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

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  • PixMan
    replied
    Originally posted by dian
    @joelee: what inserts are theese?
    I'm not JoeLee, but I can take a good guess. Without scale in the photo it's impossible to be certain about size, but the shapes are easy.

    They appear to be a 7؛ side clearnace angle. If so, the ones with the chipbreaker around the edge are usually referred to as TPMR, while the flat-topped one is TPGT.

    In ANSI desgination it would be as follows:

    TPMR21.51-PM2 (the "PM2" being PURE speculation as a chipbreaker designation is manufacturer-specific.)
    TPMR32.51-PM2
    TPGT21.51
    TPGT32.51 (no chipbreaker)

    In ISO designation the possibility would be:

    TPMT110204-PM2
    TPMT16T304-PM2
    TPMW110204
    TPMW16T304

    They may also use a G or H in the 3rd character position for tighter size tolerance inserts (ground periphery, usually). K is also used, but usually for milling inserts.

    If the inserts are the 5؛ side clearance angle, then:

    TCMT, TCGT, TCMW, TCMM, etc.

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  • lazlo
    replied
    Originally posted by precisionmetal
    I think it's probably fair to say that the majority of us have never broken a boring bar.
    More importantly, wouldn't you want the boring bar to yield (fracture) before the cast iron dovetail on your topslide?

    That's the nice thing about carbide boring bars -- very stiff, but very brittle. So if you have a crash, the boring bar gives, instead of the lathe.
    You can easily snap a thinner carbide boring bar from chatter, or even advancing the saddle into a blind hole. Ask me how I know

    I've been involved with go-kart racing for over 35 years, and all the modern sprint racing go karts have changeable axles for the conditions. The manufacturers all label them from "soft" to "hard". Despite all of them having the same ID and OD, the vast majority of racers believe that a "soft" flexes (deflects under a given load) more than a "hard" axle will under the same load.
    No offense to the racing community, but my experience has been that they're very superstitious. The racing community is the biggest market for cryogenic treatment, for example, and it's not for conversion of retained austenite immediately after heat treatment, as done for high alloy tooling.

    The hardness/stiffness fallacy is common in bladesmithing too -- many folks intuitively think that a hardened blade is less flexible than a differentially hardened (hard edge, soft spine) blade. But several eminent metallurgists will take out an old-school double-edged "safety razor", which is around 64 Rockwell, and bend it end to end. It snaps back to flat with no plastic deformation at all. A rapier or a filet knife is just as flexible, fully hardened or annealed. It's the geometry that makes the blade flexible, not the hardness.
    Last edited by lazlo; 11-05-2011, 12:25 PM.

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  • precisionmetal
    replied
    Originally posted by philbur
    If you want variation in flex why not just play with the ID or OD or both. How do the manufacturers designate the difference. Do they just call then soft, medium and hard etc?

    Phil
    That was essentially my point: the Italian chassis manufacturers (where literally 95% of the innovation comes from in kart racing) discovered a long time ago that it really isn't the "amount" of flex in the rear axle that fine tunes the feel of the chassis -- rather it's the "springiness" or "deadness" of the axle that is used to adjust the feel under various conditions.

    Boring bars can act similarly -- if you have one that is vibrating/ringing during cutting, you can change its tuned frequency (and/or damp it) by clamping a piece of metal to the bar. Clamp a piece of steel to it, or clamp a piece of lead to it... and the bar will respond differently.

    fwiw...

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  • philbur
    replied
    If you want variation in flex why not just play with the ID or OD or both. How do the manufacturers designate the difference. Do they just call then soft, medium and hard etc?

    Phil

    Originally posted by precisionmetal
    The manufacturers all label them from "soft" to "hard". Despite all of them having the same ID and OD, the vast majority of racers believe that a "soft" flexes (deflects under a given load) more than a "hard" axle will under the same load.

    Leave a comment:


  • beanbag
    replied
    Today in a CNC mishap, I managed to jam a tool into my insert toolholder made out of annealed 4140. It cracked the insert and put a gouge in the pocket. If it had been hardened, it probably wouldn't have gouged.

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  • precisionmetal
    replied
    I think it's probably fair to say that the majority of us have never broken a boring bar.

    It's probably also fair to say that not many of us have ever bent (permanently) a boring bar.

    That said: I'll add something else to the fray: a softer (as in Rc) boring bar will "act" different than a hard one -- and I'm speaking about using it well within its yield limit.

    I've been involved with go-kart racing for over 35 years, and all the modern sprint racing go karts have changeable axles for the conditions. The manufacturers all label them from "soft" to "hard". Despite all of them having the same ID and OD, the vast majority of racers believe that a "soft" flexes (deflects under a given load) more than a "hard" axle will under the same load. Technically that is of course impossible, however I can assure you that they most definitely "feel" different on the racetrack. Different axles for different conditions. I can hang one up holding it by one and and give it a smack with a wrench (so it rings), and can just about tell you how it will feel on the racetrack.

    A long story, but point being that boring bars (if they are not overly huge so there is no movement whatsoever) will "feel" different if they are fully heat treated or dead soft.

    my 2c.

