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  • 2" or 3" Boring Head?

    It's for a Grizzly 8 X 30 mill.

  • #2
    There's a time and a place for every tool. You can certainly use a 3 inch, but the 3 inch is bigger in all directions (and heavier too) and may not fit into places you need to get into.
    At the end of the project, there is a profound difference between spare parts and left over parts.

    Location: SF East Bay.

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    • #3
      I have the Enco version of that mill. If they have not changed the pulleys, your minimum RPM is 230.

      Your minimum RPM will dictate the max diameter you can cut with HSS and carbide.

      If you are using HSS it will limit your boring to about 2 inches in mild steel. If you use carbide tools you can run at a higher cutting speed and larger bores.

      I have considered adding a VFD to allow me to reduce the spindle speed.

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      • #4
        All depends on the range of bore sizes you want to produce, diameter x length. I have both, a 2" with a short 3/4" straight shank, good for quick jobs because it uses up so little Z height. And a 3" Bridgeport brand 3" with an R-8 shank, which of course works well for larger and deeper bores, but consumes Z height rapidly.

        If you are looking at the 2" import models, pay attention to the design. There are two piece heads and three piece heads. The two piece have the dovetail jib machined into them, the three piece have a separate jib piece. The three piece are a PITA to keep the jib from loosening up.
        I just need one more tool,just one!

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        • #5
          I have both for my BP.

          JL.....

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          • #6
            A timely thread for me, as I have just been looking at buying a boring head for my Rong Fu 25. It will have to be a 2" (50mm), but the drawback with that size is that it takes boring bars with a shank diameter of 12mm.

            A set of brazed carbide 12mm boring bars is dirt cheap (we're talking AliExpress here), but the 12mm insert-holding type of round bar is eye-wateringly expensive. Chinese brazed carbide tools in my limited experience are rubbish, but I suppose that as I will not be using the tool very often I should get useful life out of the set.

            Oddly, the insert type of the larger bars used in the larger boring head are comparatively cheap.

            Weirdscience, I hadn't twigged that about the two-versus-three-piece construction. Many thanks!

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            • #7
              Well, I've gone ahead and ordered one. This one, in fact:



              Weirdscience, it seems to be of the two-part persuasion, with the gib looking like a slightly flexible bit at the top of the main part.

              It will take a few weeks to arrive from China, especially as NZ is totally locked down at the moment, and freight is a sometimes thing, but I'll let you know the outcome in due course.

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              • #8
                I've had extremely good luck with a shars 2". Even with the tiny numbers my bores tend to be dead on. I wish I had a 3 or 4 inch for the type of work I do, as I usually only need it for enlarging bores I cant drill (over 2") though I do have a boring job coming up here.

                E: looks the same exact unit Mike.
                21" Royersford Excelsior CamelBack Drillpress Restoration
                1943 Sidney 16x54 Lathe Restoration

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                • #9
                  Hi,

                  I have a 1 1/2" Criterion for my little G0704 mill. I love that little thing. But I would like to get a decent 2" also. The single tool holding hole in the Criterion is quite range limiting.

                  Your mill should be able to deal with a "standard" 3" quite well. Just remember, the more you need to extend the head to bore a larger hole, the more unbalanced it becomes as you spin it. Depending on your needs, a 3" should not need much extension and should therefore stay more balanced. Which also allows for higher rpms and a generally better accuracy and finish.
                  If you think you understand what is going on, you haven't been paying attention.

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                  • #10
                    Originally posted by Mike Burch View Post
                    A timely thread for me, as I have just been looking at buying a boring head for my Rong Fu 25. It will have to be a 2" (50mm), but the drawback with that size is that it takes boring bars with a shank diameter of 12mm.

                    A set of brazed carbide 12mm boring bars is dirt cheap (we're talking AliExpress here), but the 12mm insert-holding type of round bar is eye-wateringly expensive. Chinese brazed carbide tools in my limited experience are rubbish, but I suppose that as I will not be using the tool very often I should get useful life out of the set.

                    Oddly, the insert type of the larger bars used in the larger boring head are comparatively cheap.

                    Weirdscience, I hadn't twigged that about the two-versus-three-piece construction. Many thanks!
                    is this too expensive?

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                    • #11
                      Great info! Keep it coming!

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                      • #12
                        That one from Aliexpress looks identical to mine near as I can tell from the picture. I admit that I've only used it about 8 or 10 times. But when I did it always did the job easily and was accurate in the movements of the dovetail for getting the size just right.
                        Chilliwack BC, Canada

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                        • #13
                          Originally posted by Mike Burch View Post
                          A timely thread for me, as I have just been looking at buying a boring head for my Rong Fu 25. It will have to be a 2" (50mm), but the drawback with that size is that it takes boring bars with a shank diameter of 12mm.

                          A set of brazed carbide 12mm boring bars is dirt cheap (we're talking AliExpress here), but the 12mm insert-holding type of round bar is eye-wateringly expensive. Chinese brazed carbide tools in my limited experience are rubbish, but I suppose that as I will not be using the tool very often I should get useful life out of the set.

                          Oddly, the insert type of the larger bars used in the larger boring head are comparatively cheap.

                          Weirdscience, I hadn't twigged that about the two-versus-three-piece construction. Many thanks!
                          Mike, I use 12mm SCLCR bars in my 2" boring head (6x26 mill). I bought 3 and cut them to different lengths, plus an SCLCL left hand bar for mounting the bar side ways or doing the outside of bosses. That way I can use the same inserts as I do on my lathe. I also made a 1/2 to 3/8" bushing for my smaller HSS boring bars, plus I'll probably be making more to repurpose my smaller steel SCLCR boring bars as I replace them with solid carbide versions. You do need a range of sizes as bigger bars can't always get into small holes.

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                          • #14
                            Second what Matt said, with a 2" used creatively you can go much larger than a 2" bore. I think a 2" is sized more appropriately for that size mill. Take a look at this site for some good ideas for rigid boring setups:

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                            • #15
                              Had the same dilemma and I compromised and got a 2 1/2" APT (I think is the brand), It has worked out well, no complaints with it. The price was reasonable too. I got the model with a separate screw in shank, would get the one piece if I was doing it again, then it could be run in either direction. But this hasn't been a problem yet either. I have a Rockwell vertical mill.

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