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Is a grade 8 bolt a good material to make an insert toolholder out of?

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  • #31
    Because they ARE more rigid
    Rigidity is generally accepted to mean the ability to resist deflection rather than deformation. In this case especially, correct nomenclature is essential to highlight the difference between deflection and deformation. It isn't nit picking since the difference is all important. The word "stronger" is a poor choice as it has no specific meaning or measurement unless qualified.

    It is necessary to use terms that many people are not familiar with to correctly describe the difference between deformation and deflection. "Bending" also doesn't make the grade.

    The hardened bar "feels" "stronger" and more "rigid" because it takes more deflection and hence greater applied force to bring it to the point of permanent deformation. There is even more to that story but it does involve possible eye glazing in respect of the shape of the stress/strain curve for different treatments and alloys of steel. Once into the deformation range of the curve all steels are not the same and that is what produces the impression that some steels are stiffer than others.
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    • #32
      Anybody know what alloys are commonly used for grade 8 bolts?

      I wondered when we had a couple jobs to modify large quantities of them.

      I decided to have the bolts annealed for easier mnachining. After machining they would be sent back to the heat treater for re-hardening.

      Called the US manufacturer to get the alloy which the heat treater needed for the annealing and re-hardening.

      The response I got from the manufacturer was "none of your business"!!

      Huh? They explained the bolts could be made of bubble gumn as long as they met the requirements of the grade 8 spec.

      I paid $75 extra to the heat treater to do a chemical analysis and we were off and running.
      Last edited by DR; 11-02-2011, 03:13 PM.

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      • #33
        If you paid an extra $75 to get an analysis, shouldn't you have gotten a report showing that the material was 4340, 4150, 8620, or ??

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        • #34
          Anybody know what alloys are commonly used for grade 8 bolts?
          Bolts aren't specified by alloy, only by properties. Each grade has minimum specifications for tensile strength primarily and a few other properties too.
          Free software for calculating bolt circles and similar: Click Here

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          • #35
            I know that 1038 is a common composition for bolt heading wire. Not sure if 1038 can produce Grade8 spec or not.

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            • #36
              Originally posted by PixMan
              If you paid an extra $75 to get an analysis, shouldn't you have gotten a report showing that the material was 4340, 4150, 8620, or ??
              I didn't even think about it at the time. It wasn't something I needed to know, only the heat treater needed the composition.

              Now, I'm just curious, wondering if they use alloy steels or plain high carbon.

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              • #37
                I've got nothing to add to the OP's question, but Evans picture of the boring bar reminded me of my machinist friends shop. This guy is 86 years old and is a little crusty. Always willing to answer an honest question, but doesn't suffer fools gladly. He was letting me use a lathe in his shop, and told me to take any tooling I needed from the cabinet next to it. I opened the cabinet, and the top shelf was labelled "Boring Tools". The next shelf down was labelled "More Interesting Tools". I almost fell on the floor laughing!
                Davis

                "Nothing is impossible for the man who doesn't have to do it himself"

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                • #38
                  Originally posted by philbur
                  Trouble is a boring bar doesn't have the same functional requirements as a lockpick or a prybar so the analogy is a bad one.

                  You can push harder because they are stronger not because they are more rigid.

                  Phil
                  phooey.....

                  Perhaps YOU like your boring bars to permanently deform..... To each his own...... I prefer mine to spring back after deflecting, and you may suit yourself.

                  In case you do NOT want your boring bars to bend and permanently deflect, I suggest that the analogy is quite decent.... both tools are commonly long with respect to their diameter, both have a working end to which force is applied more-or-less perpendicular to the axis of the tool, and both must resist that force without deformation.

                  Perhaps you might like to reconsider your hasty statement............

                  Stronger? Well of course they are, but I deny that the "strength" is what is responded to.

                  People are not responding to the ultimate breaking strength, which is not being approached closely. They are responding to the fact that one can push much harder because the tool does not deform...... it has a *spring constant*, along with a larger elastic deflection, and that allows a larger force to be applied at the cost of a bit more temporary deflection.




                  Originally posted by Evan
                  Rigidity is generally accepted to mean the ability to resist deflection rather than deformation.
                  Um.... I did say that I described what was as most folks understand it... pointing out thereby that it is not necessarily the technically correct description.....

                  but obviously deformation is an extreme form of deflection, insofar as the physical results in a structure or machine are concerned....

                  You quibble about the names, I see that the lifting arm is not lifting, but is laying on the ground, bent out of shape. Since that is presumably not the result I had in mind, I am considerably less interested in words, and more interested in the fact that it "deflected" plenty...... and not in a good way.


                  Originally posted by Evan
                  The hardened bar "feels" "stronger" and more "rigid" because it takes more deflection and hence greater applied force to bring it to the point of permanent deformation.
                  I offer you the alternate explanation that it "feels stronger and more rigid" because you can push harder with it. Something that bends out of the way and stays bent (elastic limit was exceeded) is not called "strong" as far as whatever usage it was put to....
                  1601 2137 5683 1002 1437

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                  • #39
                    I made these little boring bars out of a soft steel, not sure what it was, it machined beautifully like lead alloy steel does. They work fine for what I've used them for which is in the lathe and my BP boring head. I use a good sharp carbide insert in them and have never had them chatter.

