay the cutter on the surface of the work, lock the quill, set the knee dial on "0", back the knee down a little, start the spindle at the desired rpm, feed the knee up untill you cut a .010" deep cut. Then back the knee down, stop the spindle, adjust the cutter out another .050", start the spindle, feed the knee up to a .010" deep cut as before and drop the knee and your done.

      Do all four as described above. If your brave do the counterbore in one pass instead of two .050" cuts.

      Have fun.

      EDIT: opps, I had the depth and diameter of the counterbore reversed. My bad.
      Last edited by Carld; 09-15-2010, 09:45 PM.
      It's only ink and paper


      • #4
        So that's how you use a co-ax indicator. I wish I had one.


        • #5
          Originally posted by kben77
          So that's how you use a co-ax indicator. I wish I had one.
          Got a regular indicator?


          Shim material?

          Feeler gages?

          There`s other options if you don`t have a coax indicator. To get the right depth, you`ll probably need to `touch off`to set a zero point for the 0.100depth anyway.

          What are the dimensions of the stepped bore? 0.010 wide by 0.100 deep? Seems right on the order of what you might get for two passes, one to rough out and one to finish.

          My $0.02, YMMV
          Design to 0.0001", measure to 1/32", cut with an axe, grind to fit


          • #6
            Depth is not critical, width is. I did bore the hole thru the four plates and then unstacked them. The bearing has a lip on it and I wanted to bore for it on the four plates. I do have a regular dial indicator and a test dial indicator just having a hard time picturing how I center the spindle over the hole with those.

            I watched a youtube video on the co-ax indicator and wish I had one


            • #7
              You can rig a dial indicator held in the spindle with a little imagination of how to rig it. as long as you can point the plunger at an angle into the bore it will work. You don't have to use all the fancy tools, just a little imagination to rig it and get 'er done.

              My bad, I reversed the diameter and depth of the counterbore in my explanation.
              It's only ink and paper


              • #8
                No worries, I appreciate everyone's help. I know these are basic questions but I have viewed a lot of videos and read a lot of books, but they just don't cover common set up questions. That's why I think this site is a great place


                • #9
                  do you have the dial indicator 22 pcs point set? put the bent one in and give it a spin.


                  • #10
                    Kevin,don't feel alone,I am in about the same boat as you.I can run the lathe and mill but have to think long and hard about every step.
                    I have had times when I wanted to bore to a certain depth and never thought of using the knee dial......even if the question seems elementary there is always something to pick up....big or small.
                    Last edited by BigMike782; 09-16-2010, 12:46 AM.


                    • #11
                      A different approach

                      If you are more comfortable on the lathe why not make a dedicated arbor with one end that fits the hole you are trying to center and the other end to fit a collet in the quill. Install it in the quill and move the table untill the other end enters the hole. This is probably not as accurate as the indicator but may be good enough.
                      Byron Boucher
                      Burnet, TX