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  • Indexible Boring Bar Advice Needed

    Just received a like new Bridgeport #2 boring head w/accessories in original box and would like a recommendation for a good indexable boring bar set. You guys probably know those that work well and those to be avoided.

    This will be my 1st venture into the insert world, and have seen some that claim to be appropriate for use on steel, aluminum, and bronze according to the McMaster Carr website.

    Currently I'd like to be able to cut bronze bushings to an exact .001 repeatedly.

  • #2
    Nothing bugs me more than soft boring bar shanks. You tighten the setscrew and they deform enough to make removal difficult. All the chinese crap have soft shanks. My favorites are Criterion, but I have to watch for those on ebay, etc because they're outrageously expensive. The best bang for the buck IMO is Hertel. Pricing varies.

    Your accuracy requirement of .001 will be easy to achieve with any brand. Hitting that is entirely dependent on operator skill.
    Southwest Utah

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    • #3
      I use a CCMT style insert for my boring bars, I like it because I also have a tool holder for the lathe that uses them.

      Down side to that style insert on a boring head in the mill is it will leave “ridges” for the step over amount on blind or stepped holes.

      I picked up my bars from MariTool.

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      • #4
        It depends on the work.
        A steel shank boring bar extended more then 4 or 5 diameters using a negative rake insert is likely to chatter, positive rake triangle or DCMT inserts with a very small nose radius work best for this.

        A carbide shank bar is best.

        Different tools for different jobs, materials and set ups.

        These are all lathe tools but still apply to milling.

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        • #5
          Originally posted by chipmaker4130 View Post
          Nothing bugs me more than soft boring bar shanks. You tighten the setscrew and they deform enough to make removal difficult. All the chinese crap have soft shanks. My favorites are Criterion, but I have to watch for those on ebay, etc because they're outrageously expensive. The best bang for the buck IMO is Hertel. Pricing varies.

          Your accuracy requirement of .001 will be easy to achieve with any brand. Hitting that is entirely dependent on operator skill.
          I agree, I also have original BP boring head sets. Both size heads. The boring bars that come with the set are somewhat hard but not to the point where the set screw won't chew it up. BP was smart enough to turn a recessed surface for the set screw to seat against.

          JL............

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          • #6
            I'm finding a few different versions of this. Are any of them good?

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            Last edited by Spindle; 11-24-2021, 05:27 PM. Reason: added image

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            • #7
              Those look to be all from a set that comes in that case. And if they are all in the same case with the same looking product then they likely all come from the same factory and just get different distributor names added.

              How much does the whole set cost? That's a good first sign of quality level.

              One good feature is the milled flat for the setscrews. That's a good start.
              Chilliwack BC, Canada

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              • #8
                Originally posted by Spindle View Post
                I'm finding a few different versions of this. Are any of them good?

                Click image for larger version Name:	insert boring bars.png Views:	0 Size:	633.1 KB ID:	1971789
                They can work, depending on application. It's been my experience that those larger ones where the shank diameter is larger than the mounting diameter tend to work less as a cutting tool and more as a musical instrument.

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                • #9
                  Originally posted by Bented View Post
                  It depends on the work.
                  A steel shank boring bar extended more then 4 or 5 diameters using a negative rake insert is likely to chatter, positive rake triangle or DCMT inserts with a very small nose radius work best for this.
                  Thanks for the detail, that's what I need.

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                  • #10
                    Originally posted by BCRider View Post
                    Those look to be all from a set that comes in that case. And if they are all in the same case with the same looking product then they likely all come from the same factory and just get different distributor names added.

                    How much does the whole set cost? That's a good first sign of quality level.

                    One good feature is the milled flat for the setscrews. That's a good start.

                    Those are different sets from different vendors, bottom one $143, top one's $153.

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                    • #11
                      Originally posted by tom_d View Post

                      They can work, depending on application. It's been my experience that those larger ones where the shank diameter is larger than the mounting diameter tend to work less as a cutting tool and more as a musical instrument.
                      Yeah our old friend resonance. I have a defective Enco boring facing head that plays a tune with any bar at any speed...

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                      • #12
                        Steel boring bars from a reputable manufacturer are generally made from tool steel, cheaper options tend to be EN24T, and who knows what steel comes from the far east. In a boring head my recommendation would be a DCGT style inserts as there's not as much push off as a CCMT. If you want an insert that will cover more applications go for a cermet grade as they have a far sharper edge than carbide and will successfully machine non ferrous as well as steels and stainless.

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                        • #13
                          Thanks for all the good advice, I'll continue to learn about inserts, but for right now I'll see what I can do with a new set of cobalt bars. It doesn't seem like cutting sub 1" simple bronze bushings should require anything exotic. I was using an old Everede boring head with an HSS bar that had been improperly sharpened and it dragged on the surface above the cutting tip. Ground that angle back, got a good surface finish but could not repeat multiple .010 diameter cuts. Then tried a cemented carbide bar that also dragged the same way. Seems like the head might be holding the bars at an angle, and I've read that those cheap carbide bars may not have the right geometry anyway. I'll look at them with the optical comparator just for fun.
                          Will give the Bridgeport a trial run tomorrow.

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                          • #14
                            Originally posted by Spindle View Post
                            It doesn't seem like cutting sub 1" simple bronze bushings should require anything exotic.
                            Originally posted by Spindle View Post

                            Currently I'd like to be able to cut bronze bushings to an exact .001 repeatedly.
                            Im not exactly sure what you are doing or how many you have but maybe a reamer would be a better solution for this job?

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                            • #15
                              Originally posted by Spindle View Post


                              Those are different sets from different vendors, bottom one $143, top one's $153.
                              For that sort of money I think you're looking at fairly low end options. I'm thinking that properly heat treated options are going to cost a fair bit more than that. But I'd be interested in what anyone else that owns a set has to say too. If they are properly heat treated and decently made then that's a great price.

                              Something to try for doing bronze would be to use a regular HSS 1/2" end mill. Try it as per normal.. Then since it's bronze try putting a small neutral or slightly negative edge as per the diagram for drill bits. For the bronze this might give you a nice clean cut. And it's the perfect place to re-purpose dull end mills if you're like me and have no way to sharpen them. It only requires that one tooth be sharp. And it's easy enough to grind them back a fair ways to get up where the side edge is keen as well.

                              If you try this you just need to set the position of the tooth so it's dead on axis or slightly raked back so the side edge maintains cutting cearance.

                              I've been using repurposed end mills for my lathe boring for a couple of years now with great results. The design of the end mills seems to resist chatter nicely.
                              Chilliwack BC, Canada

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