What kind of boring bar is this?
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    Default What kind of boring bar is this?

    hi all, see picture, I need to cut a keyway as shown. I just don't know what that type of boring bar with a crossways tool holder that is called, or where to get one.

    If anyone could point me in the direction, that would be appreciated!



    boring-bar-keyway.jpg

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    Quote Originally Posted by FlyinChip View Post
    hi all, see picture, I need to cut a keyway as shown. I just don't know what that type of boring bar with a crossways tool holder that is called, or where to get one.

    If anyone could point me in the direction, that would be appreciated!



    boring-bar-keyway.jpg
    I made the one I have, easy peasy.

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    That is the home made kind.

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    Tool Bit Holder Sets | MSCDirect.com

    MSC #00228270 el cheapo "boring tool bit holder" set. You didn't say what diameter, but start with this @$68.00. Just get a matching square tool bit and grind it to do your keyway.

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    what material to make the boring bar with? I would think that anything soft enough to drill crosswise (if thats what you do), would not be rigid enough. I did find "double end boring bar" on ebay with 3/16" square tool holding (set screw holds the hss).

    i'm pretty new at this, as is pretty obvious. but already starting to understand this one. so thanks for the info

    I have a 1/2" diameter boring bar holder for my qc toolpost, so 1/2" bar.

    lathe is a SB Heavy 10

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    Cold-rolled (1018) works ok. 1/2" diameter is pretty thin if you are trying to cut a long keyway though. If it is a wide keyway you can use a narrower cutter and do it in two sections which will cut down on the cutting and bending forces. I've use such on a mill with a rapid feed handle but it seems to me it will be a tough go on a lathe without a long-throw carriage motion.

    I have cut 3/8" keyways on the mill, in two passes and it takes a lot of strokes and a fair amount of pressure. You'll need a sharp cutter with adequate relief on both sides. If your lathe has a high geared carriage like the smaller South Bends it will take a lot of force on the handwheel. I personally would probably not attempt to use power feed for that.

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    Quote Originally Posted by FlyinChip View Post
    what material to make the boring bar with? I would think that anything soft enough to drill crosswise (if thats what you do), would not be rigid enough.
    My terms may be totally wrong.. But. HARDNESS or SOFTNESS of a STEEL bar has nothing to do with
    how much force it takes to deflect it.. Modulus of Elasticy or something (8am Class, I slept
    through materials)..

    How far you have to bend it to permanently deflect it, or how much it wears, or how much torque
    it can take before you rip the threads out, that's a different story...

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    Get a broach and an arbor press. You will be done quicker and cheaper without scrapping a bunch of parts

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    and the rack on the lathe.

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    My preferred steel for bars is 8620.

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    To answer your question, I like just about any cold rolled steel for the bar although toughened alloy is probably best. I've cut keyways in a lathe but never really liked it. I have to concur with Spurewell on his suggestion.

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    1144 worked well for this one, its 2" dia.

    For 12" P&W vertical shaper
    Attached Thumbnails Attached Thumbnails p1000340sm.jpg  

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    hardness has nothing to do with rigidity. all steel has the same rigidity. it all deflects the same amount when loaded with the same force. up to the point it bends permanently. hardness determines how much force it takes to permanently bend (yield)

    irrelevant for you since your going to be taking very light cuts just scraping your way to depth.

    use the biggest, shortest bar practical. drill a hole through it, and put a bit in it. a broken endmill properly ground would be perfect. start scraping away. about .001" at a time Don't brute force it.

    reversing the bit and cutting on the retract stroke will go better on a flimsy setup because it will not tend to dig in.

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    thank you everyone for the great info. I ended up buying a 1/4" dumont broach set on ebay, hopefully it's in good condition. I also will practice with the boring bar method on some scrap pieces when I get around to it.

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    Quote Originally Posted by dsergison View Post
    hardness has nothing to do with rigidity. all steel has the same rigidity. it all deflects the same amount when loaded with the same force. up to the point it bends permanently. hardness determines how much force it takes to permanently bend (yield)
    I'm not sure I understand this statement. Rigidity by definition is the measure of resistance to the force required to "yield". Saying that 2" x 6" long piece of 4140 has the same Rigidity as a piece of 'same dimensions' 1018, is hard to believe.

    So if it isn't hardness that makes a thing more Rigid, than what is? Density maybe? IE, a solid Carbide Bar normally for me is a 6-1 overhang ratio, and Steel is 4-1 ratio, very different Hardness'. Not asking about set-up or any other variables, just simple chunks of Metal.

    I'm asking out of ignorance.

