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  • #31
    Originally posted by J Tiers View Post

    Hmmmmmmmm

    Modulus of elasticity may not change, but I've seen the chinese boring bars just snap off like glass when they should not. Hardened and apparently not tempered right.
    That can happen. Too low of fracture toughness, even if stress is below yield. Here is a picture of the one I made, double ended. One end a square hole for through bore, and the other end for shoulder boring. I use the shoulder end 99% of the time. Mild hot rolled bar. Click image for larger version

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    21" Royersford Excelsior CamelBack Drillpress Restoration

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    • #32
      I bought a new Kennametal 5/8" with their carbide inserts a few years back,was pretty disappointed how it performed.First of their products I did not like.

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      • #33
        Originally posted by The Metal Butcher View Post

        Incorrect. I've had this same argument with Adam Booth. As said before, modulous of elasticity does not change much across steels. I am very happy with my homemade 5/8"x12" boring bar. I've had good results with it when my (admittedly smaller) inserted bars weren't cutting it. @OP, I'm with others. It is trivial to make your own.
        I couldn't give a rats ass about the modulus of elasticity, I know how they work. They are CRAP, chatter terribly and bend away from the work. On my lathe,I generally use the HSS boring bars that are made for boring heads, for short length holes, they work great. No chatter no flex.

        To many people here forget that a lot of us are not working in commercial shops and what is good for them isn't always good for us. If HSS works fine for you then use it and it is cheaper.
        The shortest distance between two points is a circle of infinite diameter.

        Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

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        • #34
          Originally posted by Rich Carlstedt View Post
          SO I silver solder some HSS to a piece of key stock and drilled a hole at 8 degrees ( relief) , then ground it to one half diameter, done
          Click image for larger version

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          What kind of twist drill drills high speed steel?

          metalmagpie

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          • #35
            Originally posted by loose nut View Post

            I couldn't give a rats ass about the modulus of elasticity, I know how they work. They are CRAP, chatter terribly and bend away from the work. On my lathe,I generally use the HSS boring bars that are made for boring heads, for short length holes, they work great. No chatter no flex.

            To many people here forget that a lot of us are not working in commercial shops and what is good for them isn't always good for us. If HSS works fine for you then use it and it is cheaper.


            Originally posted by The Metal Butcher View Post


            Incorrect. I've had this same argument with Adam Booth. As said before, modulous of elasticity does not change much across steels. I am very happy with my homemade 5/8"x12" boring bar. I've had good results with it when my (admittedly smaller) inserted bars weren't cutting it. @OP, I'm with others. It is trivial to make your own.
            I have been reading about this in the forums for actually years.
            I understand elastic modulus. I have 2 pieces of paper to prove it.
            What I know about boring bars is this...
            Stress is how much force is put on something.
            Strain is how much it bends.
            If you harden a boring bar, it bends less when in use.
            It also resonates at a higher frequency than a soft bar.
            Just tap them on the table and listen.
            When using a boring bar, you do not want bending.
            That means spring in the cut. Spring is bad.
            You want the lathe (or mill) to take the depth of cut that you dial on the screw.
            You also do not want low frequency vibration. This means chatter.
            Soft bars are bad for this.
            High frequency vibration is better in a way.
            At least the finish left is finer, not all rocky and bumpy.
            If the frequency is high enough, it will not resonate at all.
            This is best for a good finish.



            https://www.quora.com/Does-quench-ha...lastic-modulus
            Ares Alecto, studied Materials Science and Engineering
            Answered Jan 25 · Author has 158 answers and 143.2k answer views








            I looked at some of the discussions and surprisingly this is a topic where scientists seems argue a lot. The answer is, it will change of course due to the chaotic nature of the universe and crystal structure is a very big parameter in steel effecting everything. Is it significant enough to put in calculations is another matter where all the problem comes from. If you are designing a spaceship, it matters. It matter a lot. If it is an ICBM missile part, yeah sure but in normal applications, the difference mostly got lost in the safety factor.
            See the elastic modulus is about the area where the chemical bonds between atoms stretched reversibly. So even if you change the crystal structure, say like with quenching, you still have the same composition of materials and same bonds. This is the part supporting the “won’t change” argument.
            The other part is (I deduce) the change in Cementite phase composition. Cementite is basically an interstitial carbide (which means small carbon atoms reside in the interstitial space between big iron atoms) and therefore a ceramic.

            Ceramics are not metals and also not a part of steel. It has very different characteristics than metals and have ultra high elastic modulus no because of their high tensile strength (on the contrary they are terrible at tensile load) but due to their very low elongation. This gives a different slope than the steel these Cementite phases reside in.
            Since the Cementite phase density can be adjusted with heat treatment, the change in the elastic modulus of steel will be tied to this density.




            ………...Read the last paragraph.
            This is what I believe is the key to understanding what is going on here.
            The Cementite (or read, Iron Carbide) must be considered separately with
            regards to it's elastic modulus verses the elastic modulus of the base steel.
            The whole "package" must be considered. The Iron Carbide adds to the
            elastic modulus of a base steel, and the whole bar is more stiff. I believe
            this explains what many machinists are seeing with the better cutting
            performance associated with hardened steel boring bars.
            --Doozer
            DZER

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            • #36
              I have yet to see any mention of forging as having an effect. Does a forged then appropriately hardened bar perform better than one with just hardening alone?