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


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                    • #40
                      Nice work, Joe.

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                      • #41
                        A SAE Grade 8 Bolt is supposed to be made from alloy steel (per IFI)... which would mean typically 41XX range.

                        I cant remember exactly what, but for steel to be an "alloy" there are certain chemical mix between 1 or 2 of the elements.. I am pretty sure its carbon and them maybe something else.

                        When I get to work I will be able to say for sure as I have the IFI book

                        Edit to add... Right from the IFI book 7th ed. Carbon steel is classed as an alloy steel when the mx of the range content specified for manganese is greater than 1.65% or for silicon .60% or for copper .60% or when the chromium content is less than 4.0% (if greater it approaches stainless) or when the steel contains a specified min conten of aluminum, boron, cobalt, columbium, molybdenum, nickel, titanium, vanadium, zirconium or any other element added to achieve a specific effect. Litterally dozens of differnt carbon alloy steels are usef r fastener manufacture. Some of the more poopular are AISI 1335 (Mg) 4037(Mo), 4140 (Cr,Mo) 4340 (Ni,Cr,Mo) 8637 (Ni,Cr,Mo) and 8740 (Ni, Cr,Mo)

                        Goes on to say more. Also in the charts of the book it calls for medium carbon alloy steel, the product is quenched and tempered. Grade 5 calls for medium carbon steel that is quenched and tempered
                        Last edited by cuemaker; 11-03-2011, 09:40 AM.

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                        • #42
                          The most common functional failure of a boring bar is chatter. Chatter is a result of the applied force causing elastic deflection. The stress level needed to cause this type of failure is way below that required to cause permanent deformation (bending). You will stop a boring operation due to chatter long before you get even close to bending the bar.

                          The most common functional failure of a lock-pick or a pry-bar is permanent deformation, it got bent! This permanent deformation is due to the applied force taking the material past its elastic limit.

                          So to perform their respective functions a boring bar needs a large modulus of elasticity to resist elastic deflection (to avoid chatter) and a lock-pick and pry-bar need high strength to resist permanent deformation (to avoid getting bent). One needs low elasticity the other needs high strength. The functional requirements are therefore not the same or even similar, so the analogy is in fact a bad one.

                          It is interesting to note that tungsten carbide boring bars (the ultimate boring bar) have a similar tensile strength as low carbon (mild) steel but also have an elastic modulus 3 or more times greater than that of any carbon or alloy steel. This in itself should tell you that resistance to elastic deflection is much more important than ultimate failure in any boring bar design.

                          If this were an old wives knitting circle (some might say that’s what it feels like at times) I would agree that a common understanding of the meaning of strength and rigidity might be a problem. However as this is a forum with a strong engineering lean I would propose that the most logical definition of these two words would be that assigned by the engineering community. Also it would be interesting to know what sample size you used to determine that it “is as most folks understand it”, just saying it doesn't make it so.

                          You can deny and propose alternatives all you like but it doesn’t change the engineering facts by one jot.

                          Originally posted by J Tiers
                          phooey.....

                          Perhaps YOU like your boring bars to permanently deform..... To each his own...... I prefer mine to spring back after deflecting, and you may suit yourself.

                          In case you do NOT want your boring bars to bend and permanently deflect, I suggest that the analogy is quite decent.... both tools are commonly long with respect to their diameter, both have a working end to which force is applied more-or-less perpendicular to the axis of the tool, and both must resist that force without deformation.

                          Perhaps you might like to reconsider your hasty statement............

                          Stronger? Well of course they are, but I deny that the "strength" is what is responded to.

                          People are not responding to the ultimate breaking strength, which is not being approached closely. They are responding to the fact that one can push much harder because the tool does not deform...... it has a *spring constant*, along with a larger elastic deflection, and that allows a larger force to be applied at the cost of a bit more temporary deflection.

                          Um.... I did say that I described what was as most folks understand it... pointing out thereby that it is not necessarily the technically correct description.....

                          but obviously deformation is an extreme form of deflection, insofar as the physical results in a structure or machine are concerned....

                          You quibble about the names, I see that the lifting arm is not lifting, but is laying on the ground, bent out of shape. Since that is presumably not the result I had in mind, I am considerably less interested in words, and more interested in the fact that it "deflected" plenty...... and not in a good way.

                          I offer you the alternate explanation that it "feels stronger and more rigid" because you can push harder with it. Something that bends out of the way and stays bent (elastic limit was exceeded) is not called "strong" as far as whatever usage it was put to....

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                          • #43
                            Evan, You made my morning. Boring bar...The exciting ones were where I almost got in a fight. Boring or exciting and not much else, might explain my machining hobby....

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                            • #44
                              If this were an old wives knitting circle ....
                              But it is. The only difference is which way we position the toilet seat.

                              See here about Knitting with wire.
                              Free software for calculating bolt circles and similar: Click Here

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                              • #45
                                @joelee: what inserts are theese?

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