    Leave a comment:


  • lazlo
    replied
    Originally posted by JoeLee
    I made these little boring bars out of a soft steel, not sure what it was, it machined beautifully like lead alloy steel does.
    Easy to tell if it's 12L14 -- have they rusted already?

    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.
    As has been said, all steels have the same stiffness, regardless of hardness. You're good to go

    A SAE Grade 8 Bolt is supposed to be made from alloy steel (per IFI)... which would mean typically 41XX range.
    That was my understanding as well. That although AISI/SAE doesn't specify the exactly alloy, they do indicate:

    Grade 8: "Medium Carbon Alloy Steel [AKA, Chromoly], Quenched and Tempered"
    Grade 5: "Medium Carbon Steel [AKA, 1045], Quenched and Tempered"
    Grade 1: "Low or Medium Carbon Steel"

    http://www.americanfastener.com/tech...ings_steel.asp
    Last edited by lazlo; 11-04-2011, 07:40 PM.

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  • Chris S.
    replied
    Originally posted by jep24601
    J Tiers is addressing "Rigidity" which is not necessarily the same as "Stiffness".
    Stiffness is very clearly defined as ExI (modulus x Moment of Inertia)
    Rigidity is a more general term often used to relate to assemblies rather than individual members or parts. One for instance would normally refer to how rigidly a boring bar is held rather than how stiffly it is held.

    Ah! Semantics.
    A good explanation for us old guys.

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  • jep24601
    replied
    J Tiers is addressing "Rigidity" which is not necessarily the same as "Stiffness".
    Stiffness is very clearly defined as ExI (modulus x Moment of Inertia)
    Rigidity is a more general term often used to relate to assemblies rather than individual members or parts. One for instance would normally refer to how rigidly a boring bar is held rather than how stiffly it is held.

    Ah! Semantics.

    Leave a comment:


  • J Tiers
    replied
    Originally posted by philbur
    You have exceed the yield strength, which, in the context of this particluar discussion, is effectively the same thing as untimate strength.

    Permanent deflection (correct term deformation) is a direct consequence of exceeding the yield strength.

    Phil

    PS: You appear to be switched to the engineering definitions of untimate strength and yield strength.

    "Breaking strength" is not exceeded, obviously.......

    The deformation point (yield point) is equally obviously exceeded... at least "locally", but clearly not throughout the thickness of the material.

    if the breaking strength (ultimate strength, etc) had been exceeded, the wire would have, well, BROKEN......

    Again, you are arguing correctness in a case where I have specifically stated I am NOT TALKING ABOUT technical definitions, but about the "observables" obvious to the non-technical person.

    If you pull test a sample, the yield point is reached and the curve has a "knee " in it. But after that, the material does not actually "break" until a somewhat higher "pull" is applied. It usually necks down, work-hardens, and eventually breaks at some point a few percent higher.

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  • philbur
    replied
    You have exceed the yield strength, which, in the context of this particluar discussion, is effectively the same thing as untimate strength.

    Permanent deflection (correct term deformation) is a direct consequence of exceeding the yield strength.

    Phil

    PS: You appear to be switched to the engineering definitions of untimate strength and yield strength.

    Originally posted by J Tiers
    (The ultimate strength is not involved here, but the stress necessary to cause a permanent deflection IS directly involved.)
    Last edited by philbur; 11-04-2011, 05:34 AM.

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  • J Tiers
    replied
    Originally posted by philbur
    You can deny and propose alternatives all you like but it doesn’t change the engineering facts by one jot.
    The problem here is that you-all are insisting that everyone think the correct way. Most folks are not engineers...... a fact which ensures that engineers get paid.

    I know ALL ABOUT the biz of the modulus..... don't be fooled into thinking that I am arguing about that.....

    What I am saying is that there ARE "properties" of hardened material which vary significantly from those of non-hardened, and that the properties folks are responding to are not what you think.

    Specifically, a piece of soft wire may simply fold up and is unable to be used as a "spring" to, for instance, push some heavy object on a table.

    But that same wire, if hardened properly, may be perfectly able to do that......

    It is obvious from that sort of demonstration that the "maximum force exertable" through the hardened wire is in excess of that exertable with the unhardened.....

    (The ultimate strength is not involved here, but the stress necessary to cause a permanent deflection IS directly involved.)

    For most folks, that "means" the hardened wire is more "rigid"..... they say, with some justification, "after all, one folded up and the other didn't..... what else would you call it?" And as far as they are concerned, your techie mumbo-jumbo is so much double-talk and hooey unless you can make it clear.

    If your intent is to educate, the first thing you must do is observe what the wrong beliefs are. It does no good to repeatedly spout the same technical words...... That is like one who believes a foreigner will understand the local language better if the local citizen repeats the same words but speaks more slowly and much louder.....

    You need to understand why your audience believes what they (wrongly) believe, before you can effectively correct them.

    My statements were aimed at showing the basis of "most folks" misunderstanding..... NOT, as you apparently presume, at denying engineering facts..... Engineering facts get me paid on a regular basis, so I rather like them.

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  • dian
    replied
    @joelee: what inserts are theese?

    Leave a comment:


  • Evan
    replied
    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.

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  • Abner
    replied
    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....

    Leave a comment:

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