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              • #37
                Forging is workhardening.

                -D
                DZER

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                • #38
                  Originally posted by Norman Bain View Post
                  I have yet to see any mention of forging as having an effect. Does a forged then appropriately hardened bar perform better than one with just hardening alone?
                  Depends on what the other option besides forging is. If the other option is casting, then yeah, forging usually results in a stronger product. If the other option is something like machining from a billet, there's not gonna be much difference

                  Also, forging can work garden pieces, which is completely undone by the actual hardening process. A forged knife and the unforged stock coming from the same bar as the knife will harden and preform the same

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                  • #39
                    Doozer, you copied the wrong answer from quora

                    Hardness has some minute effects on modulus of elasticity but for practical purposes its all the same
                    https://www.amesweb.info/Materials/Y...-of-Steel.aspx

                    Gray cast iron is different animal
                    https://www.engineeringtoolbox.com/y...lus-d_773.html

                    The chinese boring bar might break because its too hard or the setscrews can be crappy and too small or the bar can be too soft and the "insert" pocket deforms easily.
                    But its equal stiffness until you load it with WAY too much force moving from elastic deformation to permanent(plastic) deformation. Softer one is also less likely to vibrate.

                    Boring bars are by nature pretty prone to vibration and I'm guessing many of us are blaming the chinesium material (and themselves when they bought the cheapo boring bar).
                    If you have "Proudly Made In 'Murica" hardnened, tempered and spit-polished boring bar you are less likely to ditch it first time it starts to vibrate but continue to experiment and find a cure for the vibration because you know that the boring bar has to be good
                    Last edited by MattiJ; 12-02-2019, 04:24 PM.

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                    • #40
                      M35 HSS may be a bit stiffer: http://www.astmsteel.com/product/too...6-5-2-5-skh55/

                      Molybdenum has a much higher modulus of elasticity, and retains most of it to 1000C: https://www.molybdenum.com/propertie...enum-physical/

                      Alumina and Zirconia porcelain ceramic also have very high stiffness, although may not be suitable for a boring bar: https://www.engineeringtoolbox.com/c...es-d_1227.html

                      Tungsten and various carbides are about 2x stiffer, and other exotic materials can be orders of magnitude stiffer:
                      https://en.wikipedia.org/wiki/Young%27s_modulus

                      Carbyne is 150 times stiffer than steel!

                      Grain oriented materials, and possibly certain treatments, may increase stiffness in certain orientations, so perhaps forging may accomplish this.

                      Practically speaking, I wonder if it may be possible to cast a boring bar with prestressed metal reinforcing rods to increase stiffness?
                      http://pauleschoen.com/pix/PM08_P76_P54.png
                      Paul , P S Technology, Inc. and MrTibbs
                      USA Maryland 21030

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                      • #41
                        Originally posted by MattiJ View Post
                        Boring bars are by nature pretty prone to vibration and I'm guessing many of us are blaming the chinesium material (and themselves when they bought the cheapo boring bar).
                        If you have "Proudly Made In 'Murica" hardnened, tempered and spit-polished boring bar you are less likely to ditch it first time it starts to vibrate but continue to experiment and find a cure for the vibration because you know that the boring bar has to be good
                        I don't think its a valid comparison unless the steel in both bars has the same analysis and the same heat treatment. And they certainly won't give you that information. Only thing in favor of the American manufacturer is that you will probably have better product support as opposed to some importer who is not a manufacturer.

                        I have used tooling from all over the world at various times. All countries are capable of making good tooling, Many make crap too. Yes, even the Germans. The only one that always makes good tooling is the Swiss. But nobody can afford them. Buying American is a political decision for me: giving the local guy a job, at a time when decent jobs are scarce.

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                        • #42
                          Originally posted by PStechPaul View Post
                          Probably thanks to high percentage of Tungsten and Molybdenium.

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                          • #43
                            Perhaps it would be possible to make a stiffer boring bar by boring a hole through a steel bar and shrink fitting a tungsten carbide rod in it.

                            https://www.mcmaster.com/tungsten-alloys
                            Last edited by PStechPaul; 12-02-2019, 05:31 PM.
                            http://pauleschoen.com/pix/PM08_P76_P54.png
                            Paul , P S Technology, Inc. and MrTibbs
                            USA Maryland 21030

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                            • #44
                              Originally posted by PStechPaul View Post
                              Perhaps it would be possible to make a stiffer boring bar by boring a hole through a steel bar and shrink fitting a tungsten carbide rod in it.

                              https://www.mcmaster.com/tungsten-alloys
                              Hi,

                              That just sounds like a solid carbide bar with extra steps.
                              If you think you understand what is going on, you haven't been paying attention.

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                              • #45
                                Originally posted by metalmagpie View Post

                                What kind of twist drill drills high speed steel?

                                metalmagpie
                                Just my ordinary American made drills, like Cleveland or Latrobe--- but what I left off in the post was
                                the heat treat (hardening) after drilling and before grinding . The material was Starrett stock
                                You can do it so fast that the silver solder does not melt and I keep a ice/water cup nearby for the "dunk"
                                Rich
                                Click image for larger version

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