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Boring bar problem

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  • Boring bar problem

    I recently bought this Interstate NBN-6-2 boring bar to do some fairly deep boring on a project.

    It seems to cut OK, but I soon found that the cutting tip is a little behind the shank diameter. In other words, with the bar square to the work, the shank hits the edge of the hole cut by the insert.

    Did I have an unrealistic expectation, or am I overlooking something stupid?


    For just a little more, you can do it yourself!

  • #2
    You are generally depth limited to 2.5 -3 times the diameter, so it looks "about right". Of course, we all cheat on that now and then , but you can't with this bar. I have a few limited like that, but also many that are not.

    If it bugs you grind off the front edge.

    I have solid carbide bars that are good for 10X diameter... love those.
    Last edited by lakeside53; 03-07-2015, 10:28 PM.


    • #3
      I have a gang of boring bars. From some really nice and small 1/4" to for me, heavy duty 1" in steel and carbide, heavy that carbide 12x1" bar. Ironically the carbide insert is mounted on a tool steel "holder" that is the end of the carbide bar. Still gotta use some steel, I think it cushions the insert also.

      It was interesting AND informative with what Lakeside said. I have never seen a boring bar with built in limits. I don't suppose its a bad idea for the market they work with. I learned something new today. Good Day.. JR
      My old yahoo group. Bridgeport Mill Group


      • #4
        Yep that is just how they work. that is why round bars and a holder are popular, you can get the EXACT stickout you want. Although having a non fixed height (as tool can rotate) is a blessing and a curse.

        You are generally expected to get a whole set of different length carbide insert bars.. and different diameters. This is why I find the $20 9pc brazed carbide boring bar sets such a great deal. You get a size/length for most occasions. When you need a big hole turn to your carbide insert bars, only need a few then (as they are pricy) of various stick out lengths.
        Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


        • #5
          Interesting design. Ironic, made in USA to a crappy Chinese standard?

          Send it back and get a name brand that takes a CCMT/CCGT, a CPMT/CPGT, or WCMT/WPGT.

          Failing that, are you sure you've got it in the correct orientation? If you are holding it in a QCTP block type 1 or 2 using set screws on the flat top of that bar, all you should have to do is set center height and go. If holding it in a No.4 boring bar holder be sure that flat is level then set to center. If the steel of the bar still rubs then it's a POS and you should get rid of it.


          • #6
            I may do it totally wrong, but a lot of times I angle my BB. Is this a no no ?
            John Titor, when are you.


            • #7
              It's fine unless you want the insert to cut the bottom of a hold shoulder dead straight etc.


              • #8
                Originally posted by ed_h View Post
                It seems to cut OK, but I soon found that the cutting tip is a little behind the shank diameter. In other words, with the bar square to the work, the shank hits the edge of the hole cut by the insert.
                Isn't that what grinders are for?


                • #9
                  YEP! I've modified many tools to get into a tight space...


                  • #10
                    It just seems like a silly limitation. The bar is 5" OAL, but it's mostly shank that can't go into the bored hole. Moving the insert tip out maybe 0.020" would have avoided the problem.

                    I can grind it, but I shouldn't have to. This bar wasn't cheap by my standards--$40+ without the insert.

                    For just a little more, you can do it yourself!


                    • #11
                      What lakeside said...Micro 100 for one makes a lot of their smaller brazed tip boring bars in a configuration that does the same thing, IMO its two things, the limitation as lakeside said but in
                      Micro 100 example perhaps that even the smallest bars have a common shanks size of 1/2" so you don't have to putski around with shims/spacers/split thingies in the holder (I don't have any of those Micro 100 boring bars but it could be that the larger diameter is of a length that allows good clamping and the rest can go into the bore without hitting, tough to tell scale looking at sellers photos)


                      • #12
                        Interesting observation I have not encountered not having insert holders. It seems to be the all too common result of a designer being far removed from the actual use and no hint of proper field testing.
                        Ok you wouldn't expect people to think of trialing such a simple item but it would have shown up the shortcomings and lead to a decent product. So often I have bought somthing (normally rather more complex) and wished I could be a reviewer for a magazine that tested products and was permitted to make honest reports rather than sucking up to the advertising revenue.


                        • #13
                          Boring bars are always limited by a compromise between diameter and rigidity.

                          I won't say that you are being unrealistic, but the specs for that bar should have stated its maximum boring depth, which would be limited to the length of the reduced shank portion. If that reduced shank portion was larger, it wouldn't be able to bore to the same minimum diameter. If it was longer, you would lose rigidity. If the full sized shank part was smaller, you would again lose rigidity and it wouldn't fit into standard boring bar holders. What it comes down to is that the manufacturers expect you to match the boring bar to the job, and buy more of their expensive boring bars.

                          If no maximum boring depth was listed for the Interstate bar, you may have a legitimate gripe with the seller. Many if not most other makes do list maximum depths in their specs.

                          Again, boring tools are always a compromise. Had the reduced shank portion been longer, you might have been complaining about excessive chatter.


                          • #14
                            Let's back up one minute.

                            It occurs to me (far too late) that every insert or solid carbide boring bar I've ever bought or used gives a minimum bore diameter that it's rated for. In this case, I looked up that boring bar on MSC's website (the Interstate brand is theirs) and it clearly states "minimum .430" bore" for that one.

                            What size hole are you trying to stuff it into?


                            • #15
                              Originally posted by Mike Amick View Post
                              I may do it totally wrong, but a lot of times I angle my BB. Is this a no no ?
                              Just a nooby but I do this most of the time
                              Agua Dulce, So.California
                              1950 F1 street rod
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                              1953 chevy 3100 AD for 85 S10 frame have a 4BT cummins motor, NV4500
                              1968 Baha Bug with 2.2 ecotec motor, king coil-overs,P/S