    R

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    Quote Originally Posted by litlerob1 View Post
    I'm not sure I understand this statement. Rigidity by definition is the measure of resistance to the force required to "yield". Saying that 2" x 6" long piece of 4140 has the same Rigidity as a piece of 'same dimensions' 1018, is hard to believe.

    So if it isn't hardness that makes a thing more Rigid, than what is? Density maybe? IE, a solid Carbide Bar normally for me is a 6-1 overhang ratio, and Steel is 4-1 ratio, very different Hardness'. Not asking about set-up or any other variables, just simple chunks of Metal.

    I'm asking out of ignorance.

    R
    This is very common confusion.

    Stiffness or rigidity for different steel grades or hardness is the same as long as the part or "bar" doesn't bend permanently. (AKA elastic deformation)
    With 200lbs load a 1" diameter and 2' long dead soft 1018 bends same amount as HRC 60 hardened carbon steel. But you are able to put more load on the hardened rod without making permanent bend.

    "Young's modulus" or elastic modulus is the property you are after if you want to make something very "stiff" (and its practically the same for all the steel grades and hardnesses)
    Young's modulus - Wikipedia

    List includes some other suprises also like that titanium is less "stiff" than copper: titanium 110GPa vs. copper 117GPa

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    Quote Originally Posted by litlerob1 View Post
    I'm not sure I understand this statement. Rigidity by definition is the measure of resistance to the force required to "yield". Saying that 2" x 6" long piece of 4140 has the same Rigidity as a piece of 'same dimensions' 1018, is hard to believe.

    So if it isn't hardness that makes a thing more Rigid, than what is? Density maybe? IE, a solid Carbide Bar normally for me is a 6-1 overhang ratio, and Steel is 4-1 ratio, very different Hardness'. Not asking about set-up or any other variables, just simple chunks of Metal.

    I'm asking out of ignorance.

    R


    Rigidity or stiffness as a basic material property is the "spring rate" or Young's Modulus of the given material. Put a sample in a tensile-tester, pull on it, measure the stress(sample force per crosssection area) divided by the deflection (in the elastic range, before it yields)= the modulus of elasticity(spring rate). The "yield point" and "tensile (breaking)" strength are usually generally referred to as "strength" (versus "stiffness") of a material. For basic steel types and common iron/steel alloys, the modulus, or spring rate is about the same(which is non-intuitive)(between 28 to 30 million psi); alloys and heat treating can modify the yield point, tensile, fatigue and other properties quite dramatically, but not the basic spring-rate.

    Carbide, for example (a totally different animal than steel alloys (technically a ceramic-metal composite) has a modulus of 70-90 million psi, so it's 2-3 times as stiff as steel of the same geometry.

    Generally, hardness does correlate with stiffness, and obviously more brittleness (brittle materials go from from elastic to rupture, no "plastic" deformation or yield region), density would not particularly correlate to stiffness/high modulus (gold, lead etc). For ceramics (aluminum oxide, zirconia etc), for example, the stiffness is so high, and they're so brittle (can't reliably clamp a specimen in a tensile tester and pull it), that a different property and test is used ("modulus of rupture" and flexural strength), where samples are bent in a 3 or 4-point fixture and the flexural strength is indirectly calculated from formulas. Cheers.

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    I think your confusion is in your understanding of yield. Yield is the point of permanent deformation.

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    Okay, thanks. Now lets talk about Machining, the biggest challenge with Boring as an operation, is vibration. Based on teh above information and Young's Modulus, in a Boring operation a Bar made of 1018 is going to deflect the same amount as a Hardened Bar of 4340. Obviously we aren't making Bars out of A36 or 1018 for that matter--why not? It would be cheaper.

    It seems to me, on a molecular level that all things "yield" to a degree, right? The Atomic construction changes if the Bar's molecules are altered (flexing IE) Interesting stuff here, to me at least.

    R

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    Quote Originally Posted by litlerob1 View Post
    Okay, thanks. Now lets talk about Machining, the biggest challenge with Boring as an operation, is vibration. Based on teh above information and Young's Modulus, in a Boring operation a Bar made of 1018 is going to deflect the same amount as a Hardened Bar of 4340. Obviously we aren't making Bars out of A36 or 1018 for that matter--why not? It would be cheaper.


    R
    I have made couple of ad-hoc boring bars out of cold drawn 1018 and they perform just the same as hardened 4340 withing limits.

    -toolpost screws leave dents on soft boring bar
    -if insert tooling the insert pockets won't hold size for long. Less of a problem if you use stick of HSS on the end of the boring bar but the hole can still bell-mouth in frequent use.

    Young's modulus is the "reason" to use solid carbide or heavy metal boring bars.


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