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do boring bars need hardening?

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  • do boring bars need hardening?

    Making a couple of 3/4" boring bars out of hardened rod. Annealing now. Should I re-harden after machining. Bars will be 10" and 6". Thanks.

  • #2
    If you think you might bend them in use you can, otherwise there is no point. Usually the work gives first tho.
    "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."

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    • #3
      If you just want it to be stiffer (to resist chatter), don't bother as hardening it won't make it any stiffer (search a bit on the forum if you like, it's been discussed before).


      .
      Thomas

      Problems worthy of attack prove their worth by hitting back
      - Piet Hein

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      • #4
        Hardening will stop it getting scratched to bits by the swarf it creates, and may help to stop the seat of the insert suffering, if that's the way you are making it.

        Hardening is a good idea, but the downside is that after hardening it may not be as straight as it was before the heat treatment. But since it's not a part that has to fit with other parts a slight bend shouldn't be a problem if it happens.
        Richard - SW London, UK, EU.

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        • #5
          My thought would be to not harden it, or if you do temper it well. A boring bar can take quite a load at times. I know hardening won't make it stronger, but I wonder if it changes it's acoustic properties. It would be interesting to see if the resonant frequency changes at all. I suspect it doesn't, but don't know.

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          • #6
            To make it clear, hardening does not make the part stronger or harder to bend elastically. It only makes it harder. It will make it possible to bend it further before it deforms permanently but it doesn't make it harder to bend to the same point that the unhardened part would begin to deform. That applies to all steels, alloy or not. They also all have about the same resistance to elastic bending no matter what the alloy.

            What does vary depending on alloy and condition is how much force it take to permanently deform the part.

            In other words, hardening a boring bar makes no difference to performance.
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            • #7
              Originally posted by Evan
              To make it clear, hardening does not make the part stronger
              Uhm Ok ---------
              It will make it possible to bend it further before it deforms permanently
              Yeah see that's that part that im having trouble with --- that would be called "stronger" because it takes MORE LOAD to bend it further

              In other words, hardening a boring bar makes no difference to performance.

              No, wrong "to make it clear" hardening a boring bar make's it not only stronger but more resilient, plain and simple it will be capable of handling MORE load without any permanent damage --- plain and simple it WILL make it stronger...

              Also like stated --- it will make it resist gouging and as we all know boring bars choke on their own soup so this is important -------- harden the damn thing - set it and forget it.... it will make it BOTH stronger AND more resilient...
              Last edited by A.K. Boomer; 06-10-2012, 12:58 AM.

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              • #8
                Originally posted by A.K. Boomer
                Uhm Ok --------- Yeah see that's that part that im having trouble with --- that would be called "stronger" because it takes MORE LOAD to bend it further


                No, wrong "to make it clear" hardening a boring bar make's it not only stronger but more resilient, plain and simple it will be capable of handling MORE load without any permanent damage --- plain and simple it WILL make it stronger...

                Also like stated --- it will make it resist gouging and as we all know boring bars choke on their own soup so this is important -------- harden the damn thing - set it and forget it.... it will make it BOTH stronger AND more resilient...
                You are correct Boomer, the yield strength does change, but the modulus of elasticity does not. As Evan explained, basically, until you reach the point of permanent (plastic) deformation of the bar, the bar will react, and deform (bend) the same amount given the same force whether it is hardened or not. Maybe others have, but I have never successfully bent an unhardened boring bar, nor broken one. Given that I have stayed within the elastic limits of the bars (never bent one), hardening would make zero difference on the performance of the bar for me. Regarding gouging/damaging the bar, I would much rather a boring bar get marred up than something expensive.
                "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."

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                • #9
                  No, wrong "to make it clear" hardening a boring bar make's it not only stronger but more resilient, plain and simple it will be capable of handling MORE load without any permanent damage --- plain and simple it WILL make it stronger...
                  It will not make it stronger in any way that matters to a boring bar. It also won't be more "resilient", whatever that is. Resilience isn't a property of metal and it isn't anything you want to have in a boring bar anyway. Hardening increases the metal's absolute failure strength, it's true. That is irrelevant to a boring bar.
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                  • #10
                    I usually buy mine "ready to use" as a set with the holder/clamp and use them "as is".

                    If I have to make one I just use plain common old "hot-rolled" and drill/machine it as required. I usually use sound HSS bits (easier to make a round hole than a square one and I can "tilt" the tool to adjust side clearance and rake). I sometimes MIG well the tool to the bar or else silver brase it - what works works. Welding doesn't seem to affect the HSS tool too much if I am careful

                    If I ever have a problem its usually to do with tool shape or excessive speed or feed or depth of cut. I just "back off" until its woking OK and leave it at that.

                    Boring tools need to be dead sharp and hand-honed as required.

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                    • #11
                      I should point out that when I say "stronger" what I really mean is "stiffer". That is what a lot of people consider to be "strength", as in more difficult to bend below the point of permanent deformation.

                      Stiffness is an intrinsic property of metallic elements and the predominant metal in iron alloys is, of course, iron. The stiffness of iron will be the main factor although there will be some small differences in stiffness in very high alloy steels.

                      For very superior boring bars tungsten alloys are far better. It has about three times the stiffness of iron for the same dimensions. They cost much more but the difference is large.
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                      • #12
                        Really depends how hard he's pushing his boring bar,

                        the OP is "do they need hardening" - for the most part I agree the answer is no, unless you make the occasional bottoming out mistake or something of that nature...

                        But - my beef was with Evans statement that it does not make it stronger - it does, plain and simple -- and if your maxing out your bar or have the occasional bottoming out against the inner facing wall then it can make all the difference in the world.

                        Resilience is the ability to bounce back after an "incident"

                        and a hardened bar has that ability more so than one that is not...

                        It is a term used in many of metal quality and properties books.

                        My new world dictionary describes just how I used the word;

                        Resilience; a) The ability to bounce or spring back into shape, position, ect.
                        b) The ability to recover strength, spirits ect.

                        Now --- you state that resiliency isn't even a property of metal? really?

                        definition "a" is widely used to describe certain metals and there properties...

                        And you also state that it's not even a property you would want in a boring bar anyways? really ? im stating BS, it sure the hell is....

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                        • #13
                          But - my beef was with Evans statement that it does not make it stronger - it does, plain and simple -- and if your maxing out your bar or have the occasional bottoming out against the inner facing wall then it can make all the difference in the world.

                          Never will it make a difference that matters. By the time the deflection is to the point of reaching deformation you already have a crash. Before that point there is no difference at all.

                          It is a term used in many of metal quality and properties books.
                          What is the "resilience" value of 1020 mild steel?
                          Last edited by Evan; 06-10-2012, 03:50 AM.
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                          • #14
                            Originally posted by Evan
                            I should point out that when I say "stronger" what I really mean is "stiffer".
                            that's all I was after - im not trying to badger you about it - I just wanted to clarify the difference

                            For very superior boring bars tungsten alloys are far better. It has about three times the stiffness of iron for the same dimensions. They cost much more but the difference is large.

                            What about carbide as far as stiffness - it's pretty good right?

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                            • #15
                              What kind of carbide